v3.26.1
Unaudited Consolidated Schedule of Investments (Additional Information)
€ in Millions, £ in Millions, kr in Millions, $ in Millions, $ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2026
USD ($)
Mar. 31, 2025
USD ($)
Dec. 31, 2025
USD ($)
Mar. 31, 2026
AUD ($)
Mar. 31, 2026
EUR (€)
Mar. 31, 2026
GBP (£)
Mar. 31, 2026
SEK (kr)
Dec. 31, 2025
EUR (€)
Dec. 31, 2025
GBP (£)
Dec. 31, 2025
SEK (kr)
Derivative [Line Items]                    
Value at Settlement $ 241.7   $ 209.6              
Current Value 242.2   220.0              
Derivatives Available for Offset 2.0   0.0              
Unrealized Appreciation (Depreciation) $ (0.7)   $ (10.4)              
Percent of net assets 232.60% [1]   222.40% [2] 232.60% [1] 232.60% [1] 232.60% [1] 232.60% [1] 222.40% [2] 222.40% [2] 222.40% [2]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3] $ 13,008.6                  
Net Realized Gain (Loss) (195.0) $ (18.0)                
Net Change in Unrealized Appreciation (Depreciation) (377.0) (14.0)                
Fair Value, ending balance 12,269.4 [1],[4]   $ 13,008.6 [2],[3]              
PIK Income $ 38.0 64.0                
Qualifying Assets                    
Derivative [Line Items]                    
Percent of net assets 74.20%   70.60% 74.20% 74.20% 74.20% 74.20% 70.60% 70.60% 70.60%
Euro Interbank Offered Rate                    
Derivative [Line Items]                    
Variable rate 2.08%     2.08% 2.08% 2.08% 2.08%      
BBSY                    
Derivative [Line Items]                    
Variable rate 4.36%   3.79% 4.36% 4.36% 4.36% 4.36% 3.79% 3.79% 3.79%
STIBOR                    
Derivative [Line Items]                    
Variable rate 2.19%   1.96% 2.19% 2.19% 2.19% 2.19% 1.96% 1.96% 1.96%
SONIA                    
Derivative [Line Items]                    
Variable rate 3.85%   3.72% 3.85% 3.85% 3.85% 3.85% 3.72% 3.72% 3.72%
Secured Overnight Financing Rate (SOFR)                    
Derivative [Line Items]                    
Variable rate 3.68%   3.65% 3.68% 3.68% 3.68% 3.68% 3.65% 3.65% 3.65%
Euro Interbank Offer Rate (EURIBOR)                    
Derivative [Line Items]                    
Variable rate     2.03%         2.03% 2.03% 2.03%
CDOR                    
Derivative [Line Items]                    
Variable rate     2.26%         2.26% 2.26% 2.26%
Non-controlled/affiliated                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance $ 854.6 1,140.0 $ 1,140.0              
Gross Additions 17.1 [5]   179.6 [6]              
Gross Reductions (109.5) [7]   (376.5) [8]              
Net Realized Gain (Loss) (98.0) 9.0 (2.3)              
Net Change in Unrealized Appreciation (Depreciation) 10.0 (20.0) (86.2)              
Fair Value, ending balance 674.2   854.6              
Investment Income 1.0 [9]   30.0 [10]              
PIK Income 11.9 [9] 18.0 66.0 [10]              
Fee income 0.0 [9] 3.0 3.6 [10]              
Dividend and Other Income 1.6 [9] 9.0 23.6 [10]              
Controlled/affiliated                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 3,990.5 3,776.7 3,776.7              
Gross Additions 254.5 [11]   1,395.5 [12]              
Gross Reductions (203.8) [13]   (1,002.2) [14]              
Net Realized Gain (Loss) (55.7) 13.0 (73.7)              
Net Change in Unrealized Appreciation (Depreciation) (147.8) (52.0) (105.8)              
Fair Value, ending balance 3,837.7   3,990.5              
Investment Income 8.2 [15]   43.0 [16]              
PIK Income 20.3 [15] 28.0 88.5 [16]              
Fee income 0.0 [15] 0.0 1.1 [16]              
Dividend and Other Income 67.3 [15] 60.0 283.4 [16]              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,AUD, March, 2028                    
Derivative [Line Items]                    
Value at Settlement 0.4     $ 0.7            
Current Value 0.4                  
Derivatives Available for Offset 0.0                  
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,EUR, December, 2029                    
Derivative [Line Items]                    
Value at Settlement 6.5   6.6   € 5.7     € 5.7    
Current Value 6.8   7.0              
Derivatives Available for Offset 0.3   (0.4)              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,EUR, February, 2028                    
Derivative [Line Items]                    
Value at Settlement 5.2       € 4.6          
Current Value 5.4                  
Derivatives Available for Offset 0.2                  
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,EUR, February, 2028                    
Derivative [Line Items]                    
Value at Settlement     5.2         € 4.6    
Current Value     5.5              
Derivatives Available for Offset     (0.3)              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,GBP, January, 2026                    
Derivative [Line Items]                    
Value at Settlement     7.5           £ 6.2  
Current Value     8.3              
Derivatives Available for Offset     (0.8)              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,GBP, April, 2026                    
Derivative [Line Items]                    
Value at Settlement     4.3           3.5  
Current Value     4.7              
Derivatives Available for Offset     (0.4)              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,GBP, April, 2026 1                    
Derivative [Line Items]                    
Value at Settlement 4.7         £ 3.5        
Current Value 4.6                  
Derivatives Available for Offset 0.1                  
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,GBP, April, 2026 2                    
Derivative [Line Items]                    
Value at Settlement 4.3         3.5        
Current Value 4.6                  
Derivatives Available for Offset 0.3                  
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,GBP, August, 2026 1                    
Derivative [Line Items]                    
Value at Settlement 6.0   6.0     4.8     4.8  
Current Value 6.3   6.4              
Derivatives Available for Offset 0.3   (0.4)              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,GBP, August, 2026 2                    
Derivative [Line Items]                    
Value at Settlement 10.8   10.8     8.6     8.6  
Current Value 11.4   11.6              
Derivatives Available for Offset 0.6   (0.8)              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,GBP, December, 2026 1                    
Derivative [Line Items]                    
Value at Settlement 1.3         1.0        
Current Value 1.3                  
Derivatives Available for Offset 0.0                  
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,GBP, December, 2026 2                    
Derivative [Line Items]                    
Value at Settlement 36.4         27.3        
Current Value 35.8                  
Derivatives Available for Offset 0.6                  
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,GBP, February, 2028                    
Derivative [Line Items]                    
Value at Settlement     11.1           8.6  
Current Value     11.5              
Derivatives Available for Offset     (0.4)              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,GBP, June, 2027                    
Derivative [Line Items]                    
Value at Settlement 8.3         6.2        
Current Value 8.1                  
Derivatives Available for Offset 0.2                  
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,GBP, March, 2026 1                    
Derivative [Line Items]                    
Value at Settlement     2.0           1.5  
Current Value     2.0              
Derivatives Available for Offset     0.0              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,GBP, March, 2026 2                    
Derivative [Line Items]                    
Value at Settlement     16.6           13.5  
Current Value     18.1              
Derivatives Available for Offset     (1.5)              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,GBP, March, 2029                    
Derivative [Line Items]                    
Value at Settlement     10.6           8.0  
Current Value     10.7              
Derivatives Available for Offset     (0.1)              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,GBP, September, 2026 1                    
Derivative [Line Items]                    
Value at Settlement 28.9   28.9     21.7     21.7  
Current Value 28.5   29.1              
Derivatives Available for Offset 0.4   (0.2)              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,GBP, September, 2026 2                    
Derivative [Line Items]                    
Value at Settlement 37.1   37.1     27.8     £ 27.8  
Current Value 36.6   37.3              
Derivatives Available for Offset 0.5   (0.2)              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,GBP, September, 2026 3                    
Derivative [Line Items]                    
Value at Settlement 18.0         13.5        
Current Value 17.8                  
Derivatives Available for Offset 0.2                  
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,SEK, April, 2027                    
Derivative [Line Items]                    
Value at Settlement     11.3             kr 115.1
Current Value     12.7              
Derivatives Available for Offset     (1.4)              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,SEK, December, 2029                    
Derivative [Line Items]                    
Value at Settlement 5.7   5.7       kr 57.3     57.3
Current Value 6.2   6.5              
Derivatives Available for Offset 0.5   (0.8)              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,SEK, February, 2028                    
Derivative [Line Items]                    
Value at Settlement 5.3   5.3       54.8     54.8
Current Value 5.9   6.1              
Derivatives Available for Offset 0.6   (0.8)              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,SEK, February, 2028                    
Derivative [Line Items]                    
Value at Settlement 11.1         8.6        
Current Value 11.2                  
Derivatives Available for Offset (0.1)                  
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,SEK, June, 2027                    
Derivative [Line Items]                    
Value at Settlement     6.7             69.8
Current Value     7.9              
Derivatives Available for Offset     (1.2)              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,SEK, June, 2027                    
Derivative [Line Items]                    
Value at Settlement 2.6           27.0      
Current Value 2.9                  
Derivatives Available for Offset 0.3                  
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,SEK, June, 2028 1                    
Derivative [Line Items]                    
Value at Settlement 27.6   27.6       251.7     251.7
Current Value 27.1   28.1              
Derivatives Available for Offset 0.5   (0.5)              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,SEK, June, 2028 2                    
Derivative [Line Items]                    
Value at Settlement 6.3   6.3       kr 58.5     kr 58.5
Current Value 6.3   6.5              
Derivatives Available for Offset 0.0   (0.2)              
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,SEK, March, 2028                    
Derivative [Line Items]                    
Value at Settlement 4.6         3.5        
Current Value 4.6                  
Derivatives Available for Offset 0.0                  
Open Forward Foreign Currency Contract, Identifier [Axis]: JP Morgan Chase Bank ,SEK, March, 2029                    
Derivative [Line Items]                    
Value at Settlement 10.6         £ 8.0        
Current Value 10.4                  
Derivatives Available for Offset 0.2                  
Investment, Identifier [Axis]: 3Pillar Global Inc | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 3.1                  
Fair Value, ending balance 2.6 [4],[18]   3.1 [2],[3],[17]              
Investment, Identifier [Axis]: 3Pillar Global Inc | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[19] 117.6                  
Fair Value, ending balance 109.9 [4],[18],[20]   117.6 [2],[3],[17],[19]              
Investment, Identifier [Axis]: 3Pillar Global Inc | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 5.7                  
Fair Value, ending balance 5.7 [4],[22]   5.7 [2],[3],[21]              
Investment, Identifier [Axis]: 48Forty Solutions LLC 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 86.0 [23] 148.5 148.5              
Gross Additions 0.0 [5],[23]   6.3 [6]              
Gross Reductions (85.7) [7],[23]   (0.4) [8]              
Net Realized Gain (Loss) (93.8) [23]   0.0              
Net Change in Unrealized Appreciation (Depreciation) 93.5 [23]   (68.4)              
Fair Value, ending balance [23] 0.0   86.0              
Investment Income 0.0 [9],[23]   1.7 [10]              
PIK Income 0.0 [9],[23]   6.3 [10]              
Fee income 0.0 [9],[23]   0.0 [10]              
Dividend and Other Income 0.0 [9],[23]   0.0 [10]              
Investment, Identifier [Axis]: 48Forty Solutions LLC 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 2.9 [23] 3.0 3.0              
Gross Additions 0.0 [5],[23]   4.4 [6]              
Gross Reductions (4.1) [7],[23]   (0.7) [8]              
Net Realized Gain (Loss) (4.2) [23]   0.0              
Net Change in Unrealized Appreciation (Depreciation) 5.4 [23]   (3.8)              
Fair Value, ending balance [23] 0.0   2.9              
Investment Income 0.0 [9],[23]   0.2 [10]              
PIK Income 0.0 [9],[23]   0.0 [10]              
Fee income 0.0 [9],[23]   0.0 [10]              
Dividend and Other Income 0.0 [9],[23]   0.0 [10]              
Investment, Identifier [Axis]: 48Forty Solutions LLC 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [24] 0.0                  
Gross Additions [11],[24] 15.8                  
Gross Reductions [13],[24] 0.0                  
Net Realized Gain (Loss) [24] 0.0                  
Net Change in Unrealized Appreciation (Depreciation) [24] 0.5                  
Fair Value, ending balance [24] 16.3   0.0              
Investment Income [15],[24] 0.3                  
PIK Income [15],[24] 0.0                  
Fee income [15],[24] 0.0                  
Dividend and Other Income [15],[24] 0.0                  
Investment, Identifier [Axis]: 48Forty Solutions LLC 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [24] 0.0                  
Gross Additions [11],[24] 20.2                  
Gross Reductions [13],[24] 0.0                  
Net Realized Gain (Loss) [24] 0.0                  
Net Change in Unrealized Appreciation (Depreciation) [24] 0.6                  
Fair Value, ending balance [24] 20.8   0.0              
Investment Income [15],[24] 0.4                  
PIK Income [15],[24] 0.0                  
Fee income [15],[24] 0.0                  
Dividend and Other Income [15],[24] 0.0                  
Investment, Identifier [Axis]: 48Forty Solutions LLC | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25],[26],[27] 86.0                  
Fair Value, ending balance 16.3 [4],[18],[28]   86.0 [2],[3],[17],[25],[26],[27]              
Investment, Identifier [Axis]: 48Forty Solutions LLC | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25],[26],[27] 4.0                  
Fair Value, ending balance 20.8 [4],[18],[28]   4.0 [2],[3],[17],[25],[26],[27]              
Investment, Identifier [Axis]: 48Forty Solutions LLC | Commercial & Professional Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[25],[26],[27] 1.0                  
Fair Value, ending balance 6.3 [4],[22],[28]   1.0 [2],[3],[21],[25],[26],[27]              
Investment, Identifier [Axis]: 48Forty Solutions LLC | Commercial & Professional Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [4],[22],[28] 1.6                  
Investment, Identifier [Axis]: 48Forty Solutions LLC, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions [6]     0.0              
Gross Reductions [8]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.0              
Fair Value, ending balance     0.0              
Investment Income [10]     0.0              
PIK Income [10]     0.0              
Fee income [10]     0.0              
Dividend and Other Income [10]     0.0              
Investment, Identifier [Axis]: 48Forty Solutions LLC, Common Stock 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [23] 0.0                  
Gross Additions [5],[23] 0.0                  
Gross Reductions [7],[23] 0.0                  
Net Realized Gain (Loss) [23] 0.0                  
Net Change in Unrealized Appreciation (Depreciation) [23] 0.0                  
Fair Value, ending balance [23] 0.0   0.0              
Investment Income [9],[23] 0.0                  
PIK Income [9],[23] 0.0                  
Fee income [9],[23] 0.0                  
Dividend and Other Income [9],[23] 0.0                  
Investment, Identifier [Axis]: 48Forty Solutions LLC, Common Stock 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [24] 0.0                  
Gross Additions [11],[24] 0.5                  
Gross Reductions [13],[24] 0.0                  
Net Realized Gain (Loss) [24] 0.0                  
Net Change in Unrealized Appreciation (Depreciation) [24] (0.5)                  
Fair Value, ending balance [24] 0.0   0.0              
Investment Income [15],[24] 0.0                  
PIK Income [15],[24] 0.0                  
Fee income [15],[24] 0.0                  
Dividend and Other Income [15],[24] 0.0                  
Investment, Identifier [Axis]: 48Forty Solutions LLC, Common Stock | Commercial & Professional Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25],[26] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[28],[29]   0.0 [2],[3],[17],[25],[26]              
Investment, Identifier [Axis]: 48Forty Solutions LLC, Preferred Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0                  
Gross Additions [11] 55.6                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) (10.1)                  
Fair Value, ending balance 45.5   0.0              
Investment Income [15] 0.0                  
PIK Income [15] 0.0                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: 48Forty Solutions LLC, Preferred Stock | Commercial & Professional Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[29] 45.5                  
Investment, Identifier [Axis]: 801 5th Ave, Seattle, ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   (0.1) [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.1              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: 801 5th Ave, Seattle, ABF Equity , Equity Real Estate Investment Trusts (REITs)                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30],[31] 0.0                  
Fair Value, ending balance [2],[3],[17],[26],[30],[31]     0.0              
Investment, Identifier [Axis]: 801 5th Ave, Seattle, ABF Equity | Equity Real Estate Investment Trusts (REITs)                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[29] 0.0                  
Investment, Identifier [Axis]: 801 5th Ave, Seattle, Structure Mezzanine                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 49.8 54.5 54.5              
Gross Additions 0.1 [11]   2.1 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (3.5)   (6.8)              
Fair Value, ending balance 46.4   49.8              
Investment Income 1.5 [15]   6.2 [16]              
PIK Income 0.0 [15]   1.9 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: 801 5th Ave, Seattle, Structured Mezzanine , Equity Real Estate Investment Trusts (REITs)                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 49.8                  
Fair Value, ending balance [2],[3],[17],[30],[31]     49.8              
Investment, Identifier [Axis]: 801 5th Ave, Seattle, Structured Mezzanine | Equity Real Estate Investment Trusts (REITs)                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[29],[32] 46.4                  
Investment, Identifier [Axis]: A-Lign Assurance LLC | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33] 10.9                  
Fair Value, ending balance 10.6 [4],[18],[34]   10.9 [2],[3],[17],[33]              
Investment, Identifier [Axis]: A-Lign Assurance LLC | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.2                  
Fair Value, ending balance 3.1 [4],[22]   3.2 [2],[3],[21]              
Investment, Identifier [Axis]: A-Lign Assurance LLC | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 1.5                  
Fair Value, ending balance 1.5 [4],[22]   1.5 [2],[3],[21]              
Investment, Identifier [Axis]: AGS Health LLC | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33] 17.3                  
Fair Value, ending balance 5.8 [4],[18],[34]   17.3 [2],[3],[17],[33]              
Investment, Identifier [Axis]: AGS Health LLC | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 6.0                  
Fair Value, ending balance 11.0 [4],[18],[34]   6.0 [2],[3],[21]              
Investment, Identifier [Axis]: AGS Health LLC | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 2.1                  
Fair Value, ending balance 5.8 [4],[22]   2.1 [2],[3],[21]              
Investment, Identifier [Axis]: AGS Health LLC | Software & Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [4],[22] 2.1                  
Investment, Identifier [Axis]: AOP SFR 1 LLC (FKA Avenue One PropCo), ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 6.3                  
Gross Additions [11] 0.2                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) (1.4)                  
Fair Value, ending balance 5.1   6.3              
Investment Income [15] 0.0                  
PIK Income [15] 0.0                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: AOP SFR 1 LLC (FKA Avenue One PropCo), ABF Equity | Equity Real Estate Investment Trusts (REITs)                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [4],[18],[28],[29] 5.1                  
Investment, Identifier [Axis]: AOP SFR 1 LLC (FKA Avenue One PropCo), Term Loan                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 34.7                  
Gross Additions [11] 0.6                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 0.0                  
Fair Value, ending balance 35.3   34.7              
Investment Income [15] 0.0                  
PIK Income [15] 0.6                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: AOP SFR 1 LLC (FKA Avenue One PropCo), Term Loan | Equity Real Estate Investment Trusts (REITs)                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [4],[18],[28] 35.3                  
Investment, Identifier [Axis]: ATX Networks Corp                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 3.9 32.9 32.9              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (3.9)   (29.0)              
Fair Value, ending balance 0.0   3.9              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: ATX Networks Corp , Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[27],[30],[31],[35] 3.9                  
Fair Value, ending balance [2],[3],[17],[26],[27],[30],[31],[35]     3.9              
Investment, Identifier [Axis]: ATX Networks Corp 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 37.0 37.0              
Gross Additions [12]     1.1              
Gross Reductions [14]     (37.5)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     (0.6)              
Fair Value, ending balance     0.0              
Investment Income [16]     0.0              
PIK Income [16]     1.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: ATX Networks Corp 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 27.9 15.3 15.3              
Gross Additions 1.0 [11]   12.6 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 28.9   27.9              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 1.1 [15]   2.3 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: ATX Networks Corp 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 93.0 50.6 50.6              
Gross Additions 1.0 [11]   43.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (21.5)   (0.6)              
Fair Value, ending balance 72.5   93.0              
Investment Income 0.0 [15]   0.2 [16]              
PIK Income 0.0 [15]   9.1 [16]              
Fee income 0.0 [15]   1.1 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: ATX Networks Corp | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[29],[32],[36] 0.0                  
Investment, Identifier [Axis]: ATX Networks Corp | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 27.9                  
Fair Value, ending balance 28.9 [4],[18],[28],[36]   27.9 [2],[3],[17],[30],[31]              
Investment, Identifier [Axis]: ATX Networks Corp | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31],[35] 93.0                  
Fair Value, ending balance 72.5 [4],[18],[28],[29],[32],[36]   93.0 [2],[3],[17],[30],[31],[35]              
Investment, Identifier [Axis]: ATX Networks Corp, Class B-1 Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) (5.0)   0.0              
Net Change in Unrealized Appreciation (Depreciation) 5.0   0.0              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: ATX Networks Corp, Class B-1 Common Stock | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30],[31] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[28],[29],[36]   0.0 [2],[3],[17],[26],[30],[31]              
Investment, Identifier [Axis]: ATX Networks Corp, Class B-2 Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) (4.0)   0.0              
Net Change in Unrealized Appreciation (Depreciation) 4.0   0.0              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: ATX Networks Corp, Class B-2 Common Stock | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30],[31] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[28],[29],[36]   0.0 [2],[3],[17],[26],[30],[31]              
Investment, Identifier [Axis]: ATX Networks Corp, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) (9.9)   0.0              
Net Change in Unrealized Appreciation (Depreciation) 9.9   0.0              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: ATX Networks Corp, Common Stock | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30],[31],[35] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[28],[29],[36]   0.0 [2],[3],[17],[26],[30],[31],[35]              
Investment, Identifier [Axis]: AVE Holdings I Corp (fka Amerivet Partners Management Inc), Preferred Stock | Health Care Equipment & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[29],[32] 2.0                  
Investment, Identifier [Axis]: AVE Holdings I Corp | Health Care Equipment & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [4],[18],[37] 61.2                  
Investment, Identifier [Axis]: AVE Holdings I Corp | Health Care Equipment & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [4],[22] 7.7                  
Investment, Identifier [Axis]: Aareon AG | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 4.2                  
Fair Value, ending balance 4.0 [4],[18],[36]   4.2 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Aareon AG | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 11.4                  
Fair Value, ending balance 11.1 [4],[22],[36]   11.4 [2],[3],[21],[31]              
Investment, Identifier [Axis]: Abacus JV, ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.8 24.6 24.6              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   (27.0) [14]              
Net Realized Gain (Loss) 0.0   0.7              
Net Change in Unrealized Appreciation (Depreciation) 0.0   2.5              
Fair Value, ending balance 0.8   0.8              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Abacus JV, ABF Equity , Insurance                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30],[31] 0.8                  
Fair Value, ending balance [2],[3],[17],[26],[30],[31]     0.8              
Investment, Identifier [Axis]: Abacus JV, ABF Equity | Insurance                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[29],[36] 0.8                  
Investment, Identifier [Axis]: Accelerator Investments Aggregator LP, ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.6                  
Gross Additions [5] 0.0                  
Gross Reductions [7] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 0.0                  
Fair Value, ending balance 0.6   0.6              
Investment Income [9] 0.0                  
PIK Income [9] 0.0                  
Fee income [9] 0.0                  
Dividend and Other Income [9] 0.0                  
Investment, Identifier [Axis]: Accelerator Investments Aggregator LP, ABF Equity , Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25],[26],[31] 0.6                  
Fair Value, ending balance [2],[3],[17],[25],[26],[31]     0.6              
Investment, Identifier [Axis]: Accelerator Investments Aggregator LP, ABF Equity | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[29],[36],[38] 0.6                  
Investment, Identifier [Axis]: Accelerator Investments Aggregator LP, Private Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.6 0.9 0.9              
Gross Additions [6]     0.0              
Gross Reductions [8]     (0.4)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.1              
Fair Value, ending balance     0.6              
Investment Income [10]     0.0              
PIK Income [10]     0.0              
Fee income [10]     0.0              
Dividend and Other Income [10]     0.0              
Investment, Identifier [Axis]: Accuride Corp                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 6.4 0.0 0.0              
Gross Additions 0.1 [11]   4.3 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (0.5)   2.1              
Fair Value, ending balance 6.0   6.4              
Investment Income 0.0 [15]   0.1 [16]              
PIK Income 0.1 [15]   0.1 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Accuride Corp , Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30] 6.4                  
Fair Value, ending balance [2],[3],[17],[30]     6.4              
Investment, Identifier [Axis]: Accuride Corp | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28] 6.0                  
Investment, Identifier [Axis]: Accuride Corp, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Accuride Corp, Common Stock | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[28],[29]   0.0 [2],[3],[17],[26],[30]              
Investment, Identifier [Axis]: Accuride Corp, Preferred Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Accuride Corp, Preferred Stock | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[28],[29]   0.0 [2],[3],[17],[26],[30]              
Investment, Identifier [Axis]: Actium Holdings Ltd (fka Alpha Financial Markets Consulting) | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [4],[18],[36] 3.5                  
Investment, Identifier [Axis]: Actium Holdings Ltd (fka Alpha Financial Markets Consulting) | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [4],[22],[36] 2.3                  
Investment, Identifier [Axis]: Advanced Dermatology & Cosmetic Surgery | Health Care Equipment & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 0.5                  
Fair Value, ending balance 1.4 [4],[18]   0.5 [2],[3],[17]              
Investment, Identifier [Axis]: Advanced Dermatology & Cosmetic Surgery | Health Care Equipment & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39],[40] 44.9                  
Fair Value, ending balance 44.8 [4],[18],[34],[37],[41]   44.9 [2],[3],[17],[33],[39],[40]              
Investment, Identifier [Axis]: Advanced Dermatology & Cosmetic Surgery | Health Care Equipment & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.1                  
Fair Value, ending balance 2.1 [4],[22]   3.1 [2],[3],[21]              
Investment, Identifier [Axis]: Advania Sverige AB | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31],[42] 5.9                  
Fair Value, ending balance 5.2 [4],[18],[36],[43]   5.9 [2],[3],[17],[31],[42]              
Investment, Identifier [Axis]: Advania Sverige AB | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 69.1                  
Fair Value, ending balance 66.4 [4],[18],[36]   69.1 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Advania Sverige AB | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 17.5                  
Fair Value, ending balance 16.6 [4],[18],[36]   17.5 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Affordable Care Inc 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 11.8                  
Gross Additions [5] 0.0                  
Gross Reductions [7] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) (2.6)                  
Fair Value, ending balance 9.2   11.8              
Investment Income [9] 0.0                  
PIK Income [9] 0.0                  
Fee income [9] 0.0                  
Dividend and Other Income [9] 0.0                  
Investment, Identifier [Axis]: Affordable Care Inc 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 54.2                  
Gross Additions [5] 0.0                  
Gross Reductions [7] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) (11.9)                  
Fair Value, ending balance 42.3   54.2              
Investment Income [9] 0.0                  
PIK Income [9] 0.0                  
Fee income [9] 0.0                  
Dividend and Other Income [9] 0.0                  
Investment, Identifier [Axis]: Affordable Care Inc 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 44.6 35.2 35.2              
Gross Additions [6]     13.6              
Gross Reductions [8]     (1.0)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     (3.2)              
Fair Value, ending balance     44.6              
Investment Income [10]     3.1              
PIK Income [10]     1.1              
Fee income [10]     0.0              
Dividend and Other Income [10]     0.0              
Investment, Identifier [Axis]: Affordable Care Inc 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 21.4 22.2 22.2              
Gross Additions [6]     0.7              
Gross Reductions [8]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     (1.5)              
Fair Value, ending balance     21.4              
Investment Income [10]     1.7              
