Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE HIERARCHY FOR INVESTMENTS???PORTFOLIO COMPOSITION - Changes in Fair Value of Level??3 Portfolio Investments (Details)

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FAIR VALUE HIERARCHY FOR INVESTMENTS—PORTFOLIO COMPOSITION - Changes in Fair Value of Level 3 Portfolio Investments (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2023
Mar. 31, 2022
Investments    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance $ 4,100,273 $ 3,559,837
Transfers Into Level 3 Hierarchy 0 0
Redemptions/ Repayments (91,171) (201,268)
New Investments 115,134 311,755
Other 0 0
Ending balance 4,158,975 3,688,770
Investments | Net Changes from Unrealized to Realized    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Gain (loss) included in earnings 29,118 2,541
Investments | Debt and Equity Securities, Unrealized Gain (Loss) [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Gain (loss) included in earnings 5,621 15,905
Debt    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 2,928,196 2,509,568
Transfers Into Level 3 Hierarchy 0 0
Redemptions/ Repayments (88,300) (183,699)
New Investments 106,658 287,044
Other (11,446) 0
Ending balance 2,941,732 2,608,229
Debt | Net Changes from Unrealized to Realized    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Gain (loss) included in earnings 33,064 2,123
Debt | Debt and Equity Securities, Unrealized Gain (Loss) [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Gain (loss) included in earnings (26,440) (6,807)
Equity    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 1,166,643 1,043,709
Transfers Into Level 3 Hierarchy 0 0
Redemptions/ Repayments (2,871) (17,569)
New Investments 8,476 24,711
Other 14,022 0
Ending balance 1,212,214 1,073,781
Equity | Net Changes from Unrealized to Realized    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Gain (loss) included in earnings (3,946) 418
Equity | Debt and Equity Securities, Unrealized Gain (Loss) [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Gain (loss) included in earnings 29,890 22,512
Equity Warrant    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 5,434 6,560
Transfers Into Level 3 Hierarchy 0 0
Redemptions/ Repayments 0 0
New Investments 0 0
Other (2,576) 0
Ending balance 5,029 6,760
Equity Warrant | Net Changes from Unrealized to Realized    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Gain (loss) included in earnings 0 0
Equity Warrant | Debt and Equity Securities, Unrealized Gain (Loss) [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Gain (loss) included in earnings $ 2,171 $ 200