Investments - Schedule of Changes in Fair Value of Investments (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2024		Mar. 31, 2023
Schedule of Investments [Line Items]
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Unrealized Gain (Loss) on Investments		Unrealized Gain (Loss) on Investments
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Unrealized Gain (Loss) on Investments		Unrealized Gain (Loss) on Investments
Level 3
Schedule of Investments [Line Items]
Fair value, Beginning balance		$ 2,332,982		$ 2,396,036
Net realized gains (losses)		(5,832)		1,770
Net change in unrealized gains (losses)		3,771		2,893
Net amortization on investments		1,939		2,496
Purchases, including capitalized PIK		155,139	[1]	175,140	[2]
Sales		(136,868)	[1]	(194,817)	[2]
Transfers out of Level 3		(7,710)	[3]	0	[4]
Fair value, Ending balance		2,343,421		2,383,518
Net change in unrealized gains (losses) on Level 3 investments still held		(3,938)		(18,977)
First Lien Secured Debt | Level 3
Schedule of Investments [Line Items]
Fair value, Beginning balance		2,075,031	[5]	2,130,309	[6]
Net realized gains (losses)		(6,464)	[5]	2,531	[6]
Net change in unrealized gains (losses)		4,581	[5]	272	[6]
Net amortization on investments		1,933	[5]	2,421	[6]
Purchases, including capitalized PIK		154,876	[1],[5]	151,510	[2],[6]
Sales		(118,479)	[1],[5]	(172,248)	[2],[6]
Fair value, Ending balance		2,111,478	[5]	2,114,795	[6]
Net change in unrealized gains (losses) on Level 3 investments still held		(3,233)	[5]	620	[6]
Second Lien Secured Debt | Level 3
Schedule of Investments [Line Items]
Fair value, Beginning balance		31,887	[5]	70,919	[6]
Net realized gains (losses)		273	[5]	(1,128)	[6]
Net change in unrealized gains (losses)		12,296	[5]	21,983	[6]
Net amortization on investments		6	[5]	111	[6]
Purchases, including capitalized PIK	[1],[5]	146
Sales		(31,339)	[1],[5]	(22,528)	[2],[6]
Transfers out of Level 3		(7,710)	[3],[5]	0	[4],[6]
Fair value, Ending balance		5,559	[5]	69,357	[6]
Net change in unrealized gains (losses) on Level 3 investments still held		(594)	[5]	(235)	[6]
Unsecured Debt | Level 3
Schedule of Investments [Line Items]
Net change in unrealized gains (losses)		(2,335)		(2)
Purchases, including capitalized PIK	[2]			1
Sales		2,664		(18)	[2]
Fair value, Ending balance		329		(31)
Net change in unrealized gains (losses) on Level 3 investments still held		(2,335)		(2)
Structured Products And Other | Level 3
Schedule of Investments [Line Items]
Fair value, Beginning balance		41,333		9,413
Net change in unrealized gains (losses)		(3,347)		1,383
Purchases, including capitalized PIK		0	[1]	106	[2]
Sales	[1]	(2,347)
Fair value, Ending balance		35,639		10,902
Net change in unrealized gains (losses) on Level 3 investments still held		(3,346)		1,384
Preferred Equity | Level 3
Schedule of Investments [Line Items]
Fair value, Beginning balance		32,405		35,557
Net change in unrealized gains (losses)		231		1,004
Purchases, including capitalized PIK		116	[1]	50	[2]
Fair value, Ending balance		32,752		36,611
Net change in unrealized gains (losses) on Level 3 investments still held		231		1,004
Common Equity/Interests | Level 3
Schedule of Investments [Line Items]
Fair value, Beginning balance		152,127		149,314
Net realized gains (losses)		359		367
Net change in unrealized gains (losses)		(7,138)		(21,734)
Net amortization on investments				(36)
Purchases, including capitalized PIK		1	[1]	23,473	[2]
Sales		12,057	[1]	(23)	[2]
Fair value, Ending balance		157,406		151,361
Net change in unrealized gains (losses) on Level 3 investments still held		5,856		(21,734)
Warrants - Warrants | Level 3
Schedule of Investments [Line Items]
Fair value, Beginning balance		199		474
Net change in unrealized gains (losses)		(517)		(13)
Sales		576	[1]	0	[2]
Fair value, Ending balance		258		461
Net change in unrealized gains (losses) on Level 3 investments still held		$ (517)		$ (14)

[1] Includes reorganizations and restructuring of investments.

[2] Includes reorganizations and restructuring of investments.

[3] Transfers out (if any) of Level 3 are due to an increase in the quantity and reliability of broker quotes obtained and transfers into (if any) Level 3 are due to a decrease in the quantity and reliability of broker quotes obtained as assessed by the Investment Adviser. Transfers are assumed to have occurred at the end of the period. There were no transfers between Level 1 and Level 2 fair value measurements during the period shown.

[4] Transfers out (if any) of Level 3 are due to an increase in the quantity and reliability of broker quotes obtained and transfers into (if any) Level 3 are due to a decrease in the quantity and reliability of broker quotes obtained as assessed by the Investment Adviser. Transfers are assumed to have occurred at the end of the period. There were no transfers between Level 1 and Level 2 fair value measurements during the period shown.

[5] Includes unfunded commitments measured at fair value of $(3,976).

[6] Includes unfunded commitments measured at fair value of $(4,006).