PIK Income [10]     0.7              
Fee income [10]     0.0              
Dividend and Other Income [10]     0.0              
Investment, Identifier [Axis]: Affordable Care Inc | Health Care Equipment & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25] 11.8                  
Fair Value, ending balance 9.2 [4],[18],[29],[32],[38]   11.8 [2],[3],[17],[25]              
Investment, Identifier [Axis]: Affordable Care Inc | Health Care Equipment & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25],[39] 54.2                  
Fair Value, ending balance 42.3 [4],[18],[29],[32],[38]   54.2 [2],[3],[17],[25],[39]              
Investment, Identifier [Axis]: Affordable Care Inc | Health Care Equipment & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[25] 0.1                  
Fair Value, ending balance 0.1 [4],[22],[29],[32],[38]   0.1 [2],[3],[21],[25]              
Investment, Identifier [Axis]: Affordable Care Inc, Preferred Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 72.3 73.1 73.1              
Gross Additions 0.0 [5]   9.9 [6]              
Gross Reductions 0.0 [7]   0.0 [8]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (70.6)   (10.7)              
Fair Value, ending balance 1.7   72.3              
Investment Income 0.0 [9]   0.0 [10]              
PIK Income 0.0 [9]   9.9 [10]              
Fee income 0.0 [9]   0.0 [10]              
Dividend and Other Income 0.0 [9]   0.0 [10]              
Investment, Identifier [Axis]: Affordable Care Inc, Preferred Stock | Health Care Equipment & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25] 72.3                  
Fair Value, ending balance 1.7 [1],[4],[18],[29],[32],[38]   72.3 [2],[3],[17],[25]              
Investment, Identifier [Axis]: Alacrity Solutions Group LLC                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 3.8 0.0 0.0              
Gross Additions 0.1 [11]   3.8 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (0.6)   0.0              
Fair Value, ending balance 3.3   3.8              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.1 [15]   0.4 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Alacrity Solutions Group LLC , Insurance                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30] 3.8                  
Fair Value, ending balance [2],[3],[17],[30]     3.8              
Investment, Identifier [Axis]: Alacrity Solutions Group LLC 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 10.7 0.0 0.0              
Gross Additions 0.1 [11]   10.6 [12]              
Gross Reductions (7.1) [13]   0.0 [14]              
Net Realized Gain (Loss) 0.1   0.0              
Net Change in Unrealized Appreciation (Depreciation) (0.1)   0.1              
Fair Value, ending balance 3.7   10.7              
Investment Income 0.0 [15]   0.6 [16]              
PIK Income 0.1 [15]   0.3 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Alacrity Solutions Group LLC 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.1 0.0 0.0              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions (0.1) [13]   0.0 [14]              
Net Realized Gain (Loss) 0.1   0.0              
Net Change in Unrealized Appreciation (Depreciation) (0.1)   0.1              
Fair Value, ending balance 0.0   0.1              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Alacrity Solutions Group LLC | Insurance                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28] 3.3                  
Investment, Identifier [Axis]: Alacrity Solutions Group LLC | Insurance 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30] 0.1                  
Fair Value, ending balance 3.7 [4],[18],[28]   0.1 [2],[3],[17],[30]              
Investment, Identifier [Axis]: Alacrity Solutions Group LLC | Insurance 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30] 10.7                  
Fair Value, ending balance 1.7 [4],[22],[28]   10.7 [2],[3],[17],[30]              
Investment, Identifier [Axis]: Alacrity Solutions Group LLC | Insurance 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[30] 1.7                  
Fair Value, ending balance 2.3 [4],[22],[28]   1.7 [2],[3],[21],[30]              
Investment, Identifier [Axis]: Alacrity Solutions Group LLC | Insurance 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[30] 2.3                  
Fair Value, ending balance [2],[3],[21],[30]     2.3              
Investment, Identifier [Axis]: Alacrity Solutions Group LLC, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions 0.0 [11]   1.9 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   (1.9)              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Alacrity Solutions Group LLC, Common Stock | Insurance                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[28],[29]   0.0 [2],[3],[17],[26],[30]              
Investment, Identifier [Axis]: Alacrity Solutions Group LLC, Preferred Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.7 0.0 0.0              
Gross Additions 0.0 [11]   2.3 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (0.6)   (1.6)              
Fair Value, ending balance 0.1   0.7              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.2 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Alacrity Solutions Group LLC, Preferred Equity | Insurance                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[27],[30] 0.7                  
Fair Value, ending balance 0.1 [1],[4],[18],[28],[29],[32]   0.7 [2],[3],[17],[26],[27],[30]              
Investment, Identifier [Axis]: Alpha Financial Markets Consulting PLC | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 3.5                  
Fair Value, ending balance [2],[3],[17],[31]     3.5              
Investment, Identifier [Axis]: Alpha Financial Markets Consulting PLC | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 2.3                  
Fair Value, ending balance [2],[3],[21],[31]     2.3              
Investment, Identifier [Axis]: Altavair AirFinance, ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 48.6 128.2 128.2              
Gross Additions 0.0 [5]   0.0 [6]              
Gross Reductions (11.6) [7]   (82.4) [8]              
Net Realized Gain (Loss) 0.0   (1.0)              
Net Change in Unrealized Appreciation (Depreciation) 0.4   3.8              
Fair Value, ending balance 37.4   48.6              
Investment Income 0.0 [9]   0.0 [10]              
PIK Income 0.0 [9]   0.0 [10]              
Fee income 0.0 [9]   0.0 [10]              
Dividend and Other Income 1.2 [9]   20.0 [10]              
Investment, Identifier [Axis]: Altavair AirFinance, ABF Equity , Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25],[31] 48.6                  
Fair Value, ending balance [2],[3],[17],[25],[31]     48.6              
Investment, Identifier [Axis]: Altavair AirFinance, ABF Equity | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[36],[38] 37.4                  
Investment, Identifier [Axis]: American Vision Partners | Health Care Equipment & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 3.1                  
Fair Value, ending balance 89.3 [4],[18],[20],[34],[37]   3.1 [2],[3],[17]              
Investment, Identifier [Axis]: American Vision Partners | Health Care Equipment & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[19],[33],[39] 89.5                  
Fair Value, ending balance 7.8 [4],[22]   89.5 [2],[3],[17],[19],[33],[39]              
Investment, Identifier [Axis]: American Vision Partners | Health Care Equipment & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 4.7                  
Fair Value, ending balance [2],[3],[21]     4.7              
Investment, Identifier [Axis]: American Vision Partners, Private Equity | Health Care Equipment & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26] 2.2                  
Fair Value, ending balance 2.3 [1],[4],[18],[29]   2.2 [2],[3],[17],[26]              
Investment, Identifier [Axis]: Amerivet Partners Management Inc | Health Care Equipment & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[39] 65.6                  
Fair Value, ending balance [2],[3],[17],[39]     65.6              
Investment, Identifier [Axis]: Amerivet Partners Management Inc | Health Care Equipment & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 8.2                  
Fair Value, ending balance [2],[3],[21]     8.2              
Investment, Identifier [Axis]: Amerivet Partners Management Inc, Preferred Stock | Health Care Equipment & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[27] 12.6                  
Fair Value, ending balance [2],[3],[17],[26],[27]     12.6              
Investment, Identifier [Axis]: Apex Group Limited | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31],[42] 2.3                  
Fair Value, ending balance 2.2 [4],[18],[36],[43]   2.3 [2],[3],[17],[31],[42]              
Investment, Identifier [Axis]: Apex Service Partners LLC | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 1.3                  
Fair Value, ending balance 2.4 [4],[18]   1.3 [2],[3],[17]              
Investment, Identifier [Axis]: Apex Service Partners LLC | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33] 31.3                  
Fair Value, ending balance 31.2 [4],[18],[34]   31.3 [2],[3],[17],[33]              
Investment, Identifier [Axis]: Apex Service Partners LLC | Commercial & Professional Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 93.7                  
Fair Value, ending balance 93.4 [4],[18],[34],[37]   93.7 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Apex Service Partners LLC | Commercial & Professional Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.8                  
Fair Value, ending balance 2.8 [4],[22]   3.8 [2],[3],[21]              
Investment, Identifier [Axis]: Arcfield Acquisition Corp | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 6.0                  
Fair Value, ending balance 6.0 [4],[22]   6.0 [2],[3],[21]              
Investment, Identifier [Axis]: Arcwood Environmental (fka Heritage Environmental Services Inc) | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 52.5                  
Fair Value, ending balance 52.4 [4],[18],[34],[37]   52.5 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Arcwood Environmental (fka Heritage Environmental Services Inc) | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 16.7                  
Fair Value, ending balance 16.6 [4],[18],[34],[37]   16.7 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Arcwood Environmental (fka Heritage Environmental Services Inc) | Commercial & Professional Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 8.0                  
Fair Value, ending balance 8.0 [4],[22]   8.0 [2],[3],[21]              
Investment, Identifier [Axis]: Area Wide Protective Inc | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33] 14.3                  
Fair Value, ending balance 14.3 [4],[18],[34]   14.3 [2],[3],[17],[33]              
Investment, Identifier [Axis]: Area Wide Protective Inc | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 12.1                  
Fair Value, ending balance 12.1 [4],[22]   12.1 [2],[3],[21]              
Investment, Identifier [Axis]: Australis Maritime II, ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 23.3 19.8 19.8              
Gross Additions 0.0 [11]   9.8 [12]              
Gross Reductions 0.0 [13]   (7.0) [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.3   0.7              
Fair Value, ending balance 23.6   23.3              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   1.4 [16]              
Investment, Identifier [Axis]: Australis Maritime II, ABF Equity , Transportation                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 23.3                  
Fair Value, ending balance [2],[3],[17],[30],[31]     23.3              
Investment, Identifier [Axis]: Australis Maritime II, ABF Equity | Transportation                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[36] 23.6                  
Investment, Identifier [Axis]: Australis Maritime, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 1.2 11.3 11.3              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   (10.3) [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.2   0.2              
Fair Value, ending balance 1.4   1.2              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.2 [16]              
Investment, Identifier [Axis]: Australis Maritime, Common Stock , Transportation                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 1.2                  
Fair Value, ending balance [2],[3],[17],[30],[31]     1.2              
Investment, Identifier [Axis]: Australis Maritime, Common Stock | Transportation                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[36] 1.4                  
Investment, Identifier [Axis]: Auxilior Capital Partners Inc, Preferred Equity , Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 20.1                  
Fair Value, ending balance [2],[3],[17]     20.1              
Investment, Identifier [Axis]: Auxilior Capital Partners Inc, Preferred Equity | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18] 20.4                  
Investment, Identifier [Axis]: Avenue One PropCo, ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 6.3 10.2 10.2              
Gross Additions [12]     0.0              
Gross Reductions [14]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     (3.9)              
Fair Value, ending balance     6.3              
Investment Income [16]     0.0              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Avenue One PropCo, ABF Equity , Equity Real Estate Investment Trusts (REITs)                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30],[31] 6.3                  
Fair Value, ending balance [2],[3],[17],[26],[30],[31]     6.3              
Investment, Identifier [Axis]: Avenue One PropCo, Term Loan                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 34.7 32.3 32.3              
Gross Additions [12]     2.4              
Gross Reductions [14]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.0              
Fair Value, ending balance     34.7              
Investment Income [16]     0.0              
PIK Income [16]     2.4              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Avenue One PropCo, Term Loan , Equity Real Estate Investment Trusts (REITs)                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 34.7                  
Fair Value, ending balance [2],[3],[17],[30],[31]     34.7              
Investment, Identifier [Axis]: Avetta LLC | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[39] 8.4                  
Fair Value, ending balance 8.4 [4],[18],[37]   8.4 [2],[3],[39]              
Investment, Identifier [Axis]: Avetta LLC | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 1.8                  
Fair Value, ending balance 1.8 [4],[22]   1.8 [2],[3],[21]              
Investment, Identifier [Axis]: Avetta LLC | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 0.8                  
Fair Value, ending balance 0.8 [4],[22]   0.8 [2],[3],[21]              
Investment, Identifier [Axis]: Avetta LLC | Software & Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.7                  
Fair Value, ending balance 3.7 [4],[22]   3.7 [2],[3],[21]              
Investment, Identifier [Axis]: Avida Holding AB, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 51.7 60.4 60.4              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (4.2)   (8.7)              
Fair Value, ending balance 47.5   51.7              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Avida Holding AB, Common Stock , Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30],[31] 51.7                  
Fair Value, ending balance [2],[3],[17],[26],[30],[31]     51.7              
Investment, Identifier [Axis]: Avida Holding AB, Common Stock | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[29],[36] 47.5                  
Investment, Identifier [Axis]: Avida Holding AB, Subordinated Bond                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 1.6 1.3 1.3              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.3              
Fair Value, ending balance 1.6   1.6              
Investment Income 0.0 [15]   0.2 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Avida Holding AB, Subordinated Bond , Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 1.6                  
Fair Value, ending balance [2],[3],[17],[30],[31]     1.6              
Investment, Identifier [Axis]: Avida Holding AB, Subordinated Bond | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[36] 1.6                  
Investment, Identifier [Axis]: BCA Marketplace Ltd | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 66.8                  
Fair Value, ending balance 7.8 [4],[18],[36]   66.8 [2],[3],[17],[31]              
Investment, Identifier [Axis]: BCA Marketplace Ltd | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 5.4                  
Fair Value, ending balance 5.3 [4],[18],[36]   5.4 [2],[3],[17],[31]              
Investment, Identifier [Axis]: BDO USA PA | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 27.8                  
Fair Value, ending balance 27.6 [4],[18],[34],[37]   27.8 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: BDO USA PA | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 1.4                  
Fair Value, ending balance 1.4 [4],[18]   1.4 [2],[3],[17]              
Investment, Identifier [Axis]: BGB Group LLC | Media & Entertainment 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 26.0                  
Fair Value, ending balance 25.9 [4],[18],[37]   26.0 [2],[3],[17]              
Investment, Identifier [Axis]: BGB Group LLC | Media & Entertainment 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.2                  
Fair Value, ending balance 3.2 [4],[22]   3.2 [2],[3],[21]              
Investment, Identifier [Axis]: BGB Group LLC | Media & Entertainment 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 4.8                  
Fair Value, ending balance 4.8 [4],[22]   4.8 [2],[3],[21]              
Investment, Identifier [Axis]: Belk Inc                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 23.1 29.5 29.5              
Gross Additions 0.0 [5]   0.0 [6]              
Gross Reductions (2.7) [7]   (6.6) [8]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.2              
Fair Value, ending balance 20.4   23.1              
Investment Income 0.8 [9]   3.8 [10]              
PIK Income 0.0 [9]   0.0 [10]              
Fee income 0.0 [9]   0.0 [10]              
Dividend and Other Income 0.0 [9]   0.0 [10]              
Investment, Identifier [Axis]: Belk Inc | Consumer Discretionary Distribution & Retail                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25] 23.1                  
Fair Value, ending balance 20.4 [4],[18],[38]   23.1 [2],[3],[17],[25]              
Investment, Identifier [Axis]: Belk Inc, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 37.1 27.1 27.1              
Gross Additions 0.0 [5]   4.2 [6]              
Gross Reductions 0.0 [7]   0.0 [8]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (3.5)   5.8              
Fair Value, ending balance 33.6   37.1              
Investment Income 0.0 [9]   0.0 [10]              
PIK Income 0.0 [9]   0.0 [10]              
Fee income 0.0 [9]   0.0 [10]              
Dividend and Other Income 0.0 [9]   0.0 [10]              
Investment, Identifier [Axis]: Belk Inc, Common Stock | Consumer Discretionary Distribution & Retail                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25],[26] 37.1                  
Fair Value, ending balance 33.6 [1],[4],[18],[29],[38]   37.1 [2],[3],[17],[25],[26]              
Investment, Identifier [Axis]: Bond Aviation Holdings LLC, ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.1                  
Gross Additions [5] 0.0                  
Gross Reductions [7] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 0.0                  
Fair Value, ending balance 0.1   0.1              
Investment Income [9] 0.0                  
PIK Income [9] 0.0                  
Fee income [9] 0.0                  
Dividend and Other Income [9] 0.0                  
Investment, Identifier [Axis]: Bond Aviation Holdings LLC, ABF Equity , Transportation                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25],[26] 0.1                  
Fair Value, ending balance [2],[3],[17],[25],[26]     0.1              
Investment, Identifier [Axis]: Bond Aviation Holdings LLC, ABF Equity 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 4.9 0.0 0.0              
Gross Additions [6]     4.9              
Gross Reductions [8]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.0              
Fair Value, ending balance     4.9              
Investment Income [10]     0.1              
PIK Income [10]     0.0              
Fee income [10]     0.2              
Dividend and Other Income [10]     0.0              
Investment, Identifier [Axis]: Bond Aviation Holdings LLC, ABF Equity | Transportation                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[29],[38] 0.1                  
Investment, Identifier [Axis]: Bond Aviation Holdings LLC, Term Loan , Transportation 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25] 4.9                  
Fair Value, ending balance [2],[3],[17],[25]     4.9              
Investment, Identifier [Axis]: Bond Aviation Holdings LLC, Term Loan , Transportation 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25] 0.7                  
Fair Value, ending balance [2],[3],[17],[25]     0.7              
Investment, Identifier [Axis]: Bond Aviation Holdings LLC, Term Loan , Transportation 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[25] 13.6                  
Fair Value, ending balance [2],[3],[21],[25]     13.6              
Investment, Identifier [Axis]: Bond Aviation Holdings LLC, Term Loan , Transportation 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[25] 5.3                  
Fair Value, ending balance [2],[3],[21],[25]     5.3              
Investment, Identifier [Axis]: Bond Aviation Holdings LLC, Term Loan 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.7                  
Gross Additions [5] 0.0                  
Gross Reductions [7] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 0.0                  
Fair Value, ending balance 0.7   0.7              
Investment Income [9] 0.0                  
PIK Income [9] 0.0                  
Fee income [9] 0.0                  
Dividend and Other Income [9] 0.0                  
Investment, Identifier [Axis]: Bond Aviation Holdings LLC, Term Loan 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 4.9                  
Gross Additions [5] 6.6                  
Gross Reductions [7] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 0.0                  
Fair Value, ending balance 11.5   4.9              
Investment Income [9] 0.2                  
PIK Income [9] 0.0                  
Fee income [9] 0.0                  
Dividend and Other Income [9] 0.0                  
Investment, Identifier [Axis]: Bond Aviation Holdings LLC, Term Loan 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.1 0.0 0.0              
Gross Additions [6]     0.1              
Gross Reductions [8]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.0              
Fair Value, ending balance     0.1              
Investment Income [10]     0.0              
PIK Income [10]     0.0              
Fee income [10]     0.0              
Dividend and Other Income [10]     0.0              
Investment, Identifier [Axis]: Bond Aviation Holdings LLC, Term Loan 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.7 0.0 0.0              
Gross Additions [6]     0.7              
Gross Reductions [8]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.0              
Fair Value, ending balance     0.7              
Investment Income [10]     0.0              
PIK Income [10]     0.0              
Fee income [10]     0.0              
Dividend and Other Income [10]     0.0              
Investment, Identifier [Axis]: Bond Aviation Holdings LLC, Term Loan | Transportation 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[38] 11.5                  
Investment, Identifier [Axis]: Bond Aviation Holdings LLC, Term Loan | Transportation 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[38] 0.7                  
Investment, Identifier [Axis]: Bond Aviation Holdings LLC, Term Loan | Transportation 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22],[38] 11.3                  
Investment, Identifier [Axis]: Bond Aviation Holdings LLC, Term Loan | Transportation 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22],[38] 5.3                  
Investment, Identifier [Axis]: Bonterra LLC | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39],[40],[44] 134.3                  
Fair Value, ending balance 131.8 [4],[18],[34],[37],[41],[45]   134.3 [2],[3],[17],[33],[39],[40],[44]              
Investment, Identifier [Axis]: Bonterra LLC | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 2.5                  
Fair Value, ending balance 4.5 [4],[18]   2.5 [2],[3],[17]              
Investment, Identifier [Axis]: Bonterra LLC | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 14.4                  
Fair Value, ending balance 12.2 [4],[22]   14.4 [2],[3],[21]              
Investment, Identifier [Axis]: Borden (New Dairy Opco), Common Stock 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 11.1                  
Gross Additions [11] 0.0                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) (0.6)                  
Fair Value, ending balance 10.5   11.1              
Investment Income [15] 0.0                  
PIK Income [15] 0.0                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: Borden (New Dairy Opco), Common Stock 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 11.1 18.4 18.4              
Gross Additions [12]     0.0              
Gross Reductions [14]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     (7.3)              
Fair Value, ending balance     11.1              
Investment Income [16]     0.0              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Borden (New Dairy Opco), Common Stock | Food, Beverage & Tobacco                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[26],[30],[46],[47] 11.1                  
Fair Value, ending balance 10.5 [1],[4],[28],[29],[48],[49]   11.1 [2],[3],[26],[30],[46],[47]              
Investment, Identifier [Axis]: Bowery Farming Inc, Warrant | Food, Beverage & Tobacco                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[29]   0.0 [2],[3],[17],[26]              
Investment, Identifier [Axis]: Bowery Farming Inc, Warrants | Food, Beverage & Tobacco 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[29]   0.0 [2],[3],[17],[26]              
Investment, Identifier [Axis]: Bowery Farming Inc, Warrants | Food, Beverage & Tobacco 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[29]   0.0 [2],[3],[17],[26]              
Investment, Identifier [Axis]: Builders Capital Loan Acquisition Trust 2022-RTL1, Structured Mezzanine , Real Estate Management & Development                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 1.1                  
Fair Value, ending balance [2],[3],[17],[31]     1.1              
Investment, Identifier [Axis]: Builders Capital Loan Acquisition Trust 2022-RTL1, Structured Mezzanine | Real Estate Management & Development                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[29],[32],[36] 0.0                  
Investment, Identifier [Axis]: Byrider Finance LLC, ABF Equity , Automobiles & Components                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[50] 0.0                  
Fair Value, ending balance [2],[3],[17],[26],[50]     0.0              
Investment, Identifier [Axis]: Byrider Finance LLC, ABF Equity | Automobiles & Components                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[29],[51] 0.0                  
Investment, Identifier [Axis]: CDS US Intermediate Holdings Inc, Common Stock | Media & Entertainment                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[31] 19.2                  
Fair Value, ending balance 19.2 [1],[4],[18],[29],[36]   19.2 [2],[3],[17],[26],[31]              
Investment, Identifier [Axis]: CLEAResult Consulting Inc | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 18.2                  
Fair Value, ending balance 18.1 [1],[4],[18],[34],[37]   18.2 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: CLEAResult Consulting Inc | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 4.6                  
Fair Value, ending balance 4.6 [1],[4],[22]   4.6 [2],[3],[21]              
Investment, Identifier [Axis]: CLEAResult Consulting Inc | Commercial & Professional Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.0                  
Fair Value, ending balance 3.0 [1],[4],[22]   3.0 [2],[3],[21]              
Investment, Identifier [Axis]: CSafe Global | Transportation 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[40],[44] 86.8                  
Fair Value, ending balance 86.6 [1],[4],[18],[41],[45]   86.8 [2],[3],[17],[40],[44]              
Investment, Identifier [Axis]: CSafe Global | Transportation 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 20.5                  
Fair Value, ending balance 20.1 [1],[4],[18]   20.5 [2],[3],[17]              
Investment, Identifier [Axis]: CSafe Global | Transportation 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 2.3                  
Fair Value, ending balance 3.8 [1],[4],[18]   2.3 [2],[3],[17]              
Investment, Identifier [Axis]: CSafe Global | Transportation 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 9.2                  
Fair Value, ending balance 7.7 [1],[4],[22]   9.2 [2],[3],[21]              
Investment, Identifier [Axis]: Cadence Education LLC | Consumer Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 10.3                  
Fair Value, ending balance 14.1 [4],[18],[34]   10.3 [2],[3],[17]              
Investment, Identifier [Axis]: Cadence Education LLC | Consumer Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 8.5                  
Fair Value, ending balance 8.4 [4],[22]   8.5 [2],[3],[21]              
Investment, Identifier [Axis]: Cadence Education LLC | Consumer Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 4.0                  
Fair Value, ending balance [2],[3],[21]     4.0              
Investment, Identifier [Axis]: Cambrex Corp | Pharmaceuticals, Biotechnology & Life Sciences 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[39] 31.1                  
Fair Value, ending balance 31.0 [4],[18],[37]   31.1 [2],[3],[17],[39]              
Investment, Identifier [Axis]: Cambrex Corp | Pharmaceuticals, Biotechnology & Life Sciences 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 0.5                  
Fair Value, ending balance 1.9 [4],[18]   0.5 [2],[3],[17]              
Investment, Identifier [Axis]: Cambrex Corp | Pharmaceuticals, Biotechnology & Life Sciences 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 7.8                  
Fair Value, ending balance 9.5 [4],[18]   7.8 [2],[3],[21]              
Investment, Identifier [Axis]: Cambrex Corp | Pharmaceuticals, Biotechnology & Life Sciences 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 9.5                  
Fair Value, ending balance 6.4 [4],[22]   9.5 [2],[3],[21]              
Investment, Identifier [Axis]: Cambrex Corp | Pharmaceuticals, Biotechnology & Life Sciences 5                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 5.7                  
Fair Value, ending balance [2],[3],[21]     5.7              
Investment, Identifier [Axis]: Capital Automotive LP, ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 23.0 32.9 32.9              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions (0.2) [13]   (17.8) [14]              
Net Realized Gain (Loss) 0.0   6.7              
Net Change in Unrealized Appreciation (Depreciation) 0.9   1.2              
Fair Value, ending balance 23.7   23.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.3 [15]   1.7 [16]              
Investment, Identifier [Axis]: Capital Automotive LP, ABF Equity , Equity Real Estate Investment Trusts (REITs)                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 23.0                  
Fair Value, ending balance [2],[3],[17],[30],[31]     23.0              
Investment, Identifier [Axis]: Capital Automotive LP, ABF Equity | Equity Real Estate Investment Trusts (REITs)                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[36] 23.7                  
Investment, Identifier [Axis]: Capital Automotive LP, Structured Mezzanine                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 18.7 40.1 40.1              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions (0.3) [13]   (21.4) [14]              
Net Realized Gain (Loss) 0.0   0.1              
Net Change in Unrealized Appreciation (Depreciation) (0.1)   (0.1)              
Fair Value, ending balance 18.3   18.7              
Investment Income 0.5 [15]   2.8 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Capital Automotive LP, Structured Mezzanine , Equity Real Estate Investment Trusts (REITs)                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 18.7                  
Fair Value, ending balance [2],[3],[17],[30],[31]     18.7              
Investment, Identifier [Axis]: Capital Automotive LP, Structured Mezzanine | Equity Real Estate Investment Trusts (REITs)                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[36] 18.3                  
Investment, Identifier [Axis]: Carrier Fire Protection | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 0.8                  
Fair Value, ending balance 1.2 [4],[18]   0.8 [2],[3],[17]              
Investment, Identifier [Axis]: Carrier Fire Protection | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 10.2                  
Fair Value, ending balance 9.7 [1],[4],[18],[34],[37]   10.2 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Carrier Fire Protection | Commercial & Professional Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 2.8                  
Fair Value, ending balance 0.5 [1],[4],[18]   2.8 [2],[3],[17]              
Investment, Identifier [Axis]: Carrier Fire Protection | Commercial & Professional Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 1.8                  
