Fair Value of Financial Instruments - Changes in Fair Value of Investments Using Level 3 Inputs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	$ 2,993,521	$ 2,484,558	$ 2,693,938	$ 2,434,638
Purchases or originations	177,820	252,149	631,994	663,601
Repayments / redemptions	(142,133)	(21,559)	(318,526)	(383,438)
Sale Proceeds	(5,380)		(11,188)	(18,315)
Paid-in-kind interest	5,033	2,861	11,667	9,623
Net change in unrealized gains (losses)	$ 3,737	$ (11,717)	$ 11,917	$ (66,031)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net Change In Unrealized Gains Losses On Investments And Foreign Currency Translation	Net Change In Unrealized Gains Losses On Investments And Foreign Currency Translation	Net Change In Unrealized Gains Losses On Investments And Foreign Currency Translation	Net Change In Unrealized Gains Losses On Investments And Foreign Currency Translation
Net realized gains (losses)	$ 3,193	$ 55	$ 8,240	$ 14,190
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net Realized Gains Losses on Investments and Foreign Currency Translation	Net Realized Gains Losses on Investments and Foreign Currency Translation	Net Realized Gains Losses on Investments and Foreign Currency Translation	Net Realized Gains Losses on Investments and Foreign Currency Translation
Net amortization of discount on securities	$ 4,825	$ 3,347	$ 11,843	$ 12,697
Transfers into (out of) Level 3			731	42,729
Balance, End of Period	3,040,616	2,709,694	3,040,616	2,709,694
First-lien Debt Investments
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	2,777,390	2,295,057	2,495,959	2,298,856
Purchases or originations	176,758	243,794	594,216	622,416
Repayments / redemptions	(142,031)	(21,559)	(318,424)	(383,428)
Paid-in-kind interest	3,830	2,796	10,127	9,433
Net change in unrealized gains (losses)	10,480	(7,332)	37,626	(43,946)
Net realized gains (losses)	(173)	55	(198)	168
Net amortization of discount on securities	4,792	3,328	11,740	12,640
Balance, End of Period	2,831,046	2,516,139	2,831,046	2,516,139
Second-lien Debt Investments
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	39,708	41,523	40,762
Purchases or originations			4,850	54
Repayments / redemptions				(10)
Paid-in-kind interest	207		401
Net change in unrealized gains (losses)	1	(344)	(6,140)	(1,629)
Net amortization of discount on securities	24	18	67	53
Transfers into (out of) Level 3				42,729
Balance, End of Period	39,940	41,197	39,940	41,197
Mezzanine Debt Investments
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	40,237	10,397	10,158	18,549
Purchases or originations			29,806
Repayments / redemptions	(102)		(102)
Paid-in-kind interest	996	65	1,139	190
Net change in unrealized gains (losses)	(2,373)	(494)	(2,270)	(6,640)
Net amortization of discount on securities	9	1	36	4
Transfers within Level 3	(2,500)		(2,500)	(2,134)
Balance, End of Period	36,267	9,969	36,267	9,969
Equity and Other Investments
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	136,186	137,581	147,059	117,233
Purchases or originations	1,062	8,355	3,122	41,131
Sale Proceeds	(5,380)		(11,188)	(18,315)
Net change in unrealized gains (losses)	(4,371)	(3,547)	(17,299)	(13,816)
Net realized gains (losses)	3,366		8,438	14,022
Transfers within Level 3	2,500		2,500	2,134
Transfers into (out of) Level 3			731
Balance, End of Period	$ 133,363	$ 142,389	$ 133,363	$ 142,389