v3.26.1
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2026
USD ($)
company
segment
Mar. 31, 2025
company
Mar. 31, 2026
USD ($)
company
Dec. 31, 2025
USD ($)
Schedule of Investments [Line Items]        
Cash equivalents $ 5,600   $ 5,600 $ 3,200
Cash exceeded federal deposit insurance corporation insurance protection levels 13,200   13,200 35,400
Fair value 5,674,751 [1],[2],[3]   5,674,751 [1],[2],[3] 5,518,117 [4],[5],[6]
Cost $ 4,933,484 [1],[3],[7]   4,933,484 [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) 2.70% 2.90%    
Percentage of total investment come, attributable to noncash cumulative dividend income (as a percent) 0.70% 0.50%    
Percentage of total investment income, attributable to interest income, debt investments, net (as a percent) 1.70% 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 $ 68,300   68,300 56,300
Cost $ 199,100   $ 199,100 $ 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)   1.20%   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) 4.00%     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 19 15 71  
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified (as a percent)     97.00%  
Fair value $ 3,227,400   $ 3,227,400 $ 3,057,000
Cost $ 2,577,000   $ 2,577,000 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% 20.00% 86.00%  
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 62  
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified (as a percent)     98.00%  
Fair value $ 1,993,900   $ 1,993,900 1,988,400
Cost $ 2,057,000   $ 2,057,000 $ 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) 24.00% 26.00% 84.00%  
Middle Market portfolio investments        
Schedule of Investments [Line Items]        
Percentage of portfolio investments containing limited consultation with financial advisory services firm (as a percent) 95.00%   95.00% 95.00%
Fair value $ 81,900   $ 81,900 $ 83,500
Cost $ 121,400   121,400 $ 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) 1.40%     1.50%
Middle Market portfolio investments | Investment Owned, At Cost | Investment Type Concentration Risk        
Schedule of Investments [Line Items]        
Concentration risk (as a percent) 2.50%     2.50%
Other Portfolio investments        
Schedule of Investments [Line Items]        
Fair value $ 138,500   138,500 $ 134,100
Cost $ 148,500   $ 148,500 $ 141,600
Other Portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk        
Schedule of Investments [Line Items]        
Concentration risk (as a percent) 2.40%     2.40%
Other Portfolio investments | Investment Owned, At Cost | Investment Type Concentration Risk        
Schedule of Investments [Line Items]        
Concentration risk (as a percent) 3.00%     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.