Fair Value, ending balance 2.8 [1],[4],[18]   1.8 [2],[3],[21]              
Investment, Identifier [Axis]: Carrier Fire Protection | Commercial & Professional Services 5                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 2.1                  
Fair Value, ending balance 1.4 [1],[4],[22]   2.1 [2],[3],[21]              
Investment, Identifier [Axis]: Carrier Fire Protection | Commercial & Professional Services 6                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22] 2.1                  
Investment, Identifier [Axis]: Cengage Learning, Inc, Common Stock | Media & Entertainment                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26] 4.7                  
Fair Value, ending balance 4.7 [1],[4],[18],[29]   4.7 [2],[3],[17],[26]              
Investment, Identifier [Axis]: Circana Group (f.k.a. NPD Group) | Consumer Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 17.5                  
Fair Value, ending balance 17.5 [1],[4],[18],[34],[37]   17.5 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Circana Group (f.k.a. NPD Group) | Consumer Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 4.3                  
Fair Value, ending balance 4.3 [1],[4],[22]   4.3 [2],[3],[21]              
Investment, Identifier [Axis]: Civica Group Ltd | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 4.6                  
Fair Value, ending balance 4.4 [1],[4],[18],[36]   4.6 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Civica Group Ltd | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 5.1                  
Fair Value, ending balance 4.9 [1],[4],[22],[36]   5.1 [2],[3],[21],[31]              
Investment, Identifier [Axis]: Civica Group Ltd | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 4.5                  
Fair Value, ending balance 4.3 [1],[4],[22],[36]   4.5 [2],[3],[21],[31]              
Investment, Identifier [Axis]: Clarience Technologies LLC | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39],[40],[44] 86.8                  
Fair Value, ending balance 79.9 [1],[4],[18],[34],[37],[41],[45]   86.8 [2],[3],[17],[33],[39],[40],[44]              
Investment, Identifier [Axis]: Clarience Technologies LLC | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 2.6                  
Fair Value, ending balance 2.3 [1],[4],[18]   2.6 [2],[3],[17]              
Investment, Identifier [Axis]: Clarience Technologies LLC | Capital Goods 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 12.4                  
Fair Value, ending balance 11.0 [1],[4],[22]   12.4 [2],[3],[21]              
Investment, Identifier [Axis]: Clarience Technologies LLC | Capital Goods 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 27.6                  
Fair Value, ending balance 24.3 [1],[4],[22]   27.6 [2],[3],[21]              
Investment, Identifier [Axis]: Clarience Technologies LLC | Capital Goods 5                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 1.9                  
Fair Value, ending balance [2],[3],[21]     1.9              
Investment, Identifier [Axis]: Cloud Software Group Inc (fka TIBCO Software Inc) | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[42] 0.7                  
Fair Value, ending balance [2],[3],[17],[42]     0.7              
Investment, Identifier [Axis]: Cloud Software Group Inc | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[43] 0.7                  
Investment, Identifier [Axis]: ClubCorp Club Operations Inc | Consumer Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33] 18.1                  
Fair Value, ending balance 17.9 [1],[4],[18],[34]   18.1 [2],[3],[17],[33]              
Investment, Identifier [Axis]: ClubCorp Club Operations Inc | Consumer Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 5.7                  
Fair Value, ending balance 5.7 [1],[4],[22]   5.7 [2],[3],[21]              
Investment, Identifier [Axis]: ClubCorp Club Operations Inc | Consumer Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.4                  
Fair Value, ending balance 3.4 [1],[4],[22]   3.4 [2],[3],[21]              
Investment, Identifier [Axis]: Com Laude Group Ltd | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31],[52] 15.9                  
Fair Value, ending balance 15.6 [1],[4],[18],[36]   15.9 [2],[3],[17],[31],[52]              
Investment, Identifier [Axis]: Com Laude Group Ltd | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31],[52] 3.1                  
Fair Value, ending balance 3.1 [1],[4],[22],[36]   3.1 [2],[3],[21],[31],[52]              
Investment, Identifier [Axis]: Com Laude Group Ltd | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31],[52] 1.3                  
Fair Value, ending balance 1.2 [1],[4],[22],[36]   1.3 [2],[3],[21],[31],[52]              
Investment, Identifier [Axis]: Com Laude Group Ltd | Software & Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 3.0                  
Fair Value, ending balance 2.9 [1],[4],[22],[36]   3.0 [2],[3],[21],[31]              
Investment, Identifier [Axis]: Community Brands Inc | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 0.3                  
Fair Value, ending balance 48.6 [1],[4],[18],[34],[41]   0.3 [2],[3],[17]              
Investment, Identifier [Axis]: Community Brands Inc | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[40] 44.1                  
Fair Value, ending balance 3.6 [1],[4],[22]   44.1 [2],[3],[17],[33],[40]              
Investment, Identifier [Axis]: Community Brands Inc | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 4.1                  
Fair Value, ending balance [2],[3],[21]     4.1              
Investment, Identifier [Axis]: Community Brands Inc | Software & Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 7.1                  
Fair Value, ending balance [2],[3],[21]     7.1              
Investment, Identifier [Axis]: Conservice LLC | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18] 12.4                  
Investment, Identifier [Axis]: Conservice LLC | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22] 1.7                  
Investment, Identifier [Axis]: Consilium Safety Group AB | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 10.6                  
Fair Value, ending balance 10.6 [1],[4],[22],[36]   10.6 [2],[3],[21],[31]              
Investment, Identifier [Axis]: Constellis Holdings LLC                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [53] 0.0 7.0 7.0              
Gross Additions [6],[53]     0.0              
Gross Reductions [8],[53]     (6.8)              
Net Realized Gain (Loss) [53]     0.0              
Net Change in Unrealized Appreciation (Depreciation) [53]     (0.2)              
Fair Value, ending balance [53]     0.0              
Investment Income [10],[53]     0.0              
PIK Income [10],[53]     0.0              
Fee income [10],[53]     0.0              
Dividend and Other Income [10],[53]     0.0              
Investment, Identifier [Axis]: Constellis Holdings LLC | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 6.8                  
Fair Value, ending balance 2.3 [1],[4],[18],[29],[32]   6.8 [2],[3],[17]              
Investment, Identifier [Axis]: Constellis Holdings LLC, Preferred Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 3.4 3.4              
Gross Additions [6]     0.0              
Gross Reductions [8]     (3.2)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     (0.2)              
Fair Value, ending balance     0.0              
Investment Income [10]     0.0              
PIK Income [10]     0.0              
Fee income [10]     0.0              
Dividend and Other Income [10]     0.0              
Investment, Identifier [Axis]: Constellis Holdings LLC, Preferred Equity | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26] 0.8                  
Fair Value, ending balance 0.0 [1],[4],[18],[29]   0.8 [2],[3],[17],[26]              
Investment, Identifier [Axis]: Constellis Holdings LLC, Private Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions [6]     0.0              
Gross Reductions [8]     0.0              
Net Realized Gain (Loss)     (10.3)              
Net Change in Unrealized Appreciation (Depreciation)     10.3              
Fair Value, ending balance     0.0              
Investment Income [10]     0.0              
PIK Income [10]     0.0              
Fee income [10]     0.0              
Dividend and Other Income [10]     0.0              
Investment, Identifier [Axis]: Corsearch Intermediate Inc | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[39] 29.5                  
Fair Value, ending balance 26.6 [1],[4],[18],[37]   29.5 [2],[3],[17],[39]              
Investment, Identifier [Axis]: Credit Opportunities Partners JV, LLC                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 1,967.9 1,363.3 1,363.3              
Gross Additions 0.0 [11]   630.2 [12]              
Gross Reductions (189.0) [13]   0.0 [14]              
Net Realized Gain (Loss) (28.8)   0.0              
Net Change in Unrealized Appreciation (Depreciation) (43.4)   (25.6)              
Fair Value, ending balance 1,706.7   1,967.9              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 62.7 [15]   232.5 [16]              
Investment, Identifier [Axis]: Credit Opportunities Partners JV, LLC | Credit Opportunities Partners JV, LLC                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 1,967.9                  
Fair Value, ending balance 1,706.7 [1],[4],[18],[28],[36]   1,967.9 [2],[3],[17],[30],[31]              
Investment, Identifier [Axis]: Cubic Corp | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[27] 23.2                  
Fair Value, ending balance 0.0 [1],[4],[18],[29],[32]   23.2 [2],[3],[17],[26],[27]              
Investment, Identifier [Axis]: Cubic Corp, Common Stock | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[29]   0.0 [2],[3],[17],[26]              
Investment, Identifier [Axis]: Cubic Corp, Preferred Equity | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[27] 19.1                  
Fair Value, ending balance 0.0 [1],[4],[18],[29],[32]   19.1 [2],[3],[17],[26],[27]              
Investment, Identifier [Axis]: Cubic Corp, Preferred Stock | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26] 2.1                  
Fair Value, ending balance 0.0 [1],[4],[18],[29]   2.1 [2],[3],[17],[26]              
Investment, Identifier [Axis]: Cubic Corp, Warrant | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[29]   0.0 [2],[3],[17],[26]              
Investment, Identifier [Axis]: Curia Receivables II SPV LLC (FKA Curia Global Inc), Revolver , Pharmaceuticals, Biotechnology & Life Sciences 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 21.2                  
Fair Value, ending balance [2],[3],[17],[31]     21.2              
Investment, Identifier [Axis]: Curia Receivables II SPV LLC (FKA Curia Global Inc), Revolver , Pharmaceuticals, Biotechnology & Life Sciences 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 20.9                  
Fair Value, ending balance [2],[3],[21],[31]     20.9              
Investment, Identifier [Axis]: Curia Receivables II SPV LLC (FKA Curia Global Inc), Revolver | Pharmaceuticals, Biotechnology & Life Sciences 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[36] 21.2                  
Investment, Identifier [Axis]: Curia Receivables II SPV LLC (FKA Curia Global Inc), Revolver | Pharmaceuticals, Biotechnology & Life Sciences 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22],[36] 20.9                  
Investment, Identifier [Axis]: Cyncly Refinancing , Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 0.0                  
Fair Value, ending balance [2],[3],[17],[31]     0.0              
Investment, Identifier [Axis]: Cyncly Refinancing , Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 1.6                  
Fair Value, ending balance [2],[3],[21],[31]     1.6              
Investment, Identifier [Axis]: Cyncly Refinancing | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 3.1                  
Fair Value, ending balance 0.8 [1],[4],[18],[36]   3.1 [2],[3],[21],[31]              
Investment, Identifier [Axis]: Cyncly Refinancing | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 4.7                  
Fair Value, ending balance 3.0 [1],[4],[22],[36]   4.7 [2],[3],[21],[31]              
Investment, Identifier [Axis]: Cyncly Refinancing | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22],[36] 3.8                  
Investment, Identifier [Axis]: Cyncly Refinancing | Software & Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[36] 0.0                  
Investment, Identifier [Axis]: Cyncly Refinancing | Software & Services 5                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22],[36] 1.5                  
Investment, Identifier [Axis]: DOXA Insurance Holdings LLC | Insurance 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 0.4                  
Fair Value, ending balance 0.9 [1],[4],[18]   0.4 [2],[3],[17]              
Investment, Identifier [Axis]: DOXA Insurance Holdings LLC | Insurance 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 33.2                  
Fair Value, ending balance 43.2 [1],[4],[18],[34],[37]   33.2 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: DOXA Insurance Holdings LLC | Insurance 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 2.9                  
Fair Value, ending balance 2.3 [1],[4],[22]   2.9 [2],[3],[21]              
Investment, Identifier [Axis]: DOXA Insurance Holdings LLC | Insurance 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 18.8                  
Fair Value, ending balance 8.5 [1],[4],[22]   18.8 [2],[3],[21]              
Investment, Identifier [Axis]: Dedalus Finance GmbH | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31],[42] 1.2                  
Fair Value, ending balance 1.1 [1],[4],[18],[36],[43]   1.2 [2],[3],[17],[31],[42]              
Investment, Identifier [Axis]: Dental Care Alliance Inc | Health Care Equipment & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[27],[39] 63.7                  
Fair Value, ending balance 63.4 [1],[4],[18],[29],[32]   63.7 [2],[3],[17],[26],[27],[39]              
Investment, Identifier [Axis]: Dental Care Alliance Inc | Health Care Equipment & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[27],[39] 29.7                  
Fair Value, ending balance 29.6 [1],[4],[18],[29],[32]   29.7 [2],[3],[17],[26],[27],[39]              
Investment, Identifier [Axis]: Dental365 LLC | Health Care Equipment & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 0.5                  
Fair Value, ending balance 26.1 [1],[4],[18],[34],[37]   0.5 [2],[3],[17]              
Investment, Identifier [Axis]: Dental365 LLC | Health Care Equipment & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 24.4                  
Fair Value, ending balance 13.6 [1],[4],[18],[34]   24.4 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Dental365 LLC | Health Care Equipment & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33] 13.6                  
Fair Value, ending balance 5.1 [1],[4],[22]   13.6 [2],[3],[17],[33]              
Investment, Identifier [Axis]: Dental365 LLC | Health Care Equipment & Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 4.6                  
Fair Value, ending balance 1.9 [1],[4],[22]   4.6 [2],[3],[21]              
Investment, Identifier [Axis]: Dental365 LLC | Health Care Equipment & Services 5                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.6                  
Fair Value, ending balance [2],[3],[21]     3.6              
Investment, Identifier [Axis]: Discover Financial Services, ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 21.7 21.7              
Gross Additions [12]     0.0              
Gross Reductions [14]     (21.4)              
Net Realized Gain (Loss)     0.5              
Net Change in Unrealized Appreciation (Depreciation)     (0.8)              
Fair Value, ending balance     0.0              
Investment Income [16]     0.0              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     1.3              
Investment, Identifier [Axis]: Discover Financial Services, Subordinated Loan                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 38.8 38.8              
Gross Additions [12]     0.0              
Gross Reductions [14]     (38.8)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.0              
Fair Value, ending balance     0.0              
Investment Income [16]     2.7              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Diversified Energy Co PLC, Common Stock | Energy                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[31],[42],[47],[54] 21.4                  
Fair Value, ending balance [2],[3],[31],[42],[47],[54]     21.4              
Investment, Identifier [Axis]: Drive Revel, ABF Equity | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 22.2                  
Fair Value, ending balance 23.3 [1],[4],[18],[36]   22.2 [2],[3],[17],[31]              
Investment, Identifier [Axis]: DuBois Chemicals Inc | Materials 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39],[40] 50.1                  
Fair Value, ending balance 49.8 [1],[4],[18],[34],[37],[41]   50.1 [2],[3],[17],[33],[39],[40]              
Investment, Identifier [Axis]: DuBois Chemicals Inc | Materials 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 14.7                  
Fair Value, ending balance 14.7 [1],[4],[22]   14.7 [2],[3],[21]              
Investment, Identifier [Axis]: DuBois Chemicals Inc | Materials 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 4.3                  
Fair Value, ending balance 4.3 [1],[4],[22]   4.3 [2],[3],[21]              
Investment, Identifier [Axis]: Eagle Railcar Services Roscoe Inc | Transportation 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[39] 8.4                  
Fair Value, ending balance 8.3 [1],[4],[37]   8.4 [2],[3],[39]              
Investment, Identifier [Axis]: Eagle Railcar Services Roscoe Inc | Transportation 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 10.8                  
Fair Value, ending balance 10.8 [1],[4],[22]   10.8 [2],[3],[21]              
Investment, Identifier [Axis]: Eagle Railcar Services Roscoe Inc | Transportation 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 12.1                  
Fair Value, ending balance 12.0 [1],[4],[22]   12.1 [2],[3],[21]              
Investment, Identifier [Axis]: Envirotainer Ltd | Transportation                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 2.8                  
Fair Value, ending balance 2.8 [1],[4],[22],[36]   2.8 [2],[3],[21],[31]              
Investment, Identifier [Axis]: Excelitas Technologies Corp | Technology Hardware & Equipment 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[39] 1.9                  
Fair Value, ending balance 1.9 [1],[4],[37]   1.9 [2],[3],[39]              
Investment, Identifier [Axis]: Excelitas Technologies Corp | Technology Hardware & Equipment 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 2.4                  
Fair Value, ending balance 2.3 [1],[4],[22]   2.4 [2],[3],[21]              
Investment, Identifier [Axis]: Excelitas Technologies Corp | Technology Hardware & Equipment 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 22.6                  
Fair Value, ending balance 22.3 [1],[4],[22]   22.6 [2],[3],[21]              
Investment, Identifier [Axis]: Flexera Software LLC | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[44] 59.7                  
Fair Value, ending balance 59.3 [1],[4],[18],[34],[37],[45]   59.7 [2],[3],[17],[33],[44]              
Investment, Identifier [Axis]: Flexera Software LLC | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 1.7                  
Fair Value, ending balance 6.2 [1],[4],[22]   1.7 [2],[3],[17]              
Investment, Identifier [Axis]: Flexera Software LLC | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 6.5                  
Fair Value, ending balance [2],[3],[21]     6.5              
Investment, Identifier [Axis]: Follett Software Co | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[40] 19.0                  
Fair Value, ending balance 18.6 [1],[4],[18],[34],[41]   19.0 [2],[3],[17],[33],[40]              
Investment, Identifier [Axis]: Follett Software Co | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 5.6                  
Fair Value, ending balance 5.5 [1],[4],[22]   5.6 [2],[3],[21]              
Investment, Identifier [Axis]: Fortna AR LLC (FKA Fortna Group Inc), Revolver | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 36.9                  
Fair Value, ending balance [2],[3],[17],[31]     36.9              
Investment, Identifier [Axis]: Fortna AR LLC (FKA Fortna Group Inc), Revolver | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[36] 35.0                  
Investment, Identifier [Axis]: Fortna AR LLC (FKA Fortna Group Inc), Revolver | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22],[36] 2.0                  
Investment, Identifier [Axis]: Fortnox AB | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 8.8                  
Fair Value, ending balance 8.5 [1],[4],[22],[36]   8.8 [2],[3],[21],[31]              
Investment, Identifier [Axis]: Foundation Consumer Brands LLC | Pharmaceuticals, Biotechnology & Life Sciences 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 73.9                  
Fair Value, ending balance 70.0 [1],[4],[18],[34],[37]   73.9 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Foundation Consumer Brands LLC | Pharmaceuticals, Biotechnology & Life Sciences 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 7.7                  
Fair Value, ending balance 7.7 [1],[4],[22]   7.7 [2],[3],[21]              
Investment, Identifier [Axis]: Foundation Risk Partners Corp | Insurance 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 3.0                  
Fair Value, ending balance 2.2 [1],[4],[18]   3.0 [2],[3],[17]              
Investment, Identifier [Axis]: Foundation Risk Partners Corp | Insurance 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 93.5                  
Fair Value, ending balance 95.1 [1],[4],[18],[34],[37]   93.5 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Foundation Risk Partners Corp | Insurance 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 8.9                  
Fair Value, ending balance 9.6 [1],[4],[22]   8.9 [2],[3],[21]              
Investment, Identifier [Axis]: Foundation Risk Partners Corp | Insurance 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 6.6                  
Fair Value, ending balance 4.8 [1],[4],[22]   6.6 [2],[3],[21]              
Investment, Identifier [Axis]: Frontline Road Safety LLC | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[39] 46.9                  
Fair Value, ending balance 105.9 [1],[4],[18],[34],[37]   46.9 [2],[3],[17],[39]              
Investment, Identifier [Axis]: Frontline Road Safety LLC | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 59.0                  
Fair Value, ending balance 15.7 [1],[4],[22]   59.0 [2],[3],[17]              
Investment, Identifier [Axis]: Frontline Road Safety LLC | Capital Goods 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 15.7                  
Fair Value, ending balance 14.2 [1],[4],[22]   15.7 [2],[3],[21]              
Investment, Identifier [Axis]: Frontline Road Safety LLC | Capital Goods 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 14.3                  
Fair Value, ending balance [2],[3],[21]     14.3              
Investment, Identifier [Axis]: Fullsteam Holdings LLC | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33] 32.9                  
Fair Value, ending balance 31.8 [1],[4],[18],[34]   32.9 [2],[3],[17],[33]              
Investment, Identifier [Axis]: Fullsteam Holdings LLC | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 11.0                  
Fair Value, ending balance 10.6 [1],[4],[22]   11.0 [2],[3],[21]              
Investment, Identifier [Axis]: Fullsteam Holdings LLC | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.7                  
Fair Value, ending balance 3.5 [1],[4],[22]   3.7 [2],[3],[21]              
Investment, Identifier [Axis]: GE Digital LLC | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[41] 25.1                  
Investment, Identifier [Axis]: GE Digital LLC | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22] 4.5                  
Investment, Identifier [Axis]: Galaxy Container, ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.2 0.0 0.0              
Gross Additions 0.0 [11]   0.2 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 0.2   0.2              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Galaxy Container, ABF Equity | Transportation                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30] 0.2                  
Fair Value, ending balance 0.2 [1],[4],[18],[28],[29]   0.2 [2],[3],[17],[26],[30]              
Investment, Identifier [Axis]: Galaxy Container, Bond                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0                  
Gross Additions [11] 0.2                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 0.0                  
Fair Value, ending balance 0.2   0.0              
Investment Income [15] 0.0                  
PIK Income [15] 0.0                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: Galaxy Container, Bond | Transportation                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28] 0.2                  
Investment, Identifier [Axis]: Galaxy Universal LLC 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 86.3 86.3              
Gross Additions [6]     0.0              
Gross Reductions [8]     (86.3)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.0              
Fair Value, ending balance     0.0              
Investment Income [10]     9.4              
PIK Income [10]     0.0              
Fee income [10]     0.2              
Dividend and Other Income [10]     0.0              
Investment, Identifier [Axis]: Galaxy Universal LLC 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 18.5 18.5              
Gross Additions [6]     1.9              
Gross Reductions [8]     (20.4)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.0              
Fair Value, ending balance     0.0              
Investment Income [10]     2.1              
PIK Income [10]     0.0              
Fee income [10]     0.1              
Dividend and Other Income [10]     0.0              
Investment, Identifier [Axis]: Galaxy Universal LLC 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions [6]     45.5              
Gross Reductions [8]     (45.5)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.0              
Fair Value, ending balance     0.0              
Investment Income [10]     4.5              
PIK Income [10]     0.0              
Fee income [10]     2.0              
Dividend and Other Income [10]     0.0              
Investment, Identifier [Axis]: Galaxy Universal LLC 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions [6]     37.5              
Gross Reductions [8]     (37.5)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.0              
Fair Value, ending balance     0.0              
Investment Income [10]     3.1              
PIK Income [10]     0.0              
Fee income [10]     1.1              
Dividend and Other Income [10]     0.0              
Investment, Identifier [Axis]: Galaxy Universal LLC | Consumer Durables & Apparel 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 121.3                  
Fair Value, ending balance 120.6 [1],[4],[18]   121.3 [2],[3],[17]              
Investment, Identifier [Axis]: Galaxy Universal LLC | Consumer Durables & Apparel 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 64.4                  
Fair Value, ending balance 19.8 [1],[4],[18]   64.4 [2],[3],[17]              
Investment, Identifier [Axis]: Galaxy Universal LLC | Consumer Durables & Apparel 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 39.2                  
Fair Value, ending balance 43.9 [1],[4],[18]   39.2 [2],[3],[17]              
Investment, Identifier [Axis]: Galaxy Universal LLC | Consumer Durables & Apparel 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 11.2                  
Fair Value, ending balance 49.8 [1],[4],[18]   11.2 [2],[3],[21]              
Investment, Identifier [Axis]: Galaxy Universal LLC, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 49.2 49.2              
Gross Additions [6]     0.0              
Gross Reductions [8]     (43.9)              
Net Realized Gain (Loss)     8.5              
Net Change in Unrealized Appreciation (Depreciation)     (13.8)              
Fair Value, ending balance     0.0              
Investment Income [10]     0.0              
PIK Income [10]     0.0              
Fee income [10]     0.0              
Dividend and Other Income [10]     0.0              
Investment, Identifier [Axis]: Galaxy Universal LLC, Common Stock | Consumer Durables & Apparel                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[26],[47] 0.2                  
Fair Value, ending balance 0.1 [1],[4],[29],[49]   0.2 [2],[3],[26],[47]              
Investment, Identifier [Axis]: Galaxy Universal LLC, Preferred Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 7.2 7.2              
Gross Additions [6]     0.7              
Gross Reductions [8]     (5.6)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     (2.3)              
Fair Value, ending balance     0.0              
Investment Income [10]     0.0              
PIK Income [10]     0.8              
Fee income [10]     0.0              
Dividend and Other Income [10]     0.0              
Investment, Identifier [Axis]: Galaxy Universal LLC, Preferred Stock | Consumer Durables & Apparel 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[26],[47] 6.1                  
Fair Value, ending balance 6.1 [1],[4],[29],[49]   6.1 [2],[3],[26],[47]              
Investment, Identifier [Axis]: Galaxy Universal LLC, Preferred Stock | Consumer Durables & Apparel 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[26],[47] 8.7                  
Fair Value, ending balance 9.7 [1],[4],[29],[49]   8.7 [2],[26],[47]              
Investment, Identifier [Axis]: Galaxy Universal LLC, Trade Claim                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 1.9 1.9              
Gross Additions [6]     0.0              
Gross Reductions [8]     (2.5)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.6              
Fair Value, ending balance     0.0              
Investment Income [10]     0.0              
PIK Income [10]     0.0              
Fee income [10]     0.0              
Dividend and Other Income [10]     0.0              
Investment, Identifier [Axis]: Galaxy Universal LLC, Trade Claim | Consumer Durables & Apparel                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26] 0.5                  
Fair Value, ending balance 0.5 [1],[4],[18],[29]   0.5 [2],[17],[26]              
Investment, Identifier [Axis]: Galway Partners Holdings LLC | Insurance 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 2.3                  
Fair Value, ending balance 4.9 [1],[4],[18]   2.3 [2],[3],[17]              
Investment, Identifier [Axis]: Galway Partners Holdings LLC | Insurance 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39],[40],[44] 77.9                  
Fair Value, ending balance 78.1 [1],[4],[18],[34],[37],[41],[45]   77.9 [2],[3],[17],[33],[39],[40],[44]              
Investment, Identifier [Axis]: Galway Partners Holdings LLC | Insurance 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 10.7                  
Fair Value, ending balance 8.1 [1],[4],[22]   10.7 [2],[3],[21]              
Investment, Identifier [Axis]: Galway Partners Holdings LLC | Insurance 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 6.7                  
Fair Value, ending balance [2],[3],[21]     6.7              
Investment, Identifier [Axis]: General Datatech LP | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39],[40] 109.6                  
Fair Value, ending balance 104.5 [1],[4],[18],[34],[37],[41]   109.6 [2],[3],[17],[33],[39],[40]              
Investment, Identifier [Axis]: Gigamon Inc | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 3.7                  
Fair Value, ending balance 98.1 [1],[4],[18],[20]   3.7 [2],[3],[17]              
Investment, Identifier [Axis]: Gigamon Inc | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[19] 101.9                  
Fair Value, ending balance 8.8 [1],[4],[22]   101.9 [2],[3],[17],[19]              
Investment, Identifier [Axis]: Gigamon Inc | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 5.5                  
Fair Value, ending balance [2],[3],[21]     5.5              
Investment, Identifier [Axis]: Global Jet Capital LLC, Preferred Stock | Commercial & Professional Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[50],[55] 206.9                  
Fair Value, ending balance 204.3 [1],[4],[18],[29],[51],[56]   206.9 [2],[3],[17],[26],[50],[55]              
Investment, Identifier [Axis]: Gracent LLC                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 28.4 29.6 29.6              
Gross Additions (0.1) [11]   4.7 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (1.5)   (5.9)              
Fair Value, ending balance 26.8   28.4              
Investment Income 0.0 [15]   1.0 [16]              
PIK Income 0.0 [15]   3.7 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Gracent LLC | Health Care Equipment & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[27],[30] 28.4                  
Fair Value, ending balance 26.8 [1],[4],[18],[28],[29],[32]   28.4 [2],[3],[17],[26],[27],[30]              
Investment, Identifier [Axis]: Gracent LLC, Class A Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Gracent LLC, Class A Common Stock | Health Care Equipment & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[26],[30],[47] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[28],[29],[49]   0.0 [2],[26],[30],[47]              
Investment, Identifier [Axis]: Gracent LLC, Preferred Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 5.0 5.0              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) (8.2)   0.0              
Net Change in Unrealized Appreciation (Depreciation) 8.2   (5.0)              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Gracent LLC, Preferred Equity | Health Care Equipment & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[26],[30],[47] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[28],[29],[49]   0.0 [2],[26],[30],[47]              
