v3.26.3
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)
$ in Thousands
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2026
USD ($)
investment
Sep. 30, 2025
Sep. 30, 2026
USD ($)
investment
company
segment
Sep. 30, 2025
company
Sep. 30, 2026
USD ($)
investment
company
Dec. 31, 2025
USD ($)
Schedule of Investments [Line Items]            
Cash equivalents $ 15,400   $ 15,400   $ 15,400 $ 3,200
Cash exceeded federal deposit insurance corporation insurance protection levels 83,700   83,700   83,700 35,400
Fair value 5,800,369 [1],[2],[3]   5,800,369 [1],[2],[3]   5,800,369 [1],[2],[3] 5,518,117 [4],[5],[6]
Cost $ 4,958,925 [1],[3],[7]   $ 4,958,925 [1],[3],[7]   4,958,925 [1],[3],[7] 4,724,528 [4],[6],[8]
Percentage of total investment income, attributable to noncash paid-in-kind interest income (as a percent) 3.70% 3.00% 3.10% 2.70%    
Percentage of total investment come, attributable to noncash cumulative dividend income (as a percent) 0.80% 0.70% 0.80% 0.70%    
Percentage of total investment income, attributable to interest income, debt investments, net (as a percent) 1.70% 1.70% 1.60% 1.70%    
Number of operating segments | segment     1      
Number of reportable segments | segment     1      
Revolving Credit Facility | Line of Credit            
Schedule of Investments [Line Items]            
Commitment fee (as a percentage)     3.40%      
Non-accrual Status            
Schedule of Investments [Line Items]            
Fair value $ 54,700   $ 54,700   54,700 56,300
Cost 175,100   $ 175,100   $ 175,100 $ 155,300
Investment Owned, At Fair Value | Investment Type Concentration Risk            
Schedule of Investments [Line Items]            
Concentration risk (as a percent)     100.00%     100.00%
Investment Owned, At Fair Value | Investment Type Concentration Risk | Non-accrual Status            
Schedule of Investments [Line Items]            
Concentration risk (as a percent)     0.90%     1.00%
Investment Owned, At Cost | Investment Type Concentration Risk            
Schedule of Investments [Line Items]            
Concentration risk (as a percent)     100.00%     100.00%
Investment Owned, At Cost | Investment Type Concentration Risk | Non-accrual Status            
Schedule of Investments [Line Items]            
Concentration risk (as a percent)     3.50%     3.30%
LMM portfolio investments            
Schedule of Investments [Line Items]            
Consultation period subsequent to initial investment (in months)     12 months      
Investment company, number of portfolio companies with annual third-party appraisal was obtained, reviewed and certified | company     20 18 76  
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified (as a percent)         98.00%  
Fair value 3,250,100   $ 3,250,100   $ 3,250,100 $ 3,057,000
Cost $ 2,530,200   $ 2,530,200   $ 2,530,200 2,419,300
LMM portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk            
Schedule of Investments [Line Items]            
Concentration risk (as a percent)     25.00% 27.00% 94.00%  
Excluding investment company, number of portfolio companies | investment 3   3   3  
Private Loan portfolio investments            
Schedule of Investments [Line Items]            
Consultation period subsequent to initial investment (in months)     12 months      
Investment company, number of portfolio companies with annual third-party appraisal was obtained, reviewed and certified | company     16 14 64  
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified (as a percent)         93.00%  
Fair value $ 2,107,300   $ 2,107,300   $ 2,107,300 1,988,400
Cost $ 2,129,500   $ 2,129,500   $ 2,129,500 $ 2,014,100
Private Loan portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk            
Schedule of Investments [Line Items]            
Concentration risk (as a percent)     23.00% 26.00% 83.00%  
Excluding investment company, number of portfolio companies | investment 5   5   5  
Middle Market portfolio investments            
Schedule of Investments [Line Items]            
Percentage of portfolio investments containing limited consultation with financial advisory services firm (as a percent) 90.00%   90.00%   90.00% 95.00%
Fair value $ 73,500   $ 73,500   $ 73,500 $ 83,500
Cost 113,000   $ 113,000   113,000 $ 120,100
Middle Market portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk            
Schedule of Investments [Line Items]            
Concentration risk (as a percent)     1.30%     1.50%
Middle Market portfolio investments | Investment Owned, At Cost | Investment Type Concentration Risk            
Schedule of Investments [Line Items]            
Concentration risk (as a percent)     2.30%     2.50%
Other Portfolio investments            
Schedule of Investments [Line Items]            
Fair value 146,700   $ 146,700   146,700 $ 134,100
Cost $ 156,700   $ 156,700   $ 156,700 $ 141,600
Other Portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk            
Schedule of Investments [Line Items]            
Concentration risk (as a percent)     2.50%     2.40%
Other Portfolio investments | Investment Owned, At Cost | Investment Type Concentration Risk            
Schedule of Investments [Line Items]            
Concentration risk (as a percent)     3.20%     3.00%
[1] All portfolio company headquarters are based in the U.S., unless otherwise noted.
[2] Investment Fair Value was determined using significant unobservable inputs, unless otherwise noted. See Note C — Fair Value Hierarchy for Investments —Portfolio Composition for further discussion. Negative fair value is the result of the capitalized discount on the loan or the unfunded commitment being valued below par.
[3] All investments are LMM (as defined below) portfolio investments, unless otherwise noted. See Note C — Fair Value Hierarchy for Investments — Portfolio Composition for a description of LMM portfolio investments. All of the Company’s investments, unless otherwise noted, are encumbered either as security for the Corporate Facility or SPV Facility (each as defined below) or in support of the debentures guaranteed by the SBA (as defined below) and issued by the Funds (as defined below).
[4] All portfolio company headquarters are based in the U.S., unless otherwise noted.
[5] Investment Fair Value was determined using significant unobservable inputs, unless otherwise noted. See Note C — Fair Value Hierarchy for Investments — Portfolio Composition for further discussion. Negative fair value is the result of the capitalized discount on the loan or the unfunded commitment being valued below par.
[6] All investments are LMM portfolio investments, unless otherwise noted. See Note C — Fair Value Hierarchy for Investments — Portfolio Composition for a description of LMM portfolio investments. All of the Company’s investments, unless otherwise noted, are encumbered either as security for the Corporate Facility or SPV Facility or in support of the debentures guaranteed by the SBA and issued by the Funds.
[7] Principal is net of repayments. Cost is net of repayments and accumulated unearned income. Negative cost is the result of the capitalized discount being greater than the principal amount outstanding on the loan.
[8] Principal is net of repayments. Cost is net of repayments and accumulated unearned income. Negative cost is the result of the capitalized discount being greater than the principal amount outstanding on the loan.