v3.26.1
FAIR VALUE MEASUREMENTS - Schedule of Reconciliation of the Beginning and Ending Balances for Investments (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Total        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning balance $ 1,949,796 $ 2,041,705 $ 1,935,882 $ 1,994,227
Purchase of investments and other adjustments to cost 22,755 83,896 107,113 235,915
Proceeds from principal repayments and sales of investments (67,449) (142,011) (132,215) (252,139)
Payment-in-kind interest 2,274 2,264 5,396 4,629
Amortization of premium/accretion of discount, net 759 1,023 1,797 2,600
Transfers out of Level 3 (5,133) (5,102) (2,490) (1,653)
Transfers to level 3 0 11,776 0 22,148
Ending balance 1,885,317 1,986,257 1,885,317 1,986,257
Net change in unrealized appreciation (depreciation) on non-controlled/non-affiliated company investments still held (6,459) (6,662) (20,877) (12,416)
First-Lien Debt        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning balance 1,766,514 1,853,071 1,748,505 1,806,850
Purchase of investments and other adjustments to cost 18,129 78,636 89,867 223,580
Proceeds from principal repayments and sales of investments (56,131) (137,788) (105,648) (242,424)
Payment-in-kind interest 755 436 1,688 861
Amortization of premium/accretion of discount, net 677 900 1,618 2,294
Transfers out of Level 3 (5,133) (2,538) (2,490) 0
Transfers to level 3 0 3,082 0 13,790
Ending balance 1,709,082 1,790,722 1,709,082 1,790,722
Net change in unrealized appreciation (depreciation) on non-controlled/non-affiliated company investments still held (16,081) (4,449) (25,267) (6,959)
Subordinated Debt        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning balance 141,910 153,517 155,198 150,779
Purchase of investments and other adjustments to cost 1,828 2,392 5,088 9,451
Proceeds from principal repayments and sales of investments (11,318) (4,223) (26,455) (9,463)
Payment-in-kind interest 1,519 1,828 3,708 3,768
Amortization of premium/accretion of discount, net 82 123 179 306
Transfers out of Level 3 0 0 0 0
Transfers to level 3 0 8,694 0 8,358
Ending balance 133,405 160,006 133,405 160,006
Net change in unrealized appreciation (depreciation) on non-controlled/non-affiliated company investments still held 10,962 (2,321) 5,819 (3,260)
Equity Investments        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning balance 41,372 35,117 32,179 36,598
Purchase of investments and other adjustments to cost 2,798 2,868 12,158 2,884
Proceeds from principal repayments and sales of investments 0 0 (112) (252)
Payment-in-kind interest 0 0 0 0
Amortization of premium/accretion of discount, net 0 0 0 0
Transfers out of Level 3 0 (2,564) 0 (1,653)
Transfers to level 3 0 0 0 0
Ending balance 42,830 35,529 42,830 35,529
Net change in unrealized appreciation (depreciation) on non-controlled/non-affiliated company investments still held (1,340) 108 (1,429) (2,197)
Income Statement Location [Axis]: us-gaap:DebtAndEquitySecuritiesRealizedGainLoss | Total        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Total gains (losses) included in earnings (11,260) (10,771) (14,548) (9,684)
Income Statement Location [Axis]: us-gaap:DebtAndEquitySecuritiesRealizedGainLoss | First-Lien Debt        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Total gains (losses) included in earnings 405 (10,821) (3,117) (9,938)
Income Statement Location [Axis]: us-gaap:DebtAndEquitySecuritiesRealizedGainLoss | Subordinated Debt        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Total gains (losses) included in earnings (11,665) 50 (11,465) 105
Income Statement Location [Axis]: us-gaap:DebtAndEquitySecuritiesRealizedGainLoss | Equity Investments        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Total gains (losses) included in earnings 0 0 34 149
Income Statement Location [Axis]: us-gaap:UnrealizedGainLossInvestmentDerivativeAndForeignCurrencyTransactionOperatingAfterTax | Total        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Total gains (losses) included in earnings (6,425) 3,477 (15,618) (9,786)
Income Statement Location [Axis]: us-gaap:UnrealizedGainLossInvestmentDerivativeAndForeignCurrencyTransactionOperatingAfterTax | First-Lien Debt        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Total gains (losses) included in earnings (16,134) 5,744 (21,341) (4,291)
Income Statement Location [Axis]: us-gaap:UnrealizedGainLossInvestmentDerivativeAndForeignCurrencyTransactionOperatingAfterTax | Subordinated Debt        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Total gains (losses) included in earnings 11,049 (2,375) 7,152 (3,298)
Income Statement Location [Axis]: us-gaap:UnrealizedGainLossInvestmentDerivativeAndForeignCurrencyTransactionOperatingAfterTax | Equity Investments        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Total gains (losses) included in earnings $ (1,340) $ 108 $ (1,429) $ (2,197)