Investment, Identifier [Axis]: Gracent LLC, Preferred Stock B                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Gracent LLC, Preferred Stock B | Health Care Equipment & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[26],[30],[47] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[28],[29],[49]   0.0 [2],[26],[30],[47]              
Investment, Identifier [Axis]: Granicus Inc | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[39] 16.5                  
Fair Value, ending balance 16.6 [1],[4],[18],[37]   16.5 [2],[3],[17],[39]              
Investment, Identifier [Axis]: Granicus Inc | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[39] 5.6                  
Fair Value, ending balance 5.6 [1],[4],[18],[37]   5.6 [2],[3],[17],[39]              
Investment, Identifier [Axis]: Granicus Inc | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 2.3                  
Fair Value, ending balance 2.3 [1],[4],[22]   2.3 [2],[3],[21]              
Investment, Identifier [Axis]: Granicus Inc | Software & Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 0.5                  
Fair Value, ending balance 0.5 [1],[4],[22]   0.5 [2],[3],[21]              
Investment, Identifier [Axis]: GreenSky Holdings LLC, ABF Equity 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 14.5 14.9 14.9              
Gross Additions 0.0 [5]   0.0 [6]              
Gross Reductions 0.0 [7]   0.0 [8]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.4   (0.4)              
Fair Value, ending balance 14.9   14.5              
Investment Income 0.0 [9]   0.0 [10]              
PIK Income 0.0 [9]   0.0 [10]              
Fee income 0.0 [9]   0.0 [10]              
Dividend and Other Income 0.0 [9]   0.0 [10]              
Investment, Identifier [Axis]: GreenSky Holdings LLC, ABF Equity 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 15.3 22.3 22.3              
Gross Additions 0.0 [5]   2.6 [6]              
Gross Reductions (1.8) [7]   (8.4) [8]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.9   (1.2)              
Fair Value, ending balance 14.4   15.3              
Investment Income 0.0 [9]   0.0 [10]              
PIK Income 0.0 [9]   0.0 [10]              
Fee income 0.0 [9]   0.0 [10]              
Dividend and Other Income 0.4 [9]   3.6 [10]              
Investment, Identifier [Axis]: GreenSky Holdings LLC, ABF Equity | Financial Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25],[26] 14.5                  
Fair Value, ending balance 14.9 [1],[4],[18],[29],[38]   14.5 [2],[3],[17],[25],[26]              
Investment, Identifier [Axis]: GreenSky Holdings LLC, ABF Equity | Financial Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25],[31] 15.3                  
Fair Value, ending balance 14.4 [1],[4],[18],[36],[38]   15.3 [2],[3],[17],[25],[31]              
Investment, Identifier [Axis]: GreenSky Holdings LLC, Term Loan                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 36.7 33.5 33.5              
Gross Additions 0.0 [5]   3.2 [6]              
Gross Reductions (3.6) [7]   0.0 [8]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 33.1   36.7              
Investment Income 0.0 [9]   0.0 [10]              
PIK Income 0.8 [9]   3.4 [10]              
Fee income 0.0 [9]   0.0 [10]              
Dividend and Other Income 0.0 [9]   0.0 [10]              
Investment, Identifier [Axis]: GreenSky Holdings LLC, Term Loan | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[38] 33.1                  
Investment, Identifier [Axis]: GreenSky Holdings LLC, Term Loan | Financial Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25] 36.7                  
Fair Value, ending balance [2],[3],[17],[25]     36.7              
Investment, Identifier [Axis]: GreenSky Holdings LLC, Term Loan | Financial Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[25] 3.0                  
Fair Value, ending balance [2],[3],[21],[25]     3.0              
Investment, Identifier [Axis]: HM Dunn Co Inc 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 19.2 34.8 34.8              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   (13.1) [14]              
Net Realized Gain (Loss) 0.0   (2.5)              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 19.2   19.2              
Investment Income 0.5 [15]   2.8 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: HM Dunn Co Inc 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 4.0 3.4 3.4              
Gross Additions 1.0 [11]   2.6 [12]              
Gross Reductions 0.0 [13]   (2.0) [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 5.0   4.0              
Investment Income 0.1 [15]   0.5 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: HM Dunn Co Inc | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30] 19.2                  
Fair Value, ending balance 19.2 [1],[4],[18],[28]   19.2 [2],[3],[17],[30]              
Investment, Identifier [Axis]: HM Dunn Co Inc | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30] 4.0                  
Fair Value, ending balance 5.0 [1],[4],[18],[28]   4.0 [2],[3],[17],[30]              
Investment, Identifier [Axis]: HM Dunn Co Inc | Capital Goods 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[30] 6.0                  
Fair Value, ending balance 5.0 [1],[4],[22],[28]   6.0 [2],[3],[21],[30]              
Investment, Identifier [Axis]: HM Dunn Co Inc, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.4                  
Gross Additions [11] 0.0                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 1.2                  
Fair Value, ending balance 1.6   0.4              
Investment Income [15] 0.0                  
PIK Income [15] 0.0                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: HM Dunn Co Inc, Common Stock | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26],[30],[35] 0.4                  
Fair Value, ending balance 1.6 [1],[4],[18],[28],[29]   0.4 [2],[17],[26],[30],[35]              
Investment, Identifier [Axis]: HM Dunn Co Inc, Preferred Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 15.6                  
Gross Additions [11] 0.5                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 1.9                  
Fair Value, ending balance 18.0   15.6              
Investment Income [15] 0.0                  
PIK Income [15] 0.6                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: HM Dunn Co Inc, Preferred Equity | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[30] 15.6                  
Fair Value, ending balance 18.0 [1],[4],[18],[28]   15.6 [2],[17],[30]              
Investment, Identifier [Axis]: HM Dunn Co Inc, Preferred Stock, Series A                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.1 0.1              
Gross Additions [12]     0.0              
Gross Reductions [14]     0.0              
Net Realized Gain (Loss)     (7.1)              
Net Change in Unrealized Appreciation (Depreciation)     7.0              
Fair Value, ending balance     0.0              
Investment Income [16]     0.0              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: HM Dunn Co Inc, Preferred Stock, Series B                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions [12]     0.0              
Gross Reductions [14]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.0              
Fair Value, ending balance     0.0              
Investment Income [16]     0.0              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Hargreaves Lansdown Ltd | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 29.1                  
Fair Value, ending balance 28.3 [1],[4],[18],[36]   29.1 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Harley-Davidson Financial Services Inc, ABF Equity | Financial Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 7.8                  
Fair Value, ending balance 7.7 [1],[4],[18],[36]   7.8 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Harley-Davidson Financial Services Inc, ABF Equity | Financial Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 27.0                  
Fair Value, ending balance 26.4 [1],[4],[18],[36]   27.0 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Harley-Davidson Financial Services Inc, ABF Equity | Financial Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[31] 1.9                  
Fair Value, ending balance 1.9 [1],[4],[18],[29],[36]   1.9 [2],[3],[17],[26],[31]              
Investment, Identifier [Axis]: Heniff Transportation Systems LLC | Transportation 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 67.9                  
Fair Value, ending balance 60.6 [1],[4],[18]   67.9 [2],[3],[17]              
Investment, Identifier [Axis]: Heniff Transportation Systems LLC | Transportation 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 14.1                  
Fair Value, ending balance 15.1 [1],[4],[18]   14.1 [2],[3],[17]              
Investment, Identifier [Axis]: Heniff Transportation Systems LLC | Transportation 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[39] 12.4                  
Fair Value, ending balance 11.0 [1],[4],[18],[37]   12.4 [2],[3],[17],[39]              
Investment, Identifier [Axis]: Heniff Transportation Systems LLC | Transportation 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.3                  
Fair Value, ending balance 0.5 [1],[4],[22]   3.3 [2],[3],[21]              
Investment, Identifier [Axis]: Hibu Inc | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[39],[40],[44] 105.9                  
Fair Value, ending balance 104.4 [1],[4],[18],[37],[41],[45]   105.9 [2],[3],[17],[39],[40],[44]              
Investment, Identifier [Axis]: Hibu Inc | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33] 18.9                  
Fair Value, ending balance 35.1 [1],[4],[18],[34]   18.9 [2],[3],[17],[33]              
Investment, Identifier [Axis]: Hibu Inc | Commercial & Professional Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 16.8                  
Fair Value, ending balance [2],[3],[17]     16.8              
Investment, Identifier [Axis]: Higginbotham Insurance Agency Inc | Insurance 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[52] 6.0                  
Fair Value, ending balance 5.9 [1],[4],[18]   6.0 [2],[3],[17],[52]              
Investment, Identifier [Axis]: Higginbotham Insurance Agency Inc | Insurance 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[52] 1.0                  
Fair Value, ending balance 1.0 [1],[4],[22]   1.0 [2],[3],[21],[52]              
Investment, Identifier [Axis]: Highgate Hotels Inc | Consumer Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 33.3                  
Fair Value, ending balance 33.2 [1],[4],[18],[34],[37]   33.3 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Highgate Hotels Inc | Consumer Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 4.2                  
Fair Value, ending balance 1.4 [1],[4],[18]   4.2 [2],[3],[21]              
Investment, Identifier [Axis]: Highgate Hotels Inc | Consumer Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 4.0                  
Fair Value, ending balance 2.8 [1],[4],[22]   4.0 [2],[3],[21]              
Investment, Identifier [Axis]: Highgate Hotels Inc | Consumer Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22] 3.9                  
Investment, Identifier [Axis]: Homrich & Berg Inc | Financial Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 0.8                  
Fair Value, ending balance 1.0 [1],[4],[18]   0.8 [2],[3],[17]              
Investment, Identifier [Axis]: Homrich & Berg Inc | Financial Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33] 6.3                  
Fair Value, ending balance 6.3 [1],[4],[18],[34]   6.3 [2],[3],[17],[33]              
Investment, Identifier [Axis]: Homrich & Berg Inc | Financial Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 0.7                  
Fair Value, ending balance 1.0 [1],[4],[18]   0.7 [2],[3],[21]              
Investment, Identifier [Axis]: Homrich & Berg Inc | Financial Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22] 0.5                  
Investment, Identifier [Axis]: Homrich & Berg Inc | Financial Services 5                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22] 6.2                  
Investment, Identifier [Axis]: Horizon CTS Buyer LLC | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39],[40] 86.5                  
Fair Value, ending balance 86.2 [1],[4],[18],[34],[37],[41]   86.5 [2],[3],[17],[33],[39],[40]              
Investment, Identifier [Axis]: Horizon CTS Buyer LLC | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 3.2                  
Fair Value, ending balance 3.2 [1],[4],[18]   3.2 [2],[3],[17]              
Investment, Identifier [Axis]: Horizon CTS Buyer LLC | Capital Goods 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[44] 5.4                  
Fair Value, ending balance 5.4 [1],[4],[45]   5.4 [2],[3],[44]              
Investment, Identifier [Axis]: Horizon CTS Buyer LLC | Capital Goods 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 15.1                  
Fair Value, ending balance 15.1 [1],[4],[22]   15.1 [2],[3],[21]              
Investment, Identifier [Axis]: Horizon CTS Buyer LLC | Capital Goods 5                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 2.2                  
Fair Value, ending balance 2.2 [1],[4],[22]   2.2 [2],[3],[21]              
Investment, Identifier [Axis]: Industria Chimica Emiliana Srl | Pharmaceuticals, Biotechnology & Life Sciences                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 87.1                  
Fair Value, ending balance 84.9 [4],[18],[36]   87.1 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Industry City TI Lessor LP | Consumer Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[35] 9.9                  
Fair Value, ending balance 8.1 [4],[18]   9.9 [2],[3],[17],[35]              
Investment, Identifier [Axis]: Inhabit IQ | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.6                  
Fair Value, ending balance 3.6 [4],[22]   3.6 [2],[3],[21]              
Investment, Identifier [Axis]: Inhabit IQ | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 2.3                  
Fair Value, ending balance 2.2 [4],[22]   2.3 [2],[3],[21]              
Investment, Identifier [Axis]: Insight Global LLC | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[19],[33],[39] 62.4                  
Fair Value, ending balance 62.2 [4],[18],[20],[34],[37]   62.4 [2],[3],[17],[19],[33],[39]              
Investment, Identifier [Axis]: Insight Global LLC | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 36.6                  
Fair Value, ending balance 36.6 [4],[22]   36.6 [2],[3],[21]              
Investment, Identifier [Axis]: Insightsoftware.Com Inc | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 2.8                  
Fair Value, ending balance 2.7 [4],[18]   2.8 [2],[3],[17]              
Investment, Identifier [Axis]: Insightsoftware.Com Inc | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 2.0                  
Fair Value, ending balance 2.7 [4],[18]   2.0 [2],[3],[17]              
Investment, Identifier [Axis]: Insightsoftware.Com Inc | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 41.1                  
Fair Value, ending balance 39.3 [4],[18],[34],[37]   41.1 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Insightsoftware.Com Inc | Software & Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 25.8                  
Fair Value, ending balance 20.2 [4],[22]   25.8 [2],[3],[21]              
Investment, Identifier [Axis]: Insightsoftware.Com Inc | Software & Services 5                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.4                  
Fair Value, ending balance 2.4 [4],[22]   3.4 [2],[3],[21]              
Investment, Identifier [Axis]: Integrated Power Services LLC | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [4],[18],[45] 17.9                  
Investment, Identifier [Axis]: Integrated Power Services LLC | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [4],[22] 4.4                  
Investment, Identifier [Axis]: Integrated Power Services LLC | Commercial & Professional Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [4],[22] 9.0                  
Investment, Identifier [Axis]: Integrity Marketing Group LLC | Insurance 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 98.5                  
Fair Value, ending balance 98.2 [4],[18],[34],[37]   98.5 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Integrity Marketing Group LLC | Insurance 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 0.1                  
Fair Value, ending balance 0.1 [4],[22]   0.1 [2],[3],[21]              
Investment, Identifier [Axis]: Integrity Marketing Group LLC | Insurance 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 0.7                  
Fair Value, ending balance 0.7 [4],[22]   0.7 [2],[3],[21]              
Investment, Identifier [Axis]: J S Held LLC | Insurance 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39],[44] 82.8                  
Fair Value, ending balance 3.5 [4],[18]   82.8 [2],[3],[17],[33],[39],[44]              
Investment, Identifier [Axis]: J S Held LLC | Insurance 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 9.2                  
Fair Value, ending balance 79.5 [4],[18],[34],[37],[45]   9.2 [2],[3],[17]              
Investment, Identifier [Axis]: J S Held LLC | Insurance 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 6.9                  
Fair Value, ending balance 3.5 [4],[22]   6.9 [2],[3],[21]              
Investment, Identifier [Axis]: J S Held LLC | Insurance 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 10.8                  
Fair Value, ending balance 8.9 [4],[22]   10.8 [2],[3],[21]              
Investment, Identifier [Axis]: JW Aluminum Co                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 76.6 76.6              
Gross Additions [12]     0.0              
Gross Reductions [14]     (76.4)              
Net Realized Gain (Loss)     0.3              
Net Change in Unrealized Appreciation (Depreciation)     (0.5)              
Fair Value, ending balance     0.0              
Investment Income [16]     1.9              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: JW Aluminum Co, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 2.5 2.5              
Gross Additions [12]     0.0              
Gross Reductions [14]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     (2.5)              
Fair Value, ending balance     0.0              
Investment Income [16]     0.0              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: JW Aluminum Co, Preferred Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 170.4                  
Gross Additions [11] 0.0                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 34.2                  
Fair Value, ending balance 204.6   170.4              
Investment Income [15] 0.0                  
PIK Income [15] 0.0                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: JW Aluminum Co, Preferred Stock 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 152.3 152.3              
Gross Additions [12]     0.0              
Gross Reductions [14]     (156.4)              
Net Realized Gain (Loss)     (58.1)              
Net Change in Unrealized Appreciation (Depreciation)     62.2              
Fair Value, ending balance     0.0              
Investment Income [16]     0.0              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: JW Aluminum Co, Preferred Stock 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 170.4 0.0 0.0              
Gross Additions [12]     135.2              
Gross Reductions [14]     (10.4)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     45.6              
Fair Value, ending balance     170.4              
Investment Income [16]     0.0              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     14.3              
Investment, Identifier [Axis]: JW Aluminum Co, Preferred Stock | Materials                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[30],[50],[55] 170.4                  
Fair Value, ending balance 204.6 [1],[4],[18],[28],[51],[56]   170.4 [2],[17],[30],[50],[55]              
Investment, Identifier [Axis]: Jeppesen Holdings LLC | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 2.4                  
Fair Value, ending balance 2.4 [4],[22],[36]   2.4 [2],[3],[21],[31]              
Investment, Identifier [Axis]: KKR Altitude II Offshore Aggregator LP, Partnership Interest                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 115.7 146.7 146.7              
Gross Additions 0.0 [11]   27.6 [12]              
Gross Reductions 0.0 [13]   (62.0) [14]              
Net Realized Gain (Loss) 0.0   3.9              
Net Change in Unrealized Appreciation (Depreciation) 0.3   (0.5)              
Fair Value, ending balance 116.0   115.7              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 3.1 [15]   15.2 [16]              
Investment, Identifier [Axis]: KKR Altitude II Offshore Aggregator LP, Partnership Interest | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 115.7                  
Fair Value, ending balance 116.0 [1],[4],[18],[28],[36]   115.7 [2],[3],[17],[30],[31]              
Investment, Identifier [Axis]: KKR Central Park Leasing Aggregator L.P., Partnership Interest                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 27.0 15.8 15.8              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   11.2              
Fair Value, ending balance 27.0   27.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: KKR Central Park Leasing Aggregator L.P., Partnership Interest | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[27],[30],[31] 27.0                  
Fair Value, ending balance 27.0 [1],[4],[18],[28],[29],[36]   27.0 [2],[3],[17],[26],[27],[30],[31]              
Investment, Identifier [Axis]: KKR Chord IP Aggregator LP, Partnership Interest                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.1 0.1 0.1              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 0.1   0.1              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.2 [16]              
Investment, Identifier [Axis]: KKR Chord IP Aggregator LP, Partnership Interest | Media & Entertainment                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 0.1                  
Fair Value, ending balance 0.1 [1],[4],[18],[28],[36]   0.1 [2],[3],[17],[30],[31]              
Investment, Identifier [Axis]: KKR Rocket Loans Aggregator LLC, Partnership Interest                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 2.0 4.3 4.3              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions (0.2) [13]   (2.9) [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (0.1)   0.6              
Fair Value, ending balance 1.7   2.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: KKR Rocket Loans Aggregator LLC, Partnership Interest | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30],[31] 2.0                  
Fair Value, ending balance 1.7 [1],[4],[18],[28],[29],[36]   2.0 [2],[3],[17],[26],[30],[31]              
Investment, Identifier [Axis]: KKR Zeno Aggregator LP (K2 Aviation), Partnership Interest                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 1.0 7.2 7.2              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   (2.9) [14]              
Net Realized Gain (Loss) 0.0   0.3              
Net Change in Unrealized Appreciation (Depreciation) (0.8)   (3.6)              
Fair Value, ending balance 0.2   1.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 1.2 [15]   7.2 [16]              
Investment, Identifier [Axis]: KKR Zeno Aggregator LP (K2 Aviation), Partnership Interest | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 1.0                  
Fair Value, ending balance 0.2 [1],[4],[18],[28],[36]   1.0 [2],[3],[17],[30],[31]              
Investment, Identifier [Axis]: KSC I Aircraft LP, ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 5.8 0.0 0.0              
Gross Additions 4.3 [11]   5.8 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 10.1   5.8              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: KSC I Aircraft LP, ABF Equity | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30],[31] 5.8                  
Fair Value, ending balance 10.1 [1],[4],[18],[28],[29],[36]   5.8 [2],[3],[17],[26],[30],[31]              
Investment, Identifier [Axis]: Kellermeyer Bergensons Services LLC 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 220.3 201.6 201.6              
Gross Additions 5.4 [11]   21.5 [12]              
Gross Reductions (0.5) [13]   (1.9) [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (0.2)   (0.9)              
Fair Value, ending balance 225.0   220.3              
Investment Income 0.0 [15]   0.8 [16]              
PIK Income 5.3 [15]   20.7 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Kellermeyer Bergensons Services LLC 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 40.3 87.7 87.7              
Gross Additions 0.1 [11]   5.9 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (27.3)   (53.3)              
Fair Value, ending balance 13.1   40.3              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   3.9 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Kellermeyer Bergensons Services LLC | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[35] 220.3                  
Fair Value, ending balance 225.0 [4],[18],[28]   220.3 [2],[3],[17],[30],[35]              
Investment, Identifier [Axis]: Kellermeyer Bergensons Services LLC | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[27],[30],[35] 40.3                  
Fair Value, ending balance 13.1 [4],[18],[28],[29],[32]   40.3 [2],[3],[17],[26],[27],[30],[35]              
Investment, Identifier [Axis]: Kellermeyer Bergensons Services LLC, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Kellermeyer Bergensons Services LLC, Common Stock | Commercial & Professional Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26],[30],[35] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[28],[29]   0.0 [2],[17],[26],[30],[35]              
Investment, Identifier [Axis]: Kellermeyer Bergensons Services LLC, Preferred Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 15.1 15.1              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   (15.1)              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Kellermeyer Bergensons Services LLC, Preferred Stock | Commercial & Professional Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26],[30],[35] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[28],[29]   0.0 [2],[17],[26],[30],[35]              
Investment, Identifier [Axis]: Kestra Financial Inc, Preferred Equity | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18] 2.1                  
Investment, Identifier [Axis]: Kestra Financial Inc, Preferred Equity | Financial Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17] 2.0                  
Fair Value, ending balance [2],[17]     2.0              
Investment, Identifier [Axis]: Kestra Financial Inc, Preferred Equity | Financial Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[21] 9.2                  
Fair Value, ending balance [2],[21]     9.2              
Investment, Identifier [Axis]: Keystone Agency Partners LLC | Insurance 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33] 33.1                  
Fair Value, ending balance 33.1 [4],[18],[34],[37]   33.1 [2],[3],[17],[33]              
Investment, Identifier [Axis]: Keystone Agency Partners LLC | Insurance 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 8.5                  
Fair Value, ending balance 8.5 [4],[22]   8.5 [2],[3],[21]              
Investment, Identifier [Axis]: Keystone Agency Partners LLC | Insurance 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.8                  
Fair Value, ending balance 3.8 [4],[22]   3.8 [2],[3],[21]              
Investment, Identifier [Axis]: Kilter Finance 2.0, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0                  
Gross Additions [11] 4.0                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 0.0                  
Fair Value, ending balance 4.0   0.0              
Investment Income [15] 0.0                  
PIK Income [15] 0.0                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: Kilter Finance 2.0, Common Stock | Insurance                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[29],[36] 4.0                  
Investment, Identifier [Axis]: Kilter Finance, ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 3.0 0.5 0.5              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (0.3)   2.5              
Fair Value, ending balance 2.7   3.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Kilter Finance, ABF Equity | Insurance                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30],[31] 3.0                  
Fair Value, ending balance 2.7 [1],[4],[18],[28],[29],[36]   3.0 [2],[3],[17],[26],[30],[31]              
Investment, Identifier [Axis]: Kilter Finance, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Kilter Finance, Common Stock | Insurance                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30],[31] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[28],[29],[36]   0.0 [2],[3],[17],[26],[30],[31]              
Investment, Identifier [Axis]: Kilter Finance, Preferred Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 88.4 85.4 85.4              
Gross Additions 0.8 [11]   18.6 [12]              
Gross Reductions 0.0 [13]   (15.6) [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 89.2   88.4              
Investment Income 1.9 [15]   6.1 [16]              
PIK Income 0.8 [15]   3.8 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Kilter Finance, Preferred Stock | Insurance                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 88.4                  
Fair Value, ending balance 89.2 [1],[4],[18],[28],[36]   88.4 [2],[3],[17],[30],[31]              
Investment, Identifier [Axis]: Laboratoires Vivacy SAS | Pharmaceuticals, Biotechnology & Life Sciences 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 0.1                  
Fair Value, ending balance 0.1 [4],[18],[36]   0.1 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Laboratoires Vivacy SAS | Pharmaceuticals, Biotechnology & Life Sciences 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 0.5                  
Fair Value, ending balance 0.5 [4],[22],[36]   0.5 [2],[3],[21],[31]              
Investment, Identifier [Axis]: Lazer Logistics Inc | Transportation 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 1.7                  
Fair Value, ending balance 6.9 [4],[18],[34]   1.7 [2],[3],[17]              
Investment, Identifier [Axis]: Lazer Logistics Inc | Transportation 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 24.1                  
Fair Value, ending balance 20.0 [4],[18],[34],[37]   24.1 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Lazer Logistics Inc | Transportation 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 1.9                  
Fair Value, ending balance 1.9 [4],[22]   1.9 [2],[3],[21]              
Investment, Identifier [Axis]: Lazer Logistics Inc | Transportation 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 2.4                  
Fair Value, ending balance 1.2 [4],[22]   2.4 [2],[3],[21]              
Investment, Identifier [Axis]: Learning Experience Corp/The | Consumer Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[40] 16.0                  
Fair Value, ending balance 16.0 [4],[41]   16.0 [2],[3],[40]              
Investment, Identifier [Axis]: Learning Experience Corp/The | Consumer Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.5                  
Fair Value, ending balance 3.5 [4],[22]   3.5 [2],[3],[21]              
Investment, Identifier [Axis]: Legends Hospitality LLC | Consumer Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 4.5                  
Fair Value, ending balance 7.2 [4],[18]   4.5 [2],[3],[17]              
Investment, Identifier [Axis]: Legends Hospitality LLC | Consumer Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[40],[44] 78.4                  
Fair Value, ending balance 79.0 [1],[4],[18],[41],[45]   78.4 [2],[3],[17],[40],[44]              
Investment, Identifier [Axis]: Legends Hospitality LLC | Consumer Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 9.3                  
Fair Value, ending balance 6.5 [1],[4],[22]   9.3 [2],[3],[21]              
Investment, Identifier [Axis]: Legends Hospitality LLC | Consumer Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 1.2                  
Fair Value, ending balance [2],[3],[21]     1.2              
Investment, Identifier [Axis]: Leia Acquisition Ltd. (fka Swift Worldwide Resources Holdco Ltd) , Commercial & Professional Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 0.1                  
Fair Value, ending balance [2],[3],[17]     0.1              
Investment, Identifier [Axis]: Leia Acquisition Ltd. (fka Swift Worldwide Resources Holdco Ltd) | Commercial & Professional Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18] 0.2                  
Investment, Identifier [Axis]: Lido Advisors LLC, Class A Common Stock | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[26],[31],[47] 4.7                  
Fair Value, ending balance 5.5 [1],[4],[29],[36],[49]   4.7 [2],[26],[31],[47]              
Investment, Identifier [Axis]: Lido Advisors LLC, Class Z Preferred Stock | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[26],[31],[47] 5.2                  
Fair Value, ending balance 5.5 [1],[4],[29],[36],[49]   5.2 [2],[26],[31],[47]              
Investment, Identifier [Axis]: Lionbridge Technologies Inc 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0                  
Gross Additions [11] 55.5                  
Gross Reductions [13] (5.6)                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 0.0                  
Fair Value, ending balance 49.9   0.0              
Investment Income [15] 0.0                  
PIK Income [15] 0.8                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: Lionbridge Technologies Inc 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0                  
Gross Additions [11] 53.8                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) (27.9)                  
Fair Value, ending balance 25.9   0.0              
Investment Income [15] 0.0                  
PIK Income [15] 0.0                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: Lionbridge Technologies Inc | Media & Entertainment                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[19],[26],[27],[35] 79.0                  
Fair Value, ending balance [2],[3],[17],[19],[26],[27],[35]     79.0              
Investment, Identifier [Axis]: Lionbridge Technologies Inc | Media & Entertainment 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[20],[28] 49.9                  
Investment, Identifier [Axis]: Lionbridge Technologies Inc | Media & Entertainment 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[20],[28],[29],[32] 25.9                  
Investment, Identifier [Axis]: Lionbridge Technologies Inc | Media & Entertainment 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22],[28] 5.5                  
Investment, Identifier [Axis]: Lionbridge Technologies Inc, Common Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0                  
Gross Additions [11] 0.0                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 0.0                  
Fair Value, ending balance 0.0   0.0              
Investment Income [15] 0.0                  
PIK Income [15] 0.0                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: Lionbridge Technologies Inc, Common Equity | Media & Entertainment                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[29] 0.0                  
Investment, Identifier [Axis]: Lionbridge Technologies Inc, Preferred Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0                  
Gross Additions [11] 0.0                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 0.0                  
Fair Value, ending balance 0.0   0.0              
Investment Income [15] 0.0                  
PIK Income [15] 0.0                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: Lionbridge Technologies Inc, Preferred Stock | Media & Entertainment                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[29] 0.0                  
Investment, Identifier [Axis]: Lipari Foods LLC | Consumer Staples Distribution & Retail                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[19] 95.5                  
Fair Value, ending balance 98.3 [1],[4],[18],[20]   95.5 [2],[3],[17],[19]              
Investment, Identifier [Axis]: Lipari Foods LLC, Common Stock | Consumer Staples Distribution & Retail                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26] 3.2                  
Fair Value, ending balance 4.1 [1],[4],[18],[29]   3.2 [2],[17],[26]              
Investment, Identifier [Axis]: Lloyd's Register Quality Assurance Ltd | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 20.2                  
Fair Value, ending balance [2],[3],[17],[31]     20.2              
Investment, Identifier [Axis]: Lloyd's Register Quality Assurance Ltd | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 7.5                  
Fair Value, ending balance [2],[3],[17],[31]     7.5              
Investment, Identifier [Axis]: Lloyd's Register Quality Assurance Ltd | Commercial & Professional Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 5.6                  
Fair Value, ending balance [2],[3],[21],[31]     5.6              
Investment, Identifier [Axis]: MAI Capital Management LLC | Financial Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 0.6                  
Fair Value, ending balance 1.2 [1],[4],[18]   0.6 [2],[3],[17]              
Investment, Identifier [Axis]: MAI Capital Management LLC | Financial Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 5.1                  
Fair Value, ending balance 6.3 [1],[4],[18]   5.1 [2],[3],[17]              
Investment, Identifier [Axis]: MAI Capital Management LLC | Financial Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 2.7                  
Fair Value, ending balance 2.1 [1],[4],[22]   2.7 [2],[3],[21]              
Investment, Identifier [Axis]: MAI Capital Management LLC | Financial Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 4.4                  
Fair Value, ending balance 3.1 [1],[4],[22]   4.4 [2],[3],[21]              
Investment, Identifier [Axis]: MB2 Dental Solutions LLC | Health Care Equipment & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39],[40],[44] 155.0                  
Fair Value, ending balance 157.9 [1],[4],[18],[34],[37],[41],[45]   155.0 [2],[3],[17],[33],[39],[40],[44]              
Investment, Identifier [Axis]: MB2 Dental Solutions LLC | Health Care Equipment & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 1.9                  
Fair Value, ending balance 0.4 [1],[4],[18]   1.9 [2],[3],[17]              
Investment, Identifier [Axis]: MB2 Dental Solutions LLC | Health Care Equipment & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 23.4                  
Fair Value, ending balance 10.3 [1],[4],[22]   23.4 [2],[3],[21]              
Investment, Identifier [Axis]: MB2 Dental Solutions LLC | Health Care Equipment & Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 8.8                  
Fair Value, ending balance [2],[3],[21]     8.8              
Investment, Identifier [Axis]: Magna Legal Services LLC | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 35.4                  
Fair Value, ending balance 22.9 [1],[4],[18],[34],[37]   35.4 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Magna Legal Services LLC | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 2.2                  
Fair Value, ending balance 12.4 [1],[4],[18]   2.2 [2],[3],[21]              
Investment, Identifier [Axis]: Magna Legal Services LLC | Commercial & Professional Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22] 2.2                  
Investment, Identifier [Axis]: Magna Legal Services LLC | Commercial & Professional Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22] 5.6                  
Investment, Identifier [Axis]: Magna Legal Services LLC, Common Stock | Commercial & Professional Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[26],[46] 9.1                  
Fair Value, ending balance 9.0 [1],[4],[29],[48]   9.1 [2],[26],[46]              
Investment, Identifier [Axis]: Med-Metrix | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[40],[44] 78.0                  
Fair Value, ending balance 77.4 [1],[4],[18],[34],[41],[45]   78.0 [2],[3],[17],[33],[40],[44]              
Investment, Identifier [Axis]: Med-Metrix | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 37.3                  
Fair Value, ending balance 36.7 [1],[4],[22]   37.3 [2],[3],[21]              
Investment, Identifier [Axis]: Med-Metrix | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 34.1                  
Fair Value, ending balance 33.8 [1],[4],[22]   34.1 [2],[3],[21]              
Investment, Identifier [Axis]: Med-Metrix, Common Stock | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26] 5.2                  
Fair Value, ending balance 5.2 [1],[4],[18],[29]   5.2 [2],[17],[26]              
Investment, Identifier [Axis]: Medallia Inc | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 184.7                  
Fair Value, ending balance 126.6 [1],[4],[18],[29],[32]   184.7 [2],[3],[17]              
Investment, Identifier [Axis]: Mercer Advisors Inc | Financial Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33] 42.8                  
Fair Value, ending balance 43.7 [1],[4],[18],[34]   42.8 [2],[3],[17],[33]              
Investment, Identifier [Axis]: Mercer Advisors Inc | Financial Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 4.5                  
Fair Value, ending balance 3.2 [1],[4],[22]   4.5 [2],[3],[21]              
Investment, Identifier [Axis]: Miami Beach Medical Group LLC, Common Stock | Health Care Equipment & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26] 7.5                  
Fair Value, ending balance 7.6 [1],[4],[18],[29]   7.5 [2],[17],[26]              
Investment, Identifier [Axis]: Misys Ltd, Preferred Stock | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[31] 53.8                  
Fair Value, ending balance 37.9 [1],[4],[18],[36]   53.8 [2],[17],[31]              
Investment, Identifier [Axis]: Model N Inc | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[39] 29.8                  
Fair Value, ending balance 29.2 [1],[4],[18],[37]   29.8 [2],[3],[17],[39]              
Investment, Identifier [Axis]: Model N Inc | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 6.2                  
Fair Value, ending balance 6.0 [1],[4],[22]   6.2 [2],[3],[21]              
Investment, Identifier [Axis]: Model N Inc | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.2                  
Fair Value, ending balance 3.2 [1],[4],[22]   3.2 [2],[3],[21]              
Investment, Identifier [Axis]: My Community Homes PropCo 2, ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 11.8 15.6 15.6              
Gross Additions 0.0 [11]   6.7 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (9.7)   (10.5)              
Fair Value, ending balance 2.1   11.8              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: My Community Homes PropCo 2, ABF Equity | Equity Real Estate Investment Trusts (REITs)                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30],[31] 11.8                  
Fair Value, ending balance 2.1 [1],[4],[18],[28],[29]   11.8 [2],[3],[17],[26],[30],[31]              
Investment, Identifier [Axis]: My Community Homes PropCo 2, Term Loan 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 69.4 64.4 64.4              
Gross Additions 1.3 [11]   5.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 70.7   69.4              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 1.3 [15]   5.1 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: My Community Homes PropCo 2, Term Loan 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 4.2 0.0 0.0              
Gross Additions 0.1 [11]   4.2 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 4.3   4.2              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.1 [15]   0.2 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: My Community Homes PropCo 2, Term Loan 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 22.3 0.0 0.0              
Gross Additions 0.4 [11]   22.3 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 22.7   22.3              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.4 [15]   0.9 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: My Community Homes PropCo 2, Term Loan | Equity Real Estate Investment Trusts (REITs) 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 69.4                  
Fair Value, ending balance 70.7 [1],[4],[18],[28]   69.4 [2],[3],[17],[30],[31]              
Investment, Identifier [Axis]: My Community Homes PropCo 2, Term Loan | Equity Real Estate Investment Trusts (REITs) 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 4.2                  
Fair Value, ending balance 4.3 [1],[4],[18],[28]   4.2 [2],[3],[17],[30],[31]              
Investment, Identifier [Axis]: My Community Homes PropCo 2, Term Loan | Equity Real Estate Investment Trusts (REITs) 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 22.3                  
Fair Value, ending balance 22.7 [1],[4],[18],[28]   22.3 [2],[3],[17],[30],[31]              
Investment, Identifier [Axis]: NAVEX Global Inc | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33] 14.6                  
Fair Value, ending balance 14.3 [1],[4],[18],[34]   14.6 [2],[3],[17],[33]              
Investment, Identifier [Axis]: NAVEX Global Inc | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 0.3                  
Fair Value, ending balance 0.3 [1],[4],[22]   0.3 [2],[3],[21]              
Investment, Identifier [Axis]: NAVEX Global Inc | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 6.7                  
Fair Value, ending balance 6.5 [1],[4],[22]   6.7 [2],[3],[21]              
Investment, Identifier [Axis]: NBG Home | Consumer Durables & Apparel 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26] 10.1                  
Fair Value, ending balance 10.1 [1],[4],[18],[29]   10.1 [2],[3],[17],[26]              
Investment, Identifier [Axis]: NBG Home | Consumer Durables & Apparel 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[27] 3.6                  
Fair Value, ending balance 3.7 [1],[4],[18],[29],[32]   3.6 [2],[3],[17],[26],[27]              
Investment, Identifier [Axis]: NCI Inc                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 30.7 32.1 32.1              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions (0.4) [13]   (1.4) [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.1   0.0              
Fair Value, ending balance 30.4   30.7              
Investment Income 0.5 [15]   3.8 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: NCI Inc | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30] 30.7                  
Fair Value, ending balance 30.4 [1],[4],[18],[28]   30.7 [2],[3],[17],[30]              
Investment, Identifier [Axis]: NCI Inc, Class A-1 Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: NCI Inc, Class A-1 Common Stock | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26],[30] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[28],[29]   0.0 [2],[17],[26],[30]              
Investment, Identifier [Axis]: NCI Inc, Class B-1 Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: NCI Inc, Class B-1 Common Stock | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26],[30] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[28],[29]   0.0 [2],[17],[26],[30]              
Investment, Identifier [Axis]: NCI Inc, Class C Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 38.7 33.1 33.1              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 6.7   5.6              
Fair Value, ending balance 45.4   38.7              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: NCI Inc, Class C Common Stock | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26],[30] 38.7                  
Fair Value, ending balance 45.4 [1],[4],[18],[28],[29]   38.7 [2],[17],[26],[30]              
Investment, Identifier [Axis]: NCI Inc, Class I-1 Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: NCI Inc, Class I-1 Common Stock | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26],[30] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[28],[29]   0.0 [2],[17],[26],[30]              
Investment, Identifier [Axis]: NEFCO Corp | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18] 22.6                  
Investment, Identifier [Axis]: NEFCO Corp | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18] 0.6                  
Investment, Identifier [Axis]: NEFCO Corp | Capital Goods 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22] 4.8                  
Investment, Identifier [Axis]: NEFCO Corp | Capital Goods 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22] 2.6                  
Investment, Identifier [Axis]: NeoGov Newt Holdco Inc | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[44] 20.0                  
Fair Value, ending balance 19.7 [1],[4],[18],[45]   20.0 [2],[3],[44]              
Investment, Identifier [Axis]: NeoGov Newt Holdco Inc | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 1.1                  
Fair Value, ending balance 3.4 [1],[4],[22]   1.1 [2],[3],[21]              
Investment, Identifier [Axis]: NeoGov Newt Holdco Inc | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 2.4                  
Fair Value, ending balance 4.6 [1],[4],[22]   2.4 [2],[3],[21]              
Investment, Identifier [Axis]: NeoGov Newt Holdco Inc | Software & Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 4.8                  
Fair Value, ending balance [2],[3],[21]     4.8              
Investment, Identifier [Axis]: Net Documents | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 0.8                  
Fair Value, ending balance 75.7 [1],[4],[18],[34],[37],[45]   0.8 [2],[3],[17]              
Investment, Identifier [Axis]: Net Documents | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 32.6                  
Fair Value, ending balance 6.4 [1],[4],[22]   32.6 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Net Documents | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.6                  
Fair Value, ending balance [2],[3],[21]     3.6              
Investment, Identifier [Axis]: Netsmart Technologies Inc | Health Care Equipment & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[39] 60.3                  
Fair Value, ending balance 59.9 [1],[4],[18],[37]   60.3 [2],[3],[17],[39]              
Investment, Identifier [Axis]: Netsmart Technologies Inc | Health Care Equipment & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 6.2                  
Fair Value, ending balance 6.1 [1],[4],[22]   6.2 [2],[3],[21]              
Investment, Identifier [Axis]: Netsmart Technologies Inc | Health Care Equipment & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 6.3                  
Fair Value, ending balance 6.2 [1],[4],[22]   6.3 [2],[3],[21]              
Investment, Identifier [Axis]: New Era Technology Inc | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 10.4                  
Fair Value, ending balance [2],[3],[17]     10.4              
Investment, Identifier [Axis]: New Era Technology Inc | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 2.3                  
Fair Value, ending balance [2],[3],[17]     2.3              
Investment, Identifier [Axis]: New Era Technology Inc | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 2.3                  
Fair Value, ending balance [2],[3],[21]     2.3              
Investment, Identifier [Axis]: New Era Technology Inc, Common Stock | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[19],[26] 0.0                  
Fair Value, ending balance [2],[17],[19],[26]     0.0              
Investment, Identifier [Axis]: New Era Technology Inc, Preferred Stock | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[19],[26] 4.5                  
Fair Value, ending balance [2],[17],[19],[26]     4.5              
Investment, Identifier [Axis]: New Era Technology LLC | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18] 10.7                  
Investment, Identifier [Axis]: New Era Technology LLC | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18] 1.3                  
Investment, Identifier [Axis]: New Era Technology LLC | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22] 3.4                  
Investment, Identifier [Axis]: New Era Technology LLC, Common Stock | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[20],[29] 0.0                  
Investment, Identifier [Axis]: New Era Technology LLC, Preferred Stock | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[20],[29] 2.4                  
Investment, Identifier [Axis]: NewStar Clarendon 2014-1A Class D | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[31] 0.6                  
Fair Value, ending balance 0.6 [1],[4],[18],[36]   0.6 [2],[3],[17],[26],[31]              
Investment, Identifier [Axis]: Newday Group Jersey Ltd, ABF Equity | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[31] 37.4                  
Fair Value, ending balance 7.8 [1],[4],[18],[29],[36]   37.4 [2],[3],[17],[26],[31]              
Investment, Identifier [Axis]: Newday Group Jersey Ltd, Bond | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[36] 31.5                  
Investment, Identifier [Axis]: Nidda Healthcare Holding AG | Pharmaceuticals, Biotechnology & Life Sciences 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31],[42] 1.2                  
Fair Value, ending balance 1.2 [1],[4],[18],[36],[43]   1.2 [2],[3],[17],[31],[42]              
Investment, Identifier [Axis]: Nidda Healthcare Holding AG | Pharmaceuticals, Biotechnology & Life Sciences 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31],[42] 1.2                  
Fair Value, ending balance 1.2 [1],[4],[18],[36],[43]   1.2 [2],[3],[17],[31],[42]              
Investment, Identifier [Axis]: Nidda Healthcare Holding AG | Pharmaceuticals, Biotechnology & Life Sciences 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[36] 28.8                  
Investment, Identifier [Axis]: Nidda Healthcare Holding AG | Pharmaceuticals, Biotechnology & Life Sciences 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22],[36] 6.2                  
Investment, Identifier [Axis]: Nidda Healthcare Holding AG, Common Stock | Pharmaceuticals, Biotechnology & Life Sciences                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[29],[36] 3.2                  
Investment, Identifier [Axis]: Nordic Climate Group Holding AB | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 24.6                  
Fair Value, ending balance 23.8 [1],[4],[18],[36]   24.6 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Nordic Climate Group Holding AB | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 17.9                  
Fair Value, ending balance 17.6 [1],[4],[18],[36]   17.9 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Norway_France, ABF Equity | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 6.8                  
Fair Value, ending balance 5.7 [1],[4],[18],[36]   6.8 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Nottingdale Receivables Limited (FKA TalkTalk Telecom Group Ltd), Revolver | Telecommunication Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 43.1                  
Fair Value, ending balance 40.0 [1],[4],[18],[36]   43.1 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Nottingdale Receivables Limited (FKA TalkTalk Telecom Group Ltd), Revolver | Telecommunication Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 14.9                  
Fair Value, ending balance 17.6 [1],[4],[22],[36]   14.9 [2],[3],[21],[31]              
Investment, Identifier [Axis]: OEConnection LLC | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 23.4                  
Fair Value, ending balance 22.7 [1],[4],[18],[34],[37]   23.4 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: OEConnection LLC | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 0.6                  
Fair Value, ending balance 8.5 [1],[4],[22]   0.6 [2],[3],[21]              
Investment, Identifier [Axis]: OEConnection LLC | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 2.4                  
Fair Value, ending balance 6.9 [1],[4],[22]   2.4 [2],[3],[21]              
Investment, Identifier [Axis]: OEConnection LLC | Software & Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 6.4                  
Fair Value, ending balance [2],[3],[21]     6.4              
Investment, Identifier [Axis]: OEConnection LLC | Software & Services 5                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 6.3                  
Fair Value, ending balance [2],[3],[21]     6.3              
Investment, Identifier [Axis]: One Call Care Management Inc 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 4.7 4.7              
Gross Additions [6]     0.0              
Gross Reductions [8]     (4.8)              
Net Realized Gain (Loss)     0.1              
Net Change in Unrealized Appreciation (Depreciation)     0.0              
Fair Value, ending balance     0.0              
Investment Income [10]     0.4              
PIK Income [10]     0.0              
Fee income [10]     0.0              
Dividend and Other Income [10]     0.0              
Investment, Identifier [Axis]: One Call Care Management Inc 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 28.3 25.1 25.1              
Gross Additions 0.1 [5]   2.4 [6]              
Gross Reductions 0.0 [7]   0.0 [8]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 4.4   0.8              
Fair Value, ending balance 32.8   28.3              
Investment Income 0.0 [9]   (0.1) [10]              
PIK Income 0.7 [9]   2.6 [10]              
Fee income 0.0 [9]   0.0 [10]              
Dividend and Other Income 0.0 [9]   0.0 [10]              
Investment, Identifier [Axis]: One Call Care Management Inc | Health Care Equipment & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25] 28.3                  
Fair Value, ending balance 32.8 [1],[4],[18],[38]   28.3 [2],[3],[17],[25]              
Investment, Identifier [Axis]: One Call Care Management Inc, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.9 1.9 1.9              
Gross Additions 0.0 [5]   0.0 [6]              
Gross Reductions 0.0 [7]   0.0 [8]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   (1.0)              
Fair Value, ending balance 0.9   0.9              
Investment Income 0.0 [9]   0.0 [10]              
PIK Income 0.0 [9]   0.0 [10]              
Fee income 0.0 [9]   0.0 [10]              
Dividend and Other Income 0.0 [9]   0.0 [10]              
Investment, Identifier [Axis]: One Call Care Management Inc, Common Stock | Health Care Equipment & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[25],[26] 0.9                  
Fair Value, ending balance 0.9 [1],[4],[18],[29],[38]   0.9 [2],[17],[25],[26]              
Investment, Identifier [Axis]: One Call Care Management Inc, Preferred Stock A                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 17.5 20.7 20.7              
Gross Additions 0.0 [5]   0.0 [6]              
Gross Reductions 0.0 [7]   0.0 [8]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.8   (3.2)              
Fair Value, ending balance 18.3   17.5              
Investment Income 0.0 [9]   0.0 [10]              
PIK Income 0.0 [9]   0.0 [10]              
Fee income 0.0 [9]   0.0 [10]              
Dividend and Other Income 0.0 [9]   0.0 [10]              
Investment, Identifier [Axis]: One Call Care Management Inc, Preferred Stock A | Health Care Equipment & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[25],[26] 17.5                  
Fair Value, ending balance 18.3 [1],[4],[18],[29],[38]   17.5 [2],[17],[25],[26]              
Investment, Identifier [Axis]: One Call Care Management Inc, Preferred Stock B                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 13.2 12.2 12.2              
Gross Additions 0.0 [5]   0.8 [6]              
Gross Reductions 0.0 [7]   0.0 [8]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (1.9)   0.2              
Fair Value, ending balance 11.3   13.2              
Investment Income 0.0 [9]   0.0 [10]              
PIK Income 0.0 [9]   0.9 [10]              
Fee income 0.0 [9]   0.0 [10]              
Dividend and Other Income 0.0 [9]   0.0 [10]              
Investment, Identifier [Axis]: One Call Care Management Inc, Preferred Stock B | Health Care Equipment & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[25] 13.2                  
Fair Value, ending balance 11.3 [1],[4],[18],[29],[32],[38]   13.2 [2],[17],[25]              
Investment, Identifier [Axis]: Orion Services Group | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 4.0                  
Fair Value, ending balance [2],[3],[21]     4.0              
Investment, Identifier [Axis]: Orion Services Group | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18] 0.8                  
Investment, Identifier [Axis]: Orion Services Group | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22] 3.2                  
Investment, Identifier [Axis]: Oxford Global Resources LLC | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39],[40],[44] 91.9                  
Fair Value, ending balance 100.0 [1],[4],[18],[34],[37],[41],[45]   91.9 [2],[3],[17],[33],[39],[40],[44]              
Investment, Identifier [Axis]: Oxford Global Resources LLC | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 8.4                  
Fair Value, ending balance 7.6 [1],[4],[22]   8.4 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Oxford Global Resources LLC | Commercial & Professional Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 7.6                  
Fair Value, ending balance [2],[3],[21]     7.6              
Investment, Identifier [Axis]: PCI Pharma Services | Health Care Equipment & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31],[33] 41.8                  
Fair Value, ending balance 42.5 [1],[4],[18],[34],[36]   41.8 [2],[3],[17],[31],[33]              
Investment, Identifier [Axis]: PCI Pharma Services | Health Care Equipment & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 0.7                  
Fair Value, ending balance 26.9 [1],[4],[22],[36]   0.7 [2],[3],[17],[31]              
Investment, Identifier [Axis]: PCI Pharma Services | Health Care Equipment & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 26.0                  
Fair Value, ending balance 11.5 [1],[4],[22],[36]   26.0 [2],[3],[21],[31]              
Investment, Identifier [Axis]: PCI Pharma Services | Health Care Equipment & Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 2.0                  
Fair Value, ending balance [2],[3],[21],[31]     2.0              
Investment, Identifier [Axis]: PCI Pharma Services | Health Care Equipment & Services 5                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 11.7                  
Fair Value, ending balance [2],[3],[21],[31]     11.7              
Investment, Identifier [Axis]: PROS Holdings Inc | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[40] 10.9                  
Fair Value, ending balance 10.7 [1],[4],[41]   10.9 [2],[3],[40]              
Investment, Identifier [Axis]: PROS Holdings Inc | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 1.3                  
Fair Value, ending balance 1.2 [1],[4],[22]   1.3 [2],[3],[21]              
Investment, Identifier [Axis]: PSC Group | Transportation 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 1.0                  
Fair Value, ending balance 1.4 [1],[4],[18]   1.0 [2],[3],[17]              
Investment, Identifier [Axis]: PSC Group | Transportation 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 17.6                  
Fair Value, ending balance 19.0 [1],[4],[18],[34],[37]   17.6 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: PSC Group | Transportation 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 1.4                  
Fair Value, ending balance 1.1 [1],[4],[22]   1.4 [2],[3],[21]              
Investment, Identifier [Axis]: PSC Group | Transportation 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 1.6                  
Fair Value, ending balance [2],[3],[21]     1.6              
Investment, Identifier [Axis]: PSKW LLC (dba ConnectiveRx) | Health Care Equipment & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39],[40],[44] 101.3                  
Fair Value, ending balance 101.0 [1],[4],[18],[34],[37],[41],[45]   101.3 [2],[3],[17],[33],[39],[40],[44]              
Investment, Identifier [Axis]: PartsSource Inc | Health Care Equipment & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 3.6                  
Fair Value, ending balance 3.2 [1],[4],[18]   3.6 [2],[3],[17]              
Investment, Identifier [Axis]: PartsSource Inc | Health Care Equipment & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[39] 82.4                  
Fair Value, ending balance 82.2 [1],[4],[18],[37]   82.4 [2],[3],[17],[39]              
Investment, Identifier [Axis]: PartsSource Inc | Health Care Equipment & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 0.7                  
Fair Value, ending balance 1.1 [1],[4],[22]   0.7 [2],[3],[21]              
Investment, Identifier [Axis]: PayPal Danube 2, ABF Equity | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[31] 30.3                  
Fair Value, ending balance 31.4 [1],[4],[18],[36]   30.3 [2],[3],[17],[26],[31]              
Investment, Identifier [Axis]: PayPal Europe Sarl et Cie SCA, ABF Equity | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 70.9                  
Fair Value, ending balance 48.2 [1],[4],[18],[36]   70.9 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Peraton Corp | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[35] 141.8                  
Fair Value, ending balance 121.8 [1],[4],[18]   141.8 [2],[3],[17],[35]              
Investment, Identifier [Axis]: Peraton Corp | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 104.8                  
Fair Value, ending balance 93.4 [1],[4],[18]   104.8 [2],[3],[17]              
Investment, Identifier [Axis]: Philippine Airlines 777, Term Loan | Transportation 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 1.9                  
Fair Value, ending balance 1.8 [1],[4],[18],[36]   1.9 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Philippine Airlines 777, Term Loan | Transportation 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 1.9                  
Fair Value, ending balance 1.8 [1],[4],[18],[36]   1.9 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Philippine Airlines 777, Term Loan | Transportation 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 1.1                  
Fair Value, ending balance 1.1 [1],[4],[22],[36]   1.1 [2],[3],[21],[31]              
Investment, Identifier [Axis]: Philippine Airlines 777, Term Loan | Transportation 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 1.1                  
Fair Value, ending balance 1.1 [1],[4],[22],[36]   1.1 [2],[3],[21],[31]              
Investment, Identifier [Axis]: Pike Corp | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[40],[44] 30.6                  
Fair Value, ending balance 30.1 [1],[4],[41],[45]   30.6 [2],[3],[40],[44]              
Investment, Identifier [Axis]: Pike Corp | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 6.6                  
Fair Value, ending balance 6.5 [1],[4],[22]   6.6 [2],[3],[21]              
Investment, Identifier [Axis]: Pike Corp | Capital Goods 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 4.4                  
Fair Value, ending balance 4.4 [1],[4],[22]   4.4 [2],[3],[21]              
Investment, Identifier [Axis]: Polyconcept North America Inc, Class A - 1 Units | Household & Personal Products                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26] 2.0                  
Fair Value, ending balance 2.0 [1],[4],[18],[29]   2.0 [2],[17],[26]              
Investment, Identifier [Axis]: Powin Energy Corp/NV, Warrants | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[26],[57] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[29],[58]   0.0 [2],[3],[26],[57]              
Investment, Identifier [Axis]: Premise Health Holding Corp | Health Care Equipment & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 5.4                  
Fair Value, ending balance 6.8 [1],[4],[18]   5.4 [2],[3],[17]              
Investment, Identifier [Axis]: Premise Health Holding Corp | Health Care Equipment & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 0.5                  
Fair Value, ending balance 0.4 [1],[4],[18]   0.5 [2],[3],[21]              
Investment, Identifier [Axis]: Premise Health Holding Corp | Health Care Equipment & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 2.3                  
Fair Value, ending balance 0.5 [1],[4],[22]   2.3 [2],[3],[21]              
Investment, Identifier [Axis]: Premise Health Holding Corp | Health Care Equipment & Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22] 0.9                  
Investment, Identifier [Axis]: Prime ST LLC, ABF Equity | Equity Real Estate Investment Trusts (REITs)                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30],[31] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[28],[29]   0.0 [2],[3],[17],[26],[30],[31]              
Investment, Identifier [Axis]: Prime ST LLC, Structured Mezzanine | Equity Real Estate Investment Trusts (REITs)                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 23.7                  
Fair Value, ending balance 22.2 [1],[4],[18],[28],[29],[32]   23.7 [2],[3],[17],[30],[31]              
Investment, Identifier [Axis]: Prime St LLC, ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   (1.1) [14]              
Net Realized Gain (Loss) 0.0   (0.8)              
Net Change in Unrealized Appreciation (Depreciation) 0.0   1.9              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Prime St LLC, Structured Mezzanine                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 23.7 27.6 27.6              
Gross Additions 0.0 [11]   4.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (1.5)   (7.9)              
Fair Value, ending balance 22.2   23.7              
Investment Income 0.9 [15]   3.7 [16]              
PIK Income 0.0 [15]   3.7 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Production Resource Group LLC                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 273.5                  
Gross Additions [11] 17.8                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 0.7                  
Fair Value, ending balance 292.0   273.5              
Investment Income [15] 0.0                  
PIK Income [15] 8.0                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: Production Resource Group LLC 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 195.9 195.9              
Gross Additions [12]     0.0              
Gross Reductions [14]     (192.0)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     (3.9)              
Fair Value, ending balance     0.0              
Investment Income [16]     1.3              
PIK Income [16]     6.9              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Production Resource Group LLC 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.3 0.3              
Gross Additions [12]     0.0              
Gross Reductions [14]     (0.2)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     (0.1)              
Fair Value, ending balance     0.0              
Investment Income [16]     0.0              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Production Resource Group LLC 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 67.7 67.7              
Gross Additions [12]     0.0              
Gross Reductions [14]     (65.7)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     (2.0)              
Fair Value, ending balance     0.0              
Investment Income [16]     1.0              
PIK Income [16]     3.2              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Production Resource Group LLC 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 37.2 37.2              
Gross Additions [12]     0.0              
Gross Reductions [14]     (36.0)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     (1.2)              
Fair Value, ending balance     0.0              
Investment Income [16]     0.5              
PIK Income [16]     1.8              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Production Resource Group LLC 5                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 107.4 107.4              
Gross Additions [12]     0.0              
Gross Reductions [14]     (104.3)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     (3.1)              
Fair Value, ending balance     0.0              
Investment Income [16]     1.6              
PIK Income [16]     5.1              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Production Resource Group LLC 6                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions [12]     0.0              
Gross Reductions [14]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.0              
Fair Value, ending balance     0.0              
Investment Income [16]     0.1              
PIK Income [16]     0.3              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Production Resource Group LLC 7                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions [12]     0.0              
Gross Reductions [14]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.0              
Fair Value, ending balance     0.0              
Investment Income [16]     0.2              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Production Resource Group LLC 8                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 273.5 0.0 0.0              
Gross Additions [12]     263.9              
Gross Reductions [14]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     9.6              
Fair Value, ending balance     273.5              
Investment Income [16]     0.1              
PIK Income [16]     7.1              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Production Resource Group LLC | Media & Entertainment                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30] 273.5                  
Fair Value, ending balance 292.0 [1],[4],[18],[28]   273.5 [2],[3],[17],[30]              
Investment, Identifier [Axis]: Production Resource Group LLC, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 95.3 0.0 0.0              
Gross Additions 0.0 [11]   95.3 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (60.0)   0.0              
Fair Value, ending balance 35.3   95.3              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Production Resource Group LLC, Common Stock | Media & Entertainment                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26],[30] 95.3                  
Fair Value, ending balance 35.3 [1],[4],[18],[28],[29]   95.3 [2],[17],[26],[30]              
Investment, Identifier [Axis]: Production Resource Group LLC, Preferred Stock, Series A PIK                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 67.2 67.2              
Gross Additions [12]     0.0              
Gross Reductions [14]     0.0              
Net Realized Gain (Loss)     (18.1)              
Net Change in Unrealized Appreciation (Depreciation)     (49.1)              
Fair Value, ending balance     0.0              
Investment Income [16]     0.0              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Production Resource Group LLC, Preferred Stock, Series B PIK                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions [12]     0.0              
Gross Reductions [14]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.0              
Fair Value, ending balance     0.0              
Investment Income [16]     0.0              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Proserv Acquisition LLC, Class A Preferred Units                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 2.2 2.2 2.2              
Gross Additions 0.0 [5]   0.0 [6]              
Gross Reductions 0.0 [7]   0.0 [8]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 2.2   2.2              
Investment Income 0.0 [9]   0.0 [10]              
PIK Income 0.0 [9]   0.0 [10]              
Fee income 0.0 [9]   0.0 [10]              
Dividend and Other Income 0.0 [9]   0.0 [10]              
Investment, Identifier [Axis]: Proserv Acquisition LLC, Class A Preferred Units | Energy                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[25],[26],[31] 2.2                  
Fair Value, ending balance 2.2 [1],[4],[18],[29],[36],[38]   2.2 [2],[17],[25],[26],[31]              
Investment, Identifier [Axis]: Quoizel, LLC 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 6.8 7.1 7.1              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (0.3)   (0.3)              
Fair Value, ending balance 6.5   6.8              
Investment Income 0.2 [15]   0.8 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Quoizel, LLC 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 7.1 7.4 7.4              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (0.3)   (0.3)              
Fair Value, ending balance 6.8   7.1              
Investment Income 0.2 [15]   0.8 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Quoizel, LLC | Consumer Durables & Apparel 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30] 6.8                  
Fair Value, ending balance 6.5 [1],[4],[18],[28]   6.8 [2],[3],[17],[30]              
Investment, Identifier [Axis]: Quoizel, LLC | Consumer Durables & Apparel 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30] 7.1                  
Fair Value, ending balance 6.8 [1],[4],[18],[28]   7.1 [2],[3],[17],[30]              
Investment, Identifier [Axis]: Quoizel, LLC, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 2.7 6.1 6.1              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (0.8)   (3.4)              
Fair Value, ending balance 1.9   2.7              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Quoizel, LLC, Common Stock | Consumer Durables & Apparel                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26],[30] 2.7                  
Fair Value, ending balance 1.9 [1],[4],[18],[28],[29]   2.7 [2],[17],[26],[30]              
Investment, Identifier [Axis]: Quorum Health Corp, Private Equity 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 10.0 10.1 10.1              
Gross Additions 0.0 [11]   0.9 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.1   (1.0)              
Fair Value, ending balance 10.1   10.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Quorum Health Corp, Private Equity 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 7.4 0.0 0.0              
Gross Additions 0.0 [11]   2.1 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.1   5.3              
Fair Value, ending balance 7.5   7.4              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Quorum Health Corp, Private Equity | Health Care Equipment & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26],[30] 10.0                  
Fair Value, ending balance 10.1 [1],[4],[18],[28],[29]   10.0 [2],[17],[26],[30]              
Investment, Identifier [Axis]: Quorum Health Corp, Private Equity | Health Care Equipment & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26],[30] 7.4                  
Fair Value, ending balance 7.5 [1],[4],[18],[28],[29]   7.4 [2],[17],[26],[30]              
Investment, Identifier [Axis]: Quorum Health Corp, Trade Claim                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.5 0.9 0.9              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   (0.4)              
Fair Value, ending balance 0.5   0.5              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Quorum Health Corp, Trade Claim | Health Care Equipment & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26],[30] 0.5                  
Fair Value, ending balance 0.5 [1],[4],[18],[28],[29]   0.5 [2],[17],[26],[30]              
Investment, Identifier [Axis]: Quorum Health Corp, Trust Initial Funding Units                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.1 0.1 0.1              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 0.1   0.1              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Quorum Health Corp, Trust Initial Funding Units | Health Care Equipment & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26],[30] 0.1                  
Fair Value, ending balance 0.1 [1],[4],[18],[28],[29]   0.1 [2],[17],[26],[30]              
Investment, Identifier [Axis]: Radwell International LLC | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[19],[33],[44] 126.7                  
Fair Value, ending balance 124.5 [1],[4],[18],[20],[34],[45]   126.7 [2],[3],[17],[19],[33],[44]              
Investment, Identifier [Axis]: Radwell International LLC | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 1.2                  
Fair Value, ending balance 1.6 [1],[4],[18]   1.2 [2],[3],[17]              
Investment, Identifier [Axis]: Radwell International LLC | Capital Goods 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 5.8                  
Fair Value, ending balance 5.3 [1],[4],[22]   5.8 [2],[3],[21]              
Investment, Identifier [Axis]: Railpros Inc | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33] 2.6                  
Fair Value, ending balance 2.8 [1],[4],[18],[34]   2.6 [2],[3],[17],[33]              
Investment, Identifier [Axis]: Railpros Inc | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 0.8                  
Fair Value, ending balance 0.6 [1],[4],[22]   0.8 [2],[3],[21]              
Investment, Identifier [Axis]: Railpros Inc | Commercial & Professional Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 0.4                  
Fair Value, ending balance 0.4 [1],[4],[22]   0.4 [2],[3],[21]              
Investment, Identifier [Axis]: Reliant Rehab Hospital Cincinnati LLC | Health Care Equipment & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[35] 43.3                  
Fair Value, ending balance 42.8 [1],[4],[18]   43.3 [2],[3],[17],[35]              
Investment, Identifier [Axis]: Reliant Rehab Hospital Cincinnati LLC | Health Care Equipment & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[27],[35] 11.1                  
Fair Value, ending balance 10.7 [1],[4],[18],[29],[32]   11.1 [2],[3],[17],[26],[27],[35]              
Investment, Identifier [Axis]: Resa Power LLC | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[40] 67.6                  
Fair Value, ending balance 70.2 [1],[4],[18],[34],[41]   67.6 [2],[3],[17],[33],[40]              
Investment, Identifier [Axis]: Resa Power LLC | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 12.3                  
Fair Value, ending balance 8.6 [1],[4],[22]   12.3 [2],[3],[21]              
Investment, Identifier [Axis]: Resa Power LLC | Commercial & Professional Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 8.6                  
Fair Value, ending balance 9.9 [1],[4],[22]   8.6 [2],[3],[21]              
Investment, Identifier [Axis]: Residential Opportunities I LLC, ABF Equity | Real Estate Management & Development                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26] 0.1                  
Fair Value, ending balance 0.1 [1],[4],[18],[29]   0.1 [2],[3],[17],[26]              
Investment, Identifier [Axis]: Revere Superior Holdings Inc | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[39] 42.2                  
Fair Value, ending balance 41.8 [1],[4],[18],[37]   42.2 [2],[3],[17],[39]              
Investment, Identifier [Axis]: Revere Superior Holdings Inc | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 0.5                  
Fair Value, ending balance 0.5 [1],[4],[18]   0.5 [2],[3],[17]              
Investment, Identifier [Axis]: Revere Superior Holdings Inc | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.3                  
Fair Value, ending balance 3.3 [1],[4],[22]   3.3 [2],[3],[21]              
Investment, Identifier [Axis]: Rialto Capital Management LLC | Financial Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 20.3                  
Fair Value, ending balance 20.3 [1],[4],[18],[34],[37]   20.3 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Rialto Capital Management LLC | Financial Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 1.0                  
Fair Value, ending balance 1.0 [1],[4],[22]   1.0 [2],[3],[21]              
Investment, Identifier [Axis]: Rockefeller Capital Management LP | Financial Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 24.5                  
Fair Value, ending balance 24.5 [1],[4],[18],[34],[37]   24.5 [2],[3],[17]              
Investment, Identifier [Axis]: Rockefeller Capital Management LP | Financial Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 8.7                  
Fair Value, ending balance 8.7 [1],[4],[22]   8.7 [2],[3],[21]              
Investment, Identifier [Axis]: Roemanu LLC (FKA Toorak Capital Partners LLC), ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 197.2 238.9 238.9              
Gross Additions [12]     0.0              
Gross Reductions [14]     (13.6)              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     (28.1)              
Fair Value, ending balance     197.2              
Investment Income [16]     0.0              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     9.4              
Investment, Identifier [Axis]: Roemanu LLC, ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 197.2                  
Gross Additions [11] 0.0                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 0.1                  
Fair Value, ending balance 197.3   197.2              
Investment Income [15] 0.0                  
PIK Income [15] 0.0                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: Roemanu LLC, ABF Equity | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30] 197.2                  
Fair Value, ending balance 197.3 [1],[4],[18],[28]   197.2 [2],[3],[17],[30]              
Investment, Identifier [Axis]: SAMBA Safety Inc | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 4.7                  
Fair Value, ending balance 4.6 [1],[4],[18],[37]   4.7 [2],[3],[17]              
Investment, Identifier [Axis]: SAMBA Safety Inc | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18]   0.0 [2],[3],[17]              
Investment, Identifier [Axis]: SAMBA Safety Inc | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 0.6                  
Fair Value, ending balance 0.9 [1],[4],[22]   0.6 [2],[3],[21]              
Investment, Identifier [Axis]: SAMBA Safety Inc | Software & Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 0.9                  
Fair Value, ending balance 0.6 [1],[4],[22]   0.9 [2],[3],[21]              
Investment, Identifier [Axis]: SCRIPPS SPV LLC (FKA EW Scripps Co/The), Revolver | Media & Entertainment 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 10.1                  
Fair Value, ending balance 8.8 [1],[4],[18],[36]   10.1 [2],[3],[17],[31]              
Investment, Identifier [Axis]: SCRIPPS SPV LLC (FKA EW Scripps Co/The), Revolver | Media & Entertainment 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 5.3                  
Fair Value, ending balance 6.5 [1],[4],[22],[36]   5.3 [2],[3],[21],[31]              
Investment, Identifier [Axis]: SKP German Bank, ABF Equity | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[31] 5.4                  
Fair Value, ending balance 4.5 [1],[4],[18],[36]   5.4 [2],[3],[17],[26],[31]              
Investment, Identifier [Axis]: STV Group Inc | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17],[33] 9.8                  
Fair Value, ending balance 9.8 [1],[4],[18],[34]   9.8 [3],[17],[33]              
Investment, Identifier [Axis]: STV Group Inc | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[21] 8.3                  
Fair Value, ending balance 8.3 [1],[4],[22]   8.3 [3],[21]              
Investment, Identifier [Axis]: STV Group Inc | Capital Goods 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[21] 11.9                  
Fair Value, ending balance 11.9 [1],[4],[22]   11.9 [3],[21]              
Investment, Identifier [Axis]: Safe-Guard Products International LLC | Financial Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39],[40] 40.7                  
Fair Value, ending balance 39.4 [1],[4],[18],[34],[37],[41]   40.7 [2],[3],[17],[33],[39],[40]              
Investment, Identifier [Axis]: Safe-Guard Products International LLC | Financial Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 8.8                  
Fair Value, ending balance 8.8 [1],[4],[22]   8.8 [2],[3],[21]              
Investment, Identifier [Axis]: Sallie Mae Levered, ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 1.1 0.0 0.0              
Gross Additions 1.4 [11]   1.1 [12]              
Gross Reductions (0.4) [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.1   0.0              
Fair Value, ending balance 2.2   1.1              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Sallie Mae Levered, ABF Equity | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30],[31] 1.1                  
Fair Value, ending balance 2.2 [1],[4],[18],[28],[29],[36]   1.1 [2],[3],[17],[26],[30],[31]              
Investment, Identifier [Axis]: Sallie Mae Levered, Bond                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 4.3 0.0 0.0              
Gross Additions [12]     4.3              
Gross Reductions [14]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.0              
Fair Value, ending balance     4.3              
Investment Income [16]     0.0              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Sallie Mae Levered, Bond 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 4.3                  
Gross Additions [11] 0.0                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 0.0                  
Fair Value, ending balance 4.3   4.3              
Investment Income [15] 0.1                  
PIK Income [15] 0.0                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: Sallie Mae Levered, Bond 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0                  
Gross Additions [11] 4.3                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 0.0                  
Fair Value, ending balance 4.3   0.0              
Investment Income [15] 0.1                  
PIK Income [15] 0.0                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: Sallie Mae Levered, Bond 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0                  
Gross Additions [11] 1.2                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 0.0                  
Fair Value, ending balance 1.2   0.0              
Investment Income [15] 0.0                  
PIK Income [15] 0.0                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: Sallie Mae Levered, Bond 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0                  
Gross Additions [11] 0.6                  
Gross Reductions [13] 0.0                  
Net Realized Gain (Loss) 0.0                  
Net Change in Unrealized Appreciation (Depreciation) 0.0                  
Fair Value, ending balance 0.6   0.0              
Investment Income [15] 0.0                  
PIK Income [15] 0.0                  
Fee income [15] 0.0                  
Dividend and Other Income [15] 0.0                  
Investment, Identifier [Axis]: Sallie Mae Levered, Bond | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 4.3                  
Fair Value, ending balance [2],[3],[17],[30],[31]     4.3              
Investment, Identifier [Axis]: Sallie Mae Levered, Bond | Financial Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[36] 4.3                  
Investment, Identifier [Axis]: Sallie Mae Levered, Bond | Financial Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[36] 4.3                  
Investment, Identifier [Axis]: Sallie Mae Levered, Bond | Financial Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[36] 1.2                  
Investment, Identifier [Axis]: Sallie Mae Levered, Bond | Financial Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[28],[36] 0.6                  
Investment, Identifier [Axis]: Sallie Mae Levered, Term Loan                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.1 0.0 0.0              
Gross Additions 0.2 [11]   0.1 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.0              
Fair Value, ending balance 0.3   0.1              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Sallie Mae Levered, Term Loan | Financial Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 0.1                  
Fair Value, ending balance 0.3 [1],[4],[18],[28],[36]   0.1 [2],[3],[17],[30],[31]              
Investment, Identifier [Axis]: Sallie Mae Levered, Term Loan | Financial Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[30],[31] 0.3                  
Fair Value, ending balance 0.1 [1],[4],[22],[28],[36]   0.3 [2],[3],[21],[30],[31]              
Investment, Identifier [Axis]: Service Express Inc | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 33.0                  
Fair Value, ending balance 61.7 [1],[4],[18]   33.0 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Service Express Inc | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 61.9                  
Fair Value, ending balance 32.5 [1],[4],[18],[34],[37]   61.9 [2],[3],[17]              
Investment, Identifier [Axis]: Service Express Inc | Commercial & Professional Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 1.2                  
Fair Value, ending balance 10.6 [1],[4],[22]   1.2 [2],[3],[17]              
Investment, Identifier [Axis]: Service Express Inc | Commercial & Professional Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 0.1                  
Fair Value, ending balance 13.4 [1],[4],[22]   0.1 [2],[3],[17]              
Investment, Identifier [Axis]: Service Express Inc | Commercial & Professional Services 5                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 10.7                  
Fair Value, ending balance [2],[3],[21]     10.7              
Investment, Identifier [Axis]: Service Express Inc | Commercial & Professional Services 6                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 12.3                  
Fair Value, ending balance [2],[3],[21]     12.3              
Investment, Identifier [Axis]: Service Logic LLC | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 28.8                  
Fair Value, ending balance 28.7 [1],[4],[18]   28.8 [2],[3],[17]              
Investment, Identifier [Axis]: Service Logic LLC | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 7.9                  
Fair Value, ending balance 1.2 [1],[4],[18]   7.9 [2],[3],[21]              
Investment, Identifier [Axis]: Service Logic LLC | Commercial & Professional Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 4.0                  
Fair Value, ending balance 7.9 [1],[4],[22]   4.0 [2],[3],[21]              
Investment, Identifier [Axis]: Service Logic LLC | Commercial & Professional Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22] 2.8                  
Investment, Identifier [Axis]: Shaw Development LLC | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 27.9                  
Fair Value, ending balance 27.9 [1],[4],[18]   27.9 [2],[3],[17]              
Investment, Identifier [Axis]: Slate Venture Holdings LP, ABF Equity | Consumer Durables & Apparel                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 20.6                  
Fair Value, ending balance 22.4 [1],[4],[18],[29]   20.6 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Slate Venture Holdings LP, Term Loan | Consumer Durables & Apparel                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 14.8                  
Fair Value, ending balance 13.1 [1],[4],[18]   14.8 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Solera LLC | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 260.8                  
Fair Value, ending balance 217.6 [1],[4],[18]   260.8 [2],[3],[17]              
Investment, Identifier [Axis]: Sorenson Communications LLC , Telecommunication Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[50],[55] 13.3                  
Fair Value, ending balance [2],[3],[17],[26],[50],[55]     13.3              
Investment, Identifier [Axis]: Sorenson Communications LLC | Telecommunication Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[18],[29],[51],[56] 13.2                  
Investment, Identifier [Axis]: Sorenson Communications LLC | Telecommunication Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[50],[55] 47.0                  
Fair Value, ending balance 47.5 [1],[4],[18],[29],[51],[56]   47.0 [2],[3],[17],[26],[50],[55]              
Investment, Identifier [Axis]: Sorenson Communications LLC, Common Stock | Telecommunication Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26],[50],[55] 5.4                  
Fair Value, ending balance 3.1 [1],[4],[18],[29],[51],[56]   5.4 [2],[17],[26],[50],[55]              
Investment, Identifier [Axis]: Sotheby's, Revolver | Consumer Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22] 7.8                  
Investment, Identifier [Axis]: Source Code LLC | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[39],[40],[44] 52.5                  
Fair Value, ending balance 51.5 [1],[4],[18],[37],[41],[45]   52.5 [2],[3],[17],[39],[40],[44]              
Investment, Identifier [Axis]: Sphera Solutions Inc | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[33] 7.7                  
Fair Value, ending balance 7.3 [1],[4],[18],[34]   7.7 [2],[3],[33]              
Investment, Identifier [Axis]: Sphera Solutions Inc | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 0.8                  
Fair Value, ending balance 0.9 [1],[4],[18]   0.8 [2],[3],[17]              
Investment, Identifier [Axis]: Sphera Solutions Inc | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 6.4                  
Fair Value, ending balance 6.1 [1],[4],[22]   6.4 [2],[3],[21]              
Investment, Identifier [Axis]: Sphera Solutions Inc | Software & Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 3.4                  
Fair Value, ending balance 3.1 [1],[4],[22]   3.4 [2],[3],[21]              
Investment, Identifier [Axis]: Sphera Solutions Inc | Software & Services 5                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 20.0                  
Fair Value, ending balance 19.0 [1],[4],[22]   20.0 [2],[3],[21]              
Investment, Identifier [Axis]: Spins LLC | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17],[33],[40] 32.4                  
Fair Value, ending balance 32.1 [1],[4],[18],[34],[41]   32.4 [3],[17],[33],[40]              
Investment, Identifier [Axis]: Spins LLC | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[21] 3.2                  
Fair Value, ending balance 7.6 [1],[4],[18],[37]   3.2 [3],[21]              
Investment, Identifier [Axis]: Spins LLC | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22] 3.1                  
Investment, Identifier [Axis]: Spotless Brands LLC | Consumer Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17],[33],[39] 30.8                  
Fair Value, ending balance 30.5 [1],[4],[18],[34],[37]   30.8 [3],[17],[33],[39]              
Investment, Identifier [Axis]: Spotless Brands LLC | Consumer Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17] 35.8                  
Fair Value, ending balance 35.5 [1],[4],[18]   35.8 [3],[17]              
Investment, Identifier [Axis]: Spotless Brands LLC | Consumer Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17] 0.9                  
Fair Value, ending balance 1.2 [1],[4],[18]   0.9 [3],[17]              
Investment, Identifier [Axis]: Spotless Brands LLC | Consumer Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[21] 5.3                  
Fair Value, ending balance 5.0 [1],[4],[22]   5.3 [3],[21]              
Investment, Identifier [Axis]: Star Mountain Diversified Credit Income Fund III, LP, ABF Equity | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[31],[54] 25.1                  
Fair Value, ending balance 23.1 [1],[4],[29],[36],[59]   25.1 [2],[3],[31],[54]              
Investment, Identifier [Axis]: Stuart Weitzman Inc, Common Stock | Consumer Durables & Apparel                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[17],[26] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[29]   0.0 [2],[17],[26]              
Investment, Identifier [Axis]: Styron Receivables Funding Designated Activity Company (FKA Trinseo Materials), Revolver | Materials 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 55.8                  
Fair Value, ending balance 66.2 [1],[4],[18],[36]   55.8 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Styron Receivables Funding Designated Activity Company (FKA Trinseo Materials), Revolver | Materials 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 15.1                  
Fair Value, ending balance 4.7 [1],[4],[22],[36]   15.1 [2],[3],[21],[31]              
Investment, Identifier [Axis]: Summit Interconnect Inc | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17],[40] 123.1                  
Fair Value, ending balance 123.2 [1],[4],[18],[41]   123.1 [3],[17],[40]              
Investment, Identifier [Axis]: SunPower Financial, ABF Equity | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 2.9                  
Fair Value, ending balance 2.8 [1],[4],[18],[36]   2.9 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Sweeping Corp of America LLC | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17] 1.1                  
Fair Value, ending balance 1.1 [1],[4],[18]   1.1 [3],[17]              
Investment, Identifier [Axis]: Sweeping Corp of America LLC | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17] 15.5                  
Fair Value, ending balance 15.4 [1],[4],[18]   15.5 [3],[17]              
Investment, Identifier [Axis]: Sweeping Corp of America LLC | Commercial & Professional Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17] 33.1                  
Fair Value, ending balance 33.8 [1],[4],[18]   33.1 [3],[17]              
Investment, Identifier [Axis]: Sweeping Corp of America LLC | Commercial & Professional Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[21] 4.5                  
Fair Value, ending balance 4.5 [1],[4],[22]   4.5 [3],[21]              
Investment, Identifier [Axis]: Sweeping Corp of America LLC | Commercial & Professional Services 5                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26] 5.2                  
Fair Value, ending balance 5.4 [1],[4],[18],[29]   5.2 [2],[3],[17],[26]              
Investment, Identifier [Axis]: Sweeping Corp of America LLC | Commercial & Professional Services 6                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[29]   0.0 [2],[3],[17],[26]              
Investment, Identifier [Axis]: TDC LLP, ABF Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 1.9 1.9              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   (2.0) [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 0.0   0.1              
Fair Value, ending balance 0.0   0.0              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: TDC LLP, ABF Equity | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30],[31] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[28],[29],[36]   0.0 [2],[3],[17],[26],[30],[31]              
Investment, Identifier [Axis]: TDC LLP, Preferred Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 12.5 36.8 36.8              
Gross Additions 3.6 [11]   15.9 [12]              
Gross Reductions 0.0 [13]   (41.9) [14]              
Net Realized Gain (Loss) 0.0   1.0              
Net Change in Unrealized Appreciation (Depreciation) (0.4)   0.7              
Fair Value, ending balance 15.7   12.5              
Investment Income 0.4 [15]   1.5 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: TDC LLP, Preferred Equity | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 12.5                  
Fair Value, ending balance 15.7 [1],[4],[18],[28],[36]   12.5 [2],[3],[17],[30],[31]              
Investment, Identifier [Axis]: TPSI Receivables LLC (Tropicana Products Inc), Revolver | Food, Beverage & Tobacco 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 40.1                  
Fair Value, ending balance 40.1 [1],[4],[18],[36]   40.1 [2],[3],[17],[31]              
Investment, Identifier [Axis]: TPSI Receivables LLC (Tropicana Products Inc), Revolver | Food, Beverage & Tobacco 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 6.0                  
Fair Value, ending balance 6.0 [1],[4],[22],[36]   6.0 [2],[3],[21],[31]              
Investment, Identifier [Axis]: Tangoe LLC | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17],[35] 151.4                  
Fair Value, ending balance 136.0 [1],[4],[18]   151.4 [3],[17],[35]              
Investment, Identifier [Axis]: Tangoe LLC | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17],[26],[27],[35] 0.0                  
Fair Value, ending balance 0.0 [1],[4],[18],[29],[32]   0.0 [3],[17],[26],[27],[35]              
Investment, Identifier [Axis]: Time Manufacturing Co | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17] 36.9                  
Fair Value, ending balance 37.7 [1],[4],[18]   36.9 [3],[17]              
Investment, Identifier [Axis]: Time Manufacturing Co | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17] 6.9                  
Fair Value, ending balance 8.1 [1],[4],[18]   6.9 [3],[17]              
Investment, Identifier [Axis]: Time Manufacturing Co | Capital Goods 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17] 13.1                  
Fair Value, ending balance 13.1 [1],[4],[18]   13.1 [3],[17]              
Investment, Identifier [Axis]: Time Manufacturing Co | Capital Goods 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[21] 1.0                  
Fair Value, ending balance 0.0 [1],[4],[22]   1.0 [3],[21]              
Investment, Identifier [Axis]: Time Manufacturing Co | Capital Goods 5                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[21] 11.3                  
Fair Value, ending balance 11.6 [1],[4],[22]   11.3 [3],[21]              
Investment, Identifier [Axis]: Trackunit ApS | Software & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[21],[31] 32.9                  
Fair Value, ending balance [3],[21],[31]     32.9              
Investment, Identifier [Axis]: Trackunit ApS | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22],[36] 10.7                  
Investment, Identifier [Axis]: Trackunit ApS | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22],[36] 21.3                  
Investment, Identifier [Axis]: Turnpoint Services Inc | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17] 0.6                  
Fair Value, ending balance 0.6 [1],[4],[18]   0.6 [3],[17]              
Investment, Identifier [Axis]: Turnpoint Services Inc | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[39] 8.3                  
Fair Value, ending balance 8.2 [1],[4],[37]   8.3 [3],[39]              
Investment, Identifier [Axis]: Turnpoint Services Inc | Capital Goods 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[21] 0.9                  
Fair Value, ending balance 0.9 [1],[4],[22]   0.9 [3],[21]              
Investment, Identifier [Axis]: Turnpoint Services Inc | Capital Goods 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[21] 2.5                  
Fair Value, ending balance 2.5 [1],[4],[22]   2.5 [3],[21]              
Investment, Identifier [Axis]: USIC Holdings Inc | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17],[33],[39],[40],[44] 124.5                  
Fair Value, ending balance 61.4 [1],[4],[18],[34],[37],[41],[45]   124.5 [3],[17],[33],[39],[40],[44]              
Investment, Identifier [Axis]: USIC Holdings Inc | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17] 7.1                  
Fair Value, ending balance 8.6 [1],[4],[18]   7.1 [3],[17]              
Investment, Identifier [Axis]: USIC Holdings Inc | Commercial & Professional Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[21] 3.1                  
Fair Value, ending balance 1.1 [1],[4],[22]   3.1 [3],[21]              
Investment, Identifier [Axis]: USIC Holdings Inc | Commercial & Professional Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[21] 8.1                  
Fair Value, ending balance 1.3 [1],[4],[22]   8.1 [3],[21]              
Investment, Identifier [Axis]: Ultra Electronics Holdings Ltd | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17],[31],[42] 1.7                  
Fair Value, ending balance 1.3 [1],[4],[18],[36],[43]   1.7 [3],[17],[31],[42]              
Investment, Identifier [Axis]: Ultra Electronics Holdings Ltd | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 19.0                  
Fair Value, ending balance [2],[3],[17],[31]     19.0              
Investment, Identifier [Axis]: Ultra Electronics Holdings Ltd | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 32.5                  
Fair Value, ending balance [2],[3],[17],[31]     32.5              
Investment, Identifier [Axis]: Ultra Electronics Holdings PLC, Private Equity | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[31] 7.7                  
Fair Value, ending balance 4.4 [1],[4],[18],[29],[36]   7.7 [2],[3],[17],[26],[31]              
Investment, Identifier [Axis]: Ultra Electronics Holdings PLC, Private Equity | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[31] 2.5                  
Fair Value, ending balance 8.3 [1],[4],[18],[29],[36]   2.5 [2],[3],[17],[26],[31]              
Investment, Identifier [Axis]: Valeo Foods Group Ltd | Food, Beverage & Tobacco                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 4.4                  
Fair Value, ending balance 4.3 [1],[4],[18],[36]   4.4 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Vehicle Secured Funding Trust, ABF Equity | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 14.3                  
Fair Value, ending balance 11.0 [1],[4],[18],[36]   14.3 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Vehicle Secured Funding Trust, Term Loan | Financial Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 31.7                  
Fair Value, ending balance 31.4 [1],[4],[18],[36]   31.7 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Veriforce LLC | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17],[31] 2.6                  
Fair Value, ending balance 2.6 [1],[4],[18],[36]   2.6 [3],[17],[31]              
Investment, Identifier [Axis]: Veriforce LLC | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[21],[31] 2.1                  
Fair Value, ending balance 2.0 [1],[4],[22],[36]   2.1 [3],[21],[31]              
Investment, Identifier [Axis]: Veriforce LLC | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[21],[31] 3.7                  
Fair Value, ending balance 3.7 [1],[4],[22],[36]   3.7 [3],[21],[31]              
Investment, Identifier [Axis]: Vermont Information Processing Inc | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17],[39] 8.4                  
Fair Value, ending balance 8.1 [1],[4],[18],[37]   8.4 [3],[17],[39]              
Investment, Identifier [Axis]: Vermont Information Processing Inc | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[21] 9.6                  
Fair Value, ending balance 9.4 [1],[4],[22]   9.6 [3],[21]              
Investment, Identifier [Axis]: Vermont Information Processing Inc | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[21] 2.9                  
Fair Value, ending balance 2.8 [1],[4],[22]   2.9 [3],[21]              
Investment, Identifier [Axis]: Version1 Software Ltd | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17],[31] 2.3                  
Fair Value, ending balance 2.3 [1],[4],[18],[36]   2.3 [3],[17],[31]              
Investment, Identifier [Axis]: Version1 Software Ltd | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[21],[31] 13.2                  
Fair Value, ending balance 13.2 [1],[4],[22],[36]   13.2 [3],[21],[31]              
Investment, Identifier [Axis]: VetCor Professional Practices LLC | Health Care Equipment & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [3],[17],[33],[39] 67.2                  
Fair Value, ending balance 65.3 [1],[4],[18],[34],[37]   67.2 [3],[17],[33],[39]              
Investment, Identifier [Axis]: VetCor Professional Practices LLC | Health Care Equipment & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 0.8                  
Fair Value, ending balance 2.5 [1],[4],[18]   0.8 [2],[3],[17]              
Investment, Identifier [Axis]: VetCor Professional Practices LLC | Health Care Equipment & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 8.3                  
Fair Value, ending balance 8.1 [1],[4],[18],[34],[37]   8.3 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: VetCor Professional Practices LLC | Health Care Equipment & Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 13.4                  
Fair Value, ending balance 13.0 [1],[4],[18]   13.4 [2],[3],[17]              
Investment, Identifier [Axis]: VetCor Professional Practices LLC | Health Care Equipment & Services 5                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 5.9                  
Fair Value, ending balance 4.1 [1],[4],[22]   5.9 [2],[3],[21]              
Investment, Identifier [Axis]: VetCor Professional Practices LLC | Health Care Equipment & Services 6                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 20.8                  
Fair Value, ending balance 20.1 [1],[4],[22]   20.8 [2],[3],[21]              
Investment, Identifier [Axis]: Vitu | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[40] 27.6                  
Fair Value, ending balance 27.5 [1],[4],[18],[34],[41]   27.6 [2],[3],[17],[33],[40]              
Investment, Identifier [Axis]: Vitu | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 9.1                  
Fair Value, ending balance 9.1 [1],[4],[22]   9.1 [2],[3],[21]              
Investment, Identifier [Axis]: Vytalogy Wellness LLC (fka Jarrow Formulas Inc) | Household & Personal Products                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[19],[40] 103.7                  
Fair Value, ending balance 102.1 [1],[4],[18],[20],[41]   103.7 [2],[3],[17],[19],[40]              
Investment, Identifier [Axis]: Waste Services Group Pty Ltd | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 2.6                  
Fair Value, ending balance 2.6 [1],[4],[18],[36]   2.6 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Waste Services Group Pty Ltd | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 4.8                  
Fair Value, ending balance 4.8 [1],[4],[22],[36]   4.8 [2],[3],[21],[31]              
Investment, Identifier [Axis]: Wealth Enhancement Group LLC | Financial Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 0.0                  
Fair Value, ending balance 14.3 [1],[4],[18],[34]   0.0 [2],[3],[17]              
Investment, Identifier [Axis]: Wealth Enhancement Group LLC | Financial Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33] 9.5                  
Fair Value, ending balance 2.8 [1],[4],[22]   9.5 [2],[3],[17],[33]              
Investment, Identifier [Axis]: Wealth Enhancement Group LLC | Financial Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 2.8                  
Fair Value, ending balance 7.0 [1],[4],[22]   2.8 [2],[3],[21]              
Investment, Identifier [Axis]: Wealth Enhancement Group LLC | Financial Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 13.9                  
Fair Value, ending balance 2.1 [1],[4],[22]   13.9 [2],[3],[21]              
Investment, Identifier [Axis]: Wedgewood Weddings | Consumer Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[33] 7.7                  
Fair Value, ending balance 7.7 [1],[4],[34]   7.7 [2],[3],[33]              
Investment, Identifier [Axis]: Wedgewood Weddings | Consumer Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 5.8                  
Fair Value, ending balance 5.8 [1],[4],[22]   5.8 [2],[3],[21]              
Investment, Identifier [Axis]: Wedgewood Weddings | Consumer Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 5.8                  
Fair Value, ending balance 5.8 [1],[4],[22]   5.8 [2],[3],[21]              
Investment, Identifier [Axis]: West Star Aviation Inc | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33] 28.4                  
Fair Value, ending balance 20.0 [1],[4],[18],[34]   28.4 [2],[3],[17],[33]              
Investment, Identifier [Axis]: West Star Aviation Inc | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 1.8                  
Fair Value, ending balance 1.2 [1],[4],[18]   1.8 [2],[3],[17]              
Investment, Identifier [Axis]: West Star Aviation Inc | Capital Goods 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 9.6                  
Fair Value, ending balance 13.7 [1],[4],[18]   9.6 [2],[3],[21]              
Investment, Identifier [Axis]: West Star Aviation Inc | Capital Goods 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 30.1                  
Fair Value, ending balance 30.7 [1],[4],[22]   30.1 [2],[3],[21]              
Investment, Identifier [Axis]: West Star Aviation Inc | Capital Goods 5                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, ending balance [1],[4],[22] 4.2                  
Investment, Identifier [Axis]: Wittur Holding GmbH 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 65.2 54.1 54.1              
Gross Additions 2.0 [11]   3.8 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (1.3)   7.3              
Fair Value, ending balance 65.9   65.2              
Investment Income 0.2 [15]   0.7 [16]              
PIK Income 0.8 [15]   3.1 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Wittur Holding GmbH 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 13.3 0.0 0.0              
Gross Additions 0.8 [11]   6.3 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) (0.7)   7.0              
Fair Value, ending balance 13.4   13.3              
Investment Income 0.4 [15]   1.0 [16]              
PIK Income 0.2 [15]   0.4 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Wittur Holding GmbH | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 65.2                  
Fair Value, ending balance 65.9 [1],[4],[18],[28],[36]   65.2 [2],[3],[17],[30],[31]              
Investment, Identifier [Axis]: Wittur Holding GmbH | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[30],[31] 13.3                  
Fair Value, ending balance 13.4 [1],[4],[18],[28],[36]   13.3 [2],[3],[17],[30],[31]              
Investment, Identifier [Axis]: Wittur Holding GmbH, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 14.2 10.9 10.9              
Gross Additions 0.0 [11]   0.0 [12]              
Gross Reductions 0.0 [13]   0.0 [14]              
Net Realized Gain (Loss) 0.0   0.0              
Net Change in Unrealized Appreciation (Depreciation) 1.3   3.3              
Fair Value, ending balance 15.5   14.2              
Investment Income 0.0 [15]   0.0 [16]              
PIK Income 0.0 [15]   0.0 [16]              
Fee income 0.0 [15]   0.0 [16]              
Dividend and Other Income 0.0 [15]   0.0 [16]              
Investment, Identifier [Axis]: Wittur Holding GmbH, Common Stock | Capital Goods                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[30],[31] 14.2                  
Fair Value, ending balance 15.5 [1],[4],[18],[28],[29],[36]   14.2 [2],[3],[17],[26],[30],[31]              
Investment, Identifier [Axis]: Wood Group Receivables LLC (FKA John Wood Group PLC), Revolver | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 11.9                  
Fair Value, ending balance 11.8 [1],[4],[18],[36]   11.9 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Wood Group Receivables LLC (FKA John Wood Group PLC), Revolver | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 12.9                  
Fair Value, ending balance 12.8 [1],[4],[22],[36]   12.9 [2],[3],[21],[31]              
Investment, Identifier [Axis]: Woolpert Inc | Capital Goods 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 1.0                  
Fair Value, ending balance 2.3 [1],[4],[18]   1.0 [2],[3],[17]              
Investment, Identifier [Axis]: Woolpert Inc | Capital Goods 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[44] 10.7                  
Fair Value, ending balance 15.9 [1],[4],[18],[45]   10.7 [2],[3],[44]              
Investment, Identifier [Axis]: Woolpert Inc | Capital Goods 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 6.9                  
Fair Value, ending balance 5.6 [1],[4],[22]   6.9 [2],[3],[21]              
Investment, Identifier [Axis]: Woolpert Inc | Capital Goods 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 16.0                  
Fair Value, ending balance 10.7 [1],[4],[22]   16.0 [2],[3],[21]              
Investment, Identifier [Axis]: Worldwise Inc 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [60] 0.0 19.1 19.1              
Gross Additions [12],[60]     0.0              
Gross Reductions [14],[60]     (19.1)              
Net Realized Gain (Loss) [60]     0.0              
Net Change in Unrealized Appreciation (Depreciation) [60]     0.0              
Fair Value, ending balance [60]     0.0              
Investment Income [16],[60]     0.0              
PIK Income [16],[60]     0.0              
Fee income [16],[60]     0.0              
Dividend and Other Income [16],[60]     0.0              
Investment, Identifier [Axis]: Worldwise Inc 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.0 0.0              
Gross Additions [12]     0.0              
Gross Reductions [14]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.0              
Fair Value, ending balance     0.0              
Investment Income [16]     0.0              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Worldwise Inc | Household & Personal Products                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[27] 0.9                  
Fair Value, ending balance 1.1 [1],[4],[18],[29],[32]   0.9 [2],[3],[17],[26],[27]              
Investment, Identifier [Axis]: Worldwise Inc | Household & Personal Products 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[27] 4.7                  
Fair Value, ending balance 4.5 [1],[4],[18],[29],[32]   4.7 [2],[3],[17],[26],[27]              
Investment, Identifier [Axis]: Worldwise Inc | Household & Personal Products 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[26],[27] 0.9                  
Fair Value, ending balance 0.9 [1],[4],[18],[29],[32]   0.9 [2],[3],[17],[26],[27]              
Investment, Identifier [Axis]: Worldwise Inc | Household & Personal Products 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[26],[27] 0.8                  
Fair Value, ending balance 0.8 [1],[4],[22],[29],[32]   0.8 [2],[3],[21],[26],[27]              
Investment, Identifier [Axis]: Worldwise Inc, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.0 0.7 0.7              
Gross Additions [12]     0.0              
Gross Reductions [14]     0.0              
Net Realized Gain (Loss)     (0.6)              
Net Change in Unrealized Appreciation (Depreciation)     (0.1)              
Fair Value, ending balance     0.0              
Investment Income [16]     0.0              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: Xylem Kendall | Commercial & Professional Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33] 17.5                  
Fair Value, ending balance 17.5 [1],[4],[18],[34]   17.5 [2],[3],[17],[33]              
Investment, Identifier [Axis]: Xylem Kendall | Commercial & Professional Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 1.5                  
Fair Value, ending balance 2.0 [1],[4],[18]   1.5 [2],[3],[17]              
Investment, Identifier [Axis]: Xylem Kendall | Commercial & Professional Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 15.7                  
Fair Value, ending balance 15.8 [1],[4],[22]   15.7 [2],[3],[21]              
Investment, Identifier [Axis]: Xylem Kendall | Commercial & Professional Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 1.2                  
Fair Value, ending balance 0.7 [1],[4],[22]   1.2 [2],[3],[21]              
Investment, Identifier [Axis]: Zellis Holdings Ltd | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[31] 3.8                  
Fair Value, ending balance 4.5 [1],[4],[18],[36]   3.8 [2],[3],[17],[31]              
Investment, Identifier [Axis]: Zellis Holdings Ltd | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 4.4                  
Fair Value, ending balance 3.5 [1],[4],[22],[36]   4.4 [2],[3],[21],[31]              
Investment, Identifier [Axis]: Zendesk Inc | Software & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[33],[39] 68.4                  
Fair Value, ending balance 72.8 [1],[4],[18],[34],[37]   68.4 [2],[3],[17],[33],[39]              
Investment, Identifier [Axis]: Zendesk Inc | Software & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 5.0                  
Fair Value, ending balance 6.0 [1],[4],[22]   5.0 [2],[3],[21]              
Investment, Identifier [Axis]: Zendesk Inc | Software & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 6.0                  
Fair Value, ending balance [2],[3],[21]     6.0              
Investment, Identifier [Axis]: Zeus Industrial Products Inc | Health Care Equipment & Services 1                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[39] 79.0                  
Fair Value, ending balance 1.5 [1],[4],[18]   79.0 [2],[3],[17],[39]              
Investment, Identifier [Axis]: Zeus Industrial Products Inc | Health Care Equipment & Services 2                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17] 7.3                  
Fair Value, ending balance 85.5 [1],[4],[18],[37]   7.3 [2],[3],[17]              
Investment, Identifier [Axis]: Zeus Industrial Products Inc | Health Care Equipment & Services 3                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 11.0                  
Fair Value, ending balance 9.5 [1],[4],[22]   11.0 [2],[3],[21]              
Investment, Identifier [Axis]: Zeus Industrial Products Inc | Health Care Equipment & Services 4                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21] 7.3                  
Fair Value, ending balance [2],[3],[21]     7.3              
Investment, Identifier [Axis]: athenahealth Inc, Preferred Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 383.7 361.3 361.3              
Gross Additions 10.4 [5]   40.2 [6]              
Gross Reductions 0.0 [7]   (20.1) [8]              
Net Realized Gain (Loss) 0.0   0.4              
Net Change in Unrealized Appreciation (Depreciation) (5.3)   1.9              
Fair Value, ending balance 388.8   383.7              
Investment Income 0.0 [9]   0.0 [10]              
PIK Income 10.4 [9]   40.3 [10]              
Fee income 0.0 [9]   0.0 [10]              
Dividend and Other Income 0.0 [9]   0.0 [10]              
Investment, Identifier [Axis]: athenahealth Inc, Preferred Stock | Health Care Equipment & Services                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[17],[25] 383.7                  
Fair Value, ending balance 388.8 [1],[4],[18],[38]   383.7 [2],[3],[17],[25]              
Investment, Identifier [Axis]: gHM Dunn Co Inc, Common Stock                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 0.4 0.0 0.0              
Gross Additions [12]     0.0              
Gross Reductions [14]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     0.4              
Fair Value, ending balance     0.4              
Investment Income [16]     0.0              
PIK Income [16]     0.0              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: gHM Dunn Co Inc, Preferred Equity                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance 15.6 $ 0.0 0.0              
Gross Additions [12]     13.4              
Gross Reductions [14]     0.0              
Net Realized Gain (Loss)     0.0              
Net Change in Unrealized Appreciation (Depreciation)     2.2              
Fair Value, ending balance     15.6              
Investment Income [16]     0.0              
PIK Income [16]     0.9              
Fee income [16]     0.0              
Dividend and Other Income [16]     0.0              
Investment, Identifier [Axis]: iNova Pharmaceuticals (Australia) Pty Limited | Pharmaceuticals, Biotechnology & Life Sciences                    
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]                    
Fair Value, beginning balance [2],[3],[21],[31] 2.6                  
Fair Value, ending balance $ 2.5 [4],[22],[36]   $ 2.6 [2],[3],[21],[31]              
[1] Security may be an obligation of one or more entities affiliated with the named company.
[2] Security may be an obligation of one or more entities affiliated with the named company.
[3] See Note 8 for additional information regarding the fair value of the Company’s financial instruments.
[4] See Note 8 for additional information regarding the fair value of the Company’s financial instruments.
[5] Gross additions include increases in the cost basis of investments resulting from new portfolio investments, PIK interest, the amortization of unearned income, the exchange of one or more existing securities for one or more new securities and the movement of an existing portfolio company into this category from a different category.
[6] Gross additions include increases in the cost basis of investments resulting from new portfolio investments, PIK interest, the amortization of unearned income, the exchange of one or more existing securities for one or more new securities and the movement of an existing portfolio company into this category from a different category.
[7] Gross reductions include decreases in the cost basis of investments resulting from principal collections related to investment repayments or sales, the exchange of one or more existing securities for one or more new securities and the movement of an existing portfolio company out of this category into a different category.
[8] Gross reductions include decreases in the cost basis of investments resulting from principal collections related to investment repayments or sales, the exchange of one or more existing securities for one or more new securities and the movement of an existing portfolio company out of this category into a different category.
[9] Interest, PIK, Fee and Dividend and Other income presented for the three months ended March 31, 2026.
[10] Interest, PIK, fee and dividend and other income presented for the full year ended December 31, 2025.
[11] Gross additions include increases in the cost basis of investments resulting from new portfolio investments, PIK interest, the amortization of unearned income, the exchange of one or more existing securities for one or more new securities and the movement of an existing portfolio company into this category from a different category.
[12] Gross additions include increases in the cost basis of investments resulting from new portfolio investments, PIK interest, the amortization of unearned income, the exchange of one or more existing securities for one or more new securities and the movement of an existing portfolio company into this category from a different category.
[13] Gross reductions include decreases in the cost basis of investments resulting from principal collections related to investment repayments or sales, the exchange of one or more existing securities for one or more new securities and the movement of an existing portfolio company out of this category into a different category.
[14] Gross reductions include decreases in the cost basis of investments resulting from principal collections related to investment repayments or sales, the exchange of one or more existing securities for one or more new securities and the movement of an existing portfolio company out of this category into a different category.
[15] Interest, PIK, Fee and Dividend and Other income presented for the three months ended March 31, 2026.
[16] Interest, PIK, fee and dividend and other income presented for the full year ended December 31, 2025.
[17] Security or portion thereof is pledged as collateral supporting the amounts outstanding under the Senior Secured Revolving Credit Facility (see Note 9).
[18] Security or portion thereof is pledged as collateral supporting the amounts outstanding under the Senior Secured Revolving Credit Facility (see Note 9).
[19] Security or portion thereof held within CCT Tokyo Funding LLC and is pledged as collateral supporting the amounts outstanding under the revolving credit facility with Sumitomo Mitsui Banking Corporation (see Note 9).
[20] Security or portion thereof held within CCT Tokyo Funding LLC and is pledged as collateral supporting the amounts outstanding under the revolving credit facility with Sumitomo Mitsui Banking Corporation (see Note 9).
[21] Security is an unfunded commitment. Reflects the stated spread at the time of commitment, but may not be the actual rate received upon funding.
[22] Security is an unfunded commitment. Reflects the stated spread at the time of commitment, but may not be the actual rate received upon funding.
[23] The Company held this investment as of March 31, 2026 but it was not deemed to “control” the portfolio company as of March 31, 2026. Transfers in or out have been presented at amortized cost.
[24] The Company held this investment as of December 31, 2025 but it was not deemed to be in “control” of the portfolio company as of December 31, 2025. Transfers in or out have been presented at amortized cost.
[25] Under the Investment Company Act of 1940, as amended, the Company generally is deemed to be an “affiliated person” of a portfolio company if it owns 5% or more of the portfolio company’s voting securities and generally is deemed to “control” a portfolio company if it owns more than 25% of the portfolio company’s voting securities or it has the power to exercise control over the management or policies of such portfolio company. As of December 31, 2025, the Company held investments in portfolio companies of which it is deemed to be an “affiliated person” but is not deemed to “control”. The following table presents certain information with respect to investments in portfolio companies of which the Company was deemed to be an affiliated person for the year ended December 31, 2025:
Portfolio Company
Fair Value at December 31, 2024
Gross Additions(1)
Gross Reductions(2)
Net Realized Gain (Loss)Net Change in Unrealized Appreciation (Depreciation)
Fair Value at December 31, 2025
Interest Income(3)
PIK Income(3)
Fee Income(3)
Dividend and Other Income(3)
Senior Secured Loans—First Lien
48Forty Solutions LLC
$148.5 $6.3 $(0.4)$— $(68.4)$86.0 $1.7 $6.3 $— $— 
48Forty Solutions LLC
3.0 4.4 (0.7)— (3.8)2.9 0.2 — — — 
Affordable Care Inc35.2 13.6 (1.0)— (3.2)44.6 3.1 1.1 — — 
Affordable Care Inc22.2 0.7 — — (1.5)21.4 1.7 0.7 — — 
Belk Inc29.5 — (6.6)— 0.2 23.1 3.8 — — — 
Galaxy Universal LLC86.3 — (86.3)— — — 9.4 — 0.2 — 
Galaxy Universal LLC18.5 1.9 (20.4)— — — 2.1 — 0.1 — 
Galaxy Universal LLC— 45.5 (45.5)— — — 4.5 — 2.0 — 
Galaxy Universal LLC— 37.5 (37.5)— — — 3.1 — 1.1 — 
One Call Care Management Inc4.7 — (4.8)0.1 — — 0.4 — — — 
Senior Secured Loans—Second Lien
 Constellis Holdings LLC(4)
7.0 — (6.8)— (0.2)— — — — — 
Other Senior Secured Debt
 One Call Care Management Inc
25.1 2.4 — — 0.8 28.3 (0.1)2.6 — — 
Asset Based Finance
Accelerator Investments Aggregator LP, Private Equity
0.9 — (0.4)— 0.1 0.6 — — — — 
Altavair AirFinance, ABF Equity128.2 — (82.4)(1.0)3.8 48.6 — — — 20.0 
Bond Aviation Holdings LLC, Term Loan— 0.1 — — — 0.1 — — — — 
Bond Aviation Holdings LLC, Term Loan— 0.7 — — — 0.7 — — — — 
Bond Aviation Holdings LLC, ABF Equity— 4.9 — — — 4.9 0.1 — 0.2 — 
GreenSky Holdings LLC, ABF Equity14.9 — — — (0.4)14.5 — — — — 
GreenSky Holdings LLC, ABF Equity22.3 2.6 (8.4)— (1.2)15.3 — — — 3.6 
GreenSky Holdings LLC, Term Loan33.5 3.2 — — — 36.7 — 3.4 — — 
Equity/Other
48Forty Solutions LLC, Common Stock— — — — — — — — — — 
Affordable Care Inc, Preferred Stock73.1 9.9 — — (10.7)72.3 — 9.9 — — 
athenahealth Inc, Preferred Stock361.3 40.2 (20.1)0.4 1.9 383.7 — 40.3 — — 
Belk Inc, Common Stock27.1 4.2 — — 5.8 37.1 — — — — 
Constellis Holdings LLC, Private Equity— — — (10.3)10.3 — — — — — 
Portfolio Company
Fair Value at December 31, 2024
Gross Additions(1)
Gross Reductions(2)
Net Realized Gain (Loss)Net Change in Unrealized Appreciation (Depreciation)
Fair Value at December 31, 2025
Interest Income(3)
PIK Income(3)
Fee Income(3)
Dividend and Other Income(3)
Constellis Holdings LLC, Preferred Equity$3.4 $— $(3.2)$— $(0.2)$— $— $— $— $— 
Galaxy Universal LLC, Common Stock49.2 — (43.9)8.5 (13.8)— — — — — 
Galaxy Universal LLC, Trade Claim1.9 — (2.5)— 0.6 — — — — — 
Galaxy Universal LLC, Preferred Stock7.2 0.7 (5.6)— (2.3)— — 0.8 — — 
One Call Care Management Inc, Preferred Stock A20.7 — — — (3.2)17.5 — — — — 
One Call Care Management Inc, Common Stock1.9 — — — (1.0)0.9 — — — — 
One Call Care Management Inc, Preferred Stock B12.2 0.8 — — 0.2 13.2 — 0.9 — — 
Proserv Acquisition LLC, Class A Preferred Units2.2 — — — — 2.2 — — — — 
Total$1,140.0 $179.6 $(376.5)$(2.3)$(86.2)$854.6 $30.0 $66.0 $3.6 $23.6 
[26] Security is non-income producing.
[27] Asset is on non-accrual status.
[28] Under the Investment Company Act of 1940, as amended, the Company generally is deemed to “control” a portfolio company if it owns more than 25% of the portfolio company’s voting securities or it has the power to exercise control over the management or policies of such portfolio company. As of March 31, 2026, the Company held investments in portfolio companies of which it is deemed to be an “affiliated person” and deemed to “control”. The following table presents certain information with respect to investments in portfolio companies of which the Company was deemed to be an affiliated person and deemed to control for the three months ended March 31, 2026:
Portfolio Company
Fair Value at December 31, 2025
Gross Additions(1)
Gross Reductions(2)
Net Realized Gain (Loss)Net Change in Unrealized Appreciation (Depreciation)
Fair Value at March 31, 2026
Interest Income(3)
PIK Income(3)
Fee Income(3)
Dividend and Other Income(3)
Senior Secured Loans—First Lien
 48Forty Solutions LLC(4)
$— $15.8 $— $— $0.5 $16.3 $0.3 $— $— $— 
 48Forty Solutions LLC(4)
— 20.2 — — 0.6 20.8 0.4 — — — 
 Alacrity Solutions Group LLC 10.7 0.1 (7.1)0.1 (0.1)3.7 — 0.1 — — 
 Alacrity Solutions Group LLC 0.1 — (0.1)0.1 (0.1)— — — — — 
 ATX Networks Corp 27.9 1.0 — — — 28.9 — 1.1 — — 
 ATX Networks Corp 93.0 1.0 — — (21.5)72.5 — — — — 
 Gracent LLC 28.4 (0.1)— — (1.5)26.8 — — — — 
 HM Dunn Co Inc
19.2 — — — — 19.2 0.5 — — — 
 HM Dunn Co Inc
4.0 1.0 — — — 5.0 0.1 — — — 
 Kellermeyer Bergensons Services LLC
220.3 5.4 (0.5)— (0.2)225.0 — 5.3 — — 
 Kellermeyer Bergensons Services LLC 40.3 0.1 — — (27.3)13.1 — — — — 
 Lionbridge Technologies Inc — 55.5 (5.6)— — 49.9 — 0.8 — — 
 Lionbridge Technologies Inc — 53.8 — — (27.9)25.9 — — — — 
 NCI Inc 30.7 — (0.4)— 0.1 30.4 0.5 — — — 
 Production Resource Group LLC 273.5 17.8 — — 0.7 292.0 — 8.0 — — 
 Wittur Holding GmbH 65.2 2.0 — — (1.3)65.9 0.2 0.8 — — 
 Wittur Holding GmbH 13.3 0.8 — — (0.7)13.4 0.4 0.2 — — 
Senior Secured Loans—Second Lien
Quoizel, LLC6.8 — — — (0.3)6.5 0.2 — — — 
Quoizel, LLC7.1 — — — (0.3)6.8 0.2 — — — 
Subordinated Debt
Accuride Corp6.4 0.1 — — (0.5)6.0 — 0.1 — — 
Alacrity Solutions Group LLC3.8 0.1 — — (0.6)3.3 — 0.1 — — 
ATX Networks Corp3.9 — — — (3.9)— — — — — 
Asset Based Finance
 801 5th Ave, Seattle, Structure Mezzanine 49.8 0.1 — — (3.5)46.4 1.5 — — — 
 801 5th Ave, Seattle, ABF Equity — — — — — — — — — — 
 Abacus JV, ABF Equity 0.8 — — — — 0.8 — — — — 
AOP SFR 1 LLC (FKA Avenue One PropCo), ABF Equity6.3 0.2 — — (1.4)5.1 — — — — 
AOP SFR 1 LLC (FKA Avenue One PropCo), Term Loan34.7 0.6 — — — 35.3 — 0.6 — — 
 Australis Maritime, Common Stock 1.2 — — — 0.2 1.4 — — — — 
 Australis Maritime II, ABF Equity 23.3 — — — 0.3 23.6 — — — — 
 Avida Holding AB, Common Stock 51.7 — — — (4.2)47.5 — — — — 
 Avida Holding AB, Subordinated Bond 1.6 — — — — 1.6 — — — — 
 Capital Automotive LP, ABF Equity 23.0 — (0.2)— 0.9 23.7 — — — 0.3 
Portfolio Company
Fair Value at December 31, 2025
Gross Additions(1)
Gross Reductions(2)
Net Realized Gain (Loss)Net Change in Unrealized Appreciation (Depreciation)
Fair Value at March 31, 2026
Interest Income(3)
PIK Income(3)
Fee Income(3)
Dividend and Other Income(3)
 Capital Automotive LP, Structured Mezzanine $18.7 $— $(0.3)$— $(0.1)$18.3 $0.5 $— $— $— 
 Galaxy Container, ABF Equity 0.2 — — — — 0.2 — — — — 
 Galaxy Container, Bond — 0.2 — — — 0.2 — — — — 
 Kilter Finance 2.0, Common Stock
— 4.0 — — — 4.0 — — — — 
 Kilter Finance, Preferred Stock 88.4 0.8 — — — 89.2 1.9 0.8 — — 
 Kilter Finance, ABF Equity 3.0 — — — (0.3)2.7 — — — — 
 Kilter Finance, Common Stock — — — — — — — — — — 
 KKR Altitude II Offshore Aggregator LP, Partnership Interest 115.7 — — — 0.3 116.0 — — — 3.1 
 KKR Central Park Leasing Aggregator L.P., Partnership Interest 27.0 — — — — 27.0 — — — — 
 KKR Chord IP Aggregator LP, Partnership Interest 0.1 — — — — 0.1 — — — — 
 KKR Rocket Loans Aggregator LLC, Partnership Interest 2.0 — (0.2)— (0.1)1.7 — — — — 
 KKR Zeno Aggregator LP (K2 Aviation), Partnership Interest 1.0 — — — (0.8)0.2 — — — 1.2 
 KSC I Aircraft LP, ABF Equity 5.8 4.3 — — — 10.1 — — — — 
 My Community Homes PropCo 2, ABF Equity 11.8 — — — (9.7)2.1 — — — — 
 My Community Homes PropCo 2, Term Loan 69.4 1.3 — — — 70.7 — 1.3 — — 
 My Community Homes PropCo 2, Term Loan 4.2 0.1 — — — 4.3 — 0.1 — — 
 My Community Homes PropCo 2, Term Loan 22.3 0.4 — — — 22.7 — 0.4 — — 
 Prime St LLC, ABF Equity — — — — — — — — — — 
 Prime St LLC, Structured Mezzanine 23.7 — — — (1.5)22.2 0.9 — — — 
 Roemanu LLC, ABF Equity
197.2 — — — 0.1 197.3 — — — — 
 Sallie Mae Levered, ABF Equity 1.1 1.4 (0.4)— 0.1 2.2 — — — — 
 Sallie Mae Levered, Bond 4.3 — — — — 4.3 0.1 — — — 
 Sallie Mae Levered, Term Loan 0.1 0.2 — — — 0.3 — — — — 
 Sallie Mae Levered, Bond — 4.3 — — — 4.3 0.1 — — — 
 Sallie Mae Levered, Bond — 1.2 — — — 1.2 — — — — 
 Sallie Mae Levered, Bond — 0.6 — — — 0.6 — — — — 
 TDC LLP, Preferred Equity 12.5 3.6 — — (0.4)15.7 0.4 — — — 
 TDC LLP, ABF Equity — — — — — — — — — — 
Credit Opportunities Partners JV, LLC
Credit Opportunities Partners JV, LLC1,967.9 — (189.0)(28.8)(43.4)1,706.7 — — — 62.7 
Equity/Other
 48Forty Solutions LLC, Preferred Stock — 55.6 — — (10.1)45.5 — — — — 
 48Forty Solutions LLC, Common Stock(4)
— 0.5 — — (0.5)— — — — — 
 Accuride Corp, Common Stock — — — — — — — — — — 
 Accuride Corp, Preferred Stock — — — — — — — — — — 
 Alacrity Solutions Group LLC, Common Stock — — — — — — — — — — 
 Alacrity Solutions Group LLC, Preferred Equity 0.7 — — — (0.6)0.1 — — — — 
Portfolio Company
Fair Value at December 31, 2025
Gross Additions(1)
Gross Reductions(2)
Net Realized Gain (Loss)Net Change in Unrealized Appreciation (Depreciation)
Fair Value at March 31, 2026
Interest Income(3)
PIK Income(3)
Fee Income(3)
Dividend and Other Income(3)
 ATX Networks Corp, Common Stock $— $— $— $(9.9)$9.9 $— $— $— $— $— 
 ATX Networks Corp, Class B-1 Common Stock — — — (5.0)5.0 — — — — — 
 ATX Networks Corp, Class B-2 Common Stock — — — (4.0)4.0 — — — — — 
 Borden (New Dairy Opco), Common Stock 11.1 — — — (0.6)10.5 — — — — 
 Gracent LLC, Preferred Stock B — — — — — — — — — — 
 Gracent LLC, Class A Common Stock — — — — — — — — — — 
 Gracent LLC, Preferred Equity — — — (8.2)8.2 — — — — — 
 HM Dunn Co Inc, Preferred Equity
15.6 0.5 — — 1.9 18.0 — 0.6 — — 
 HM Dunn Co Inc, Common Stock
0.4 — — — 1.2 1.6 — — — — 
 JW Aluminum Co, Preferred Stock 170.4 — — — 34.2 204.6 — — — — 
 Kellermeyer Bergensons Services LLC, Common Stock — — — — — — — — — — 
 Kellermeyer Bergensons Services LLC, Preferred Stock — — — — — — — — — — 
 Lionbridge Technologies Inc, Preferred Stock — — — — — — — — — — 
 Lionbridge Technologies Inc, Common Equity — — — — — — — — — — 
 NCI Inc, Class A-1 Common Stock — — — — — — — — — — 
 NCI Inc, Class B-1 Common Stock — — — — — — — — — — 
 NCI Inc, Class C Common Stock 38.7 — — — 6.7 45.4 — — — — 
 NCI Inc, Class I-1 Common Stock — — — — — — — — — — 
 Quoizel, LLC, Common Stock 2.7 — — — (0.8)1.9 — — — — 
 Production Resource Group LLC, Common Stock 95.3 — — — (60.0)35.3 — — — — 
 Quorum Health Corp, Trade Claim 0.5 — — — — 0.5 — — — — 
 Quorum Health Corp, Trust Initial Funding Units 0.1 — — — — 0.1 — — — — 
 Quorum Health Corp, Private Equity 10.0 — — — 0.1 10.1 — — — — 
 Quorum Health Corp, Private Equity 7.4 — — — 0.1 7.5 — — — — 
 Wittur Holding GmbH, Common Stock 14.2 — — — 1.3 15.5 — — — — 
Total$3,990.5 $254.5 $(203.8)$(55.7)$(147.8)$3,837.7 $8.2 $20.3 $— $67.3 
[29] Security is non-income producing.
[30] Under the Investment Company Act of 1940, as amended, the Company generally is deemed to “control” a portfolio company if it owns more than 25% of the portfolio company’s voting securities or it has the power to exercise control over the management or policies of such portfolio company. As of December 31, 2025, the Company held investments in portfolio companies of which it is deemed to be an “affiliated person” and deemed to “control”. During the year ended December 31, 2025, the Company disposed of investments in portfolio companies of which it was deemed to be an “affiliated person” and deemed to “control”. The following table presents certain information with respect to investments in portfolio companies of which the Company was deemed to be an affiliated person and deemed to control for the year ended December 31, 2025:
Portfolio Company
Fair Value at December 31, 2024
Gross Additions(1)
Gross Reductions(2)
Net Realized Gain (Loss)Net Change in Unrealized Appreciation (Depreciation)
Fair Value at December 31, 2025
Interest Income(3)
PIK Income(3)
Fee Income(3)
Dividend and Other Income(3)
Senior Secured Loans—First Lien
Alacrity Solutions Group LLC$— $10.6 $— $— $0.1 $10.7 $0.6 $0.3 $— $— 
Alacrity Solutions Group LLC— — — — 0.1 0.1 — — — — 
ATX Networks Corp37.0 1.1 (37.5)— (0.6)— — 1.0 — — 
ATX Networks Corp15.3 12.6 — — — 27.9 — 2.3 — — 
ATX Networks Corp50.6 43.0 — — (0.6)93.0 0.2 9.1 1.1 — 
Gracent LLC29.6 4.7 — — (5.9)28.4 1.0 3.7 — — 
HM Dunn Co Inc
34.8 — (13.1)(2.5)— 19.2 2.8 — — — 
HM Dunn Co Inc
3.4 2.6 (2.0)— — 4.0 0.5 — — — 
Kellermeyer Bergensons Services LLC201.6 21.5 (1.9)— (0.9)220.3 0.8 20.7 — — 
Kellermeyer Bergensons Services LLC87.7 5.9 — — (53.3)40.3 — 3.9 — — 
NCI Inc32.1 — (1.4)— — 30.7 3.8 — — — 
Production Resource Group LLC195.9 — (192.0)— (3.9)— 1.3 6.9 — — 
Production Resource Group LLC0.3 — (0.2)— (0.1)— — — — — 
Production Resource Group LLC67.7 — (65.7)— (2.0)— 1.0 3.2 — — 
Portfolio Company
Fair Value at December 31, 2024
Gross Additions(1)
Gross Reductions(2)
Net Realized Gain (Loss)Net Change in Unrealized Appreciation (Depreciation)
Fair Value at December 31, 2025
Interest Income(3)
PIK Income(3)
Fee Income(3)
Dividend and Other Income(3)
Production Resource Group LLC$37.2 $— $(36.0)$— $(1.2)$— $0.5 $1.8 $— $— 
Production Resource Group LLC107.4 — (104.3)— (3.1)— 1.6 5.1 — — 
Production Resource Group LLC— — — — — — 0.1 0.3 — — 
Production Resource Group LLC— — — — — — 0.2 — — — 
Production Resource Group LLC— 263.9 — — 9.6 273.5 0.1 7.1 — — 
Wittur Holding GmbH54.1 3.8 — — 7.3 65.2 0.7 3.1 — — 
Wittur Holding GmbH— 6.3 — — 7.0 13.3 1.0 0.4 — — 
Worldwise Inc(4)
19.1 — (19.1)— — — — — — — 
Worldwise Inc— — — — — — — — — — 
Senior Secured Loans—Second Lien
Quoizel, LLC7.1 — — — (0.3)6.8 0.8 — — — 
Quoizel, LLC7.4 — — — (0.3)7.1 0.8 — — — 
Other Senior Secured Debt
JW Aluminum Co76.6 — (76.4)0.3 (0.5)— 1.9 — — — 
Subordinated Debt
Accuride Corp— 4.3 — — 2.1 6.4 0.1 0.1 — — 
Alacrity Solutions Group LLC— 3.8 — — — 3.8 — 0.4 — — 
ATX Networks Corp32.9 — — — (29.0)3.9 — — — — 
Asset Based Finance
801 5th Ave, Seattle, Structure Mezzanine54.5 2.1 — — (6.8)49.8 6.2 1.9 — — 
801 5th Ave, Seattle, ABF Equity— — (0.1)— 0.1 — — — — — 
Abacus JV, ABF Equity24.6 — (27.0)0.7 2.5 0.8 — — — — 
Australis Maritime, Common Stock11.3 — (10.3)— 0.2 1.2 — — — 0.2 
Australis Maritime II, ABF Equity19.8 9.8 (7.0)— 0.7 23.3 — — — 1.4 
Avenue One PropCo, ABF Equity10.2 — — — (3.9)6.3 — — — — 
Avenue One PropCo, Term Loan32.3 2.4 — — — 34.7 — 2.4 — — 
Avida Holding AB, Common Stock60.4 — — — (8.7)51.7 — — — — 
Avida Holding AB, Subordinated Bond1.3 — — — 0.3 1.6 0.2 — — — 
Capital Automotive LP, ABF Equity32.9 — (17.8)6.7 1.2 23.0 — — — 1.7 
Capital Automotive LP, Structured Mezzanine40.1 — (21.4)0.1 (0.1)18.7 2.8 — — — 
Discover Financial Services, Subordinated Loan38.8 — (38.8)— — — 2.7 — — — 
Discover Financial Services, ABF Equity21.7 — (21.4)0.5 (0.8)— — — — 1.3 
Galaxy Container, ABF Equity— 0.2 — — — 0.2 — — — — 
Kilter Finance, Preferred Stock85.4 18.6 (15.6)— — 88.4 6.1 3.8 — — 
Kilter Finance, ABF Equity0.5 — — — 2.5 3.0 — — — — 
KKR Altitude II Offshore Aggregator LP, Partnership Interest146.7 27.6 (62.0)3.9 (0.5)115.7 — — — 15.2 
KKR Central Park Leasing Aggregator L.P., Partnership Interest15.8 — — — 11.2 27.0 — — — — 
KKR Chord IP Aggregator LP, Partnership Interest0.1 — — — — 0.1 — — — 0.2 
Portfolio Company
Fair Value at December 31, 2024
Gross Additions(1)
Gross Reductions(2)
Net Realized Gain (Loss)Net Change in Unrealized Appreciation (Depreciation)
Fair Value at December 31, 2025
Interest Income(3)
PIK Income(3)
Fee Income(3)
Dividend and Other Income(3)
KKR Rocket Loans Aggregator LLC, Partnership Interest$4.3 $— $(2.9)$— $0.6 $2.0 $— $— $— $— 
KKR Zeno Aggregator LP (K2 Aviation), Partnership Interest7.2 — (2.9)0.3 (3.6)1.0 — — — 7.2 
KSC I Aircraft LP, ABF Equity— 5.8 — — — 5.8 — — — — 
My Community Homes PropCo 2, ABF Equity15.6 6.7 — — (10.5)11.8 — — — — 
My Community Homes PropCo 2, Term Loan64.4 5.0 — — — 69.4 — 5.1 — — 
My Community Homes PropCo 2, Term Loan— 4.2 — — — 4.2 — 0.2 — — 
My Community Homes PropCo 2, Term Loan— 22.3 — — — 22.3 — 0.9 — — 
Prime St LLC, ABF Equity— — (1.1)(0.8)1.9 — — — — — 
Prime St LLC, Structured Mezzanine27.6 4.0 — — (7.9)23.7 3.7 3.7 — — 
Roemanu LLC (FKA Toorak Capital Partners LLC), ABF Equity238.9 — (13.6)— (28.1)197.2 — — — 9.4 
Sallie Mae Levered, ABF Equity— 1.1 — — — 1.1 — — — — 
Sallie Mae Levered, Bond— 4.3 — — — 4.3 — — — — 
Sallie Mae Levered, Term Loan— 0.1 — — — 0.1 — — — — 
TDC LLP, Preferred Equity36.8 15.9 (41.9)1.0 0.7 12.5 1.5 — — — 
TDC LLP, ABF Equity1.9 — (2.0)— 0.1 — — — — — 
Credit Opportunities Partners JV, LLC
Credit Opportunities Partners JV, LLC1,363.3 630.2 — — (25.6)1,967.9 — — — 232.5 
Equity/Other
Accuride Corp, Common Stock— — — — — — — — — — 
Accuride Corp, Preferred Stock— — — — — — — — — — 
Alacrity Solutions Group LLC, Common Stock— 1.9 — — (1.9)— — — — — 
Alacrity Solutions Group LLC, Preferred Equity— 2.3 — — (1.6)0.7 — 0.2 — — 
ATX Networks Corp, Common Stock— — — — — — — — — — 
ATX Networks Corp, Class B-1 Common Stock— — — — — — — — — — 
ATX Networks Corp, Class B-2 Common Stock— — — — — — — — — — 
Borden (New Dairy Opco), Common Stock18.4 — — — (7.3)11.1 — — — — 
Gracent LLC, Preferred Stock B— — — — — — — — — — 
Gracent LLC, Class A Common Stock— — — — — — — — — — 
Gracent LLC, Preferred Equity5.0 — — — (5.0)— — — — — 
HM Dunn Co Inc, Preferred Stock, Series A0.1 — — (7.1)7.0 — — — — — 
HM Dunn Co Inc, Preferred Stock, Series B— — — — — — — — — — 
HM Dunn Co Inc, Preferred Equity
— 13.4 — — 2.2 15.6 — 0.9 — — 
HM Dunn Co Inc, Common Stock
— — — — 0.4 0.4 — — — — 
JW Aluminum Co, Common Stock2.5 — — — (2.5)— — — — — 
JW Aluminum Co, Preferred Stock152.3 — (156.4)(58.1)62.2 — — — — — 
JW Aluminum Co, Preferred Stock— 135.2 (10.4)— 45.6 170.4 — — — 14.3 
Kellermeyer Bergensons Services LLC, Common Stock— — — — — — — — — — 
Portfolio Company
Fair Value at December 31, 2024
Gross Additions(1)
Gross Reductions(2)
Net Realized Gain (Loss)Net Change in Unrealized Appreciation (Depreciation)
Fair Value at December 31, 2025
Interest Income(3)
PIK Income(3)
Fee Income(3)
Dividend and Other Income(3)
Kellermeyer Bergensons Services LLC, Preferred Stock$15.1 $— $— $— $(15.1)$— $— $— $— $— 
Kilter Finance, Common Stock— — — — — — — — — — 
NCI Inc, Class A-1 Common Stock— — — — — — — — — — 
NCI Inc, Class B-1 Common Stock— — — — — — — — — — 
NCI Inc, Class C Common Stock33.1 — — — 5.6 38.7 — — — — 
NCI Inc, Class I-1 Common Stock— — — — — — — — — — 
Production Resource Group LLC, Preferred Stock, Series A PIK67.2 — — (18.1)(49.1)— — — — — 
Production Resource Group LLC, Preferred Stock, Series B PIK— — — — — — — — — — 
Quoizel, LLC, Common Stock6.1 — — — (3.4)2.7 — — — — 
Production Resource Group LLC, Common Stock— 95.3 — — — 95.3 — — — — 
Quorum Health Corp, Trade Claim0.9 — — — (0.4)0.5 — — — — 
Quorum Health Corp, Trust Initial Funding Units0.1 — — — — 0.1 — — — — 
Quorum Health Corp, Private Equity10.1 0.9 — — (1.0)10.0 — — — — 
Quorum Health Corp, Private Equity— 2.1 — — 5.3 7.4 — — — — 
Wittur Holding GmbH, Common Stock10.9 — — — 3.3 14.2 — — — — 
Worldwise Inc, Common Stock0.7 — — (0.6)(0.1)— — — — — 
Total
$3,776.7 $1,395.5 $(1,002.2)$(73.7)$(105.8)$3,990.5 $43.0 $88.5 $1.1 $283.4 
[31] The investment is not a qualifying asset under the Investment Company Act of 1940, as amended. A business development company may not acquire any asset other than qualifying assets, unless, at the time the acquisition is made, qualifying assets represent at least 70% of the company’s total assets. As of December 31, 2025, 70.6% of the Company’s total assets represented qualifying assets.
[32] Asset is on non-accrual status.
[33] Security or portion thereof held within KKR - FSK CLO 3 LLC (see Note 9).
[34] Security or portion thereof held within KKR - FSK CLO 3 LLC (see Note 9).
[35] Security or portion thereof held within Juniata River LLC and is pledged as collateral supporting the amounts outstanding under a term loan credit facility with JPMorgan Chase Bank, N.A.
[36] The investment, or a portion of the investment is not a qualifying asset under the Investment Company Act of 1940, as amended. A business development company may not acquire any asset other than qualifying assets, unless, at the time the acquisition is made, qualifying assets represent at least 70% of the company’s total assets. As of March 31, 2026, 74.2% of the Company’s total assets represented qualifying assets.
[37] Security or portion thereof held within KKR - FSK CLO 2 LLC (see Note 9).
[38] Under the Investment Company Act of 1940, as amended, the Company generally is deemed to be an “affiliated person” of a portfolio company if it owns 5% or more of the portfolio company’s voting securities and generally is deemed to “control” a portfolio company if it owns more than 25% of the portfolio company’s voting securities or it has the power to exercise control over the management or policies of such portfolio company. As of March 31, 2026, the Company held investments in portfolio companies of which it is deemed to be an “affiliated person” but is not deemed to “control”. The following table presents certain information with respect to investments in portfolio companies of which the Company was deemed to be an affiliated person for the three months ended March 31, 2026:
Portfolio Company
Fair Value at December 31, 2025
Gross Additions(1)
Gross Reductions(2)
Net Realized Gain (Loss)Net Change in Unrealized Appreciation (Depreciation)
Fair Value at March 31, 2026
Interest Income(3)
PIK Income(3)
Fee Income(3)
Dividend and Other Income(3)
Senior Secured Loans—First Lien
48Forty Solutions LLC(4)
$86.0 $— $(85.7)$(93.8)$93.5 $— $— $— $— $— 
48Forty Solutions LLC(4)
2.9 — (4.1)(4.2)5.4 — — — — — 
Portfolio Company
Fair Value at December 31, 2025
Gross Additions(1)
Gross Reductions(2)
Net Realized Gain (Loss)Net Change in Unrealized Appreciation (Depreciation)
Fair Value at March 31, 2026
Interest Income(3)
PIK Income(3)
Fee Income(3)
Dividend and Other Income(3)
Affordable Care Inc$11.8 $— $— $— $(2.6)$9.2 $— $— $— $— 
Affordable Care Inc54.2 — — — (11.9)42.3 — — — — 
Belk Inc23.1 — (2.7)— — 20.4 0.8 — — — 
Other Senior Secured Debt
 One Call Care Management Inc 28.3 0.1 — — 4.4 32.8 — 0.7 — — 
Asset Based Finance
 Accelerator Investments Aggregator LP, ABF Equity 0.6 — — — — 0.6 — — — — 
 Altavair AirFinance, ABF Equity 48.6 — (11.6)— 0.4 37.4 — — — 1.2 
 Bond Aviation Holdings LLC, ABF Equity
0.1 — — — — 0.1 — — — — 
 Bond Aviation Holdings LLC, Term Loan 0.7 — — — — 0.7 — — — — 
 Bond Aviation Holdings LLC, Term Loan
4.9 6.6 — — — 11.5 0.2 — — — 
 GreenSky Holdings LLC, ABF Equity 14.5 — — — 0.4 14.9 — — — — 
 GreenSky Holdings LLC, ABF Equity 15.3 — (1.8)— 0.9 14.4 — — — 0.4 
 GreenSky Holdings LLC, Term Loan 36.7 — (3.6)— — 33.1 — 0.8 — — 
Equity/Other
 48Forty Solutions LLC, Common Stock(4)
— — — — — — — — — — 
 Affordable Care Inc, Preferred Stock 72.3 — — — (70.6)1.7 — — — — 
 athenahealth Inc, Preferred Stock 383.7 10.4 — — (5.3)388.8 — 10.4 — — 
 Belk Inc, Common Stock 37.1 — — — (3.5)33.6 — — — — 
 One Call Care Management Inc, Preferred Stock A 17.5 — — — 0.8 18.3 — — — — 
 One Call Care Management Inc, Common Stock 0.9 — — — — 0.9 — — — — 
 One Call Care Management Inc, Preferred Stock B 13.2 — — — (1.9)11.3 — — — — 
 Proserv Acquisition LLC, Class A Preferred Units 2.2 — — — — 2.2 — — — — 
Total$854.6 $17.1 $(109.5)$(98.0)$10.0 $674.2 $1.0 $11.9 $— $1.6 
[39] Security or portion thereof held within KKR - FSK CLO 2 LLC (see Note 9).
[40] Security or portion thereof held within Meadowbrook Run LLC and is pledged as collateral supporting the amounts outstanding under a revolving credit facility with Morgan Stanley Senior Funding, Inc. (see Note 9).
[41] Security or portion thereof held within Meadowbrook Run LLC and is pledged as collateral supporting the amounts outstanding under a revolving credit facility with Morgan Stanley Senior Funding, Inc. (see Note 9).
[42] Security is classified as Level 1 or Level 2 in the Company’s fair value hierarchy (see Note 8).
[43] Security is classified as Level 1 or Level 2 in the Company’s fair value hierarchy (see Note 8).
[44] Security or portion thereof held within Callowhill Street Funding LLC. and is pledged as collateral supporting the amounts outstanding under a revolving credit facility with CIBC Bank (see Note 9).
[45] Security or portion thereof held within Callowhill Street Funding LLC. and is pledged as collateral supporting the amounts outstanding under a revolving credit facility with CIBC Bank (see Note 9).
[46] Security held within CCT Holdings II LLC, a wholly-owned subsidiary of the Company.
[47] Security held within FSIC II Investments, Inc., a wholly-owned subsidiary of the Company.
[48] Security held within CCT Holdings II LLC, a wholly-owned subsidiary of the Company.
[49] Security held within FSIC II Investments, Inc., a wholly-owned subsidiary of the Company.
[50] Security or portion thereof held within Race Street Funding LLC. Security is available as collateral to support the amounts outstanding under the Senior Secured Revolving Credit Facility (see Note 9).
[51] Security or portion thereof held within Race Street Funding LLC. Security is available as collateral to support the amounts outstanding under the Senior Secured Revolving Credit Facility (see Note 9).
[52] Position or portion thereof unsettled as of unsettled as of December 31, 2025.
[53] The Company held this investment as of December 31, 2024 but it was not deemed to be an “affiliated person” of the portfolio company as of December 31, 2024. Transfers in or out have been presented at amortized cost.
[54] Security held within FSIC Investments, Inc., a wholly-owned subsidiary of the Company.
[55] Security or portion thereof held within Cobbs Creek LLC and is pledged as collateral supporting the amounts outstanding under the Senior Secured Revolving Credit Facility.
[56] Security or portion thereof held within Cobbs Creek LLC and is pledged as collateral supporting the amounts outstanding under the Senior Secured Revolving Credit Facility.
[57] Security held within IC Northern Investments, LLC, a wholly-owned subsidiary of the Company.
[58] Security held within IC Northern Investments, LLC, a wholly-owned subsidiary of the Company.
[59] Security held within FSIC Investments, Inc., a wholly-owned subsidiary of the Company.
[60] The Company held this investment as of December 31, 2024 but it was not deemed to be an “control” of the portfolio company as of December 31, 2024. Transfers in or out have been presented at amortized cost.