Investments - Schedule of Changes in Fair Value of Investments (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2023		Mar. 31, 2022
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		$ 2,396,036		$ 2,592,992
Net realized gains (losses)		1,770		(758)
Net change in unrealized gains (losses)		2,893		24,919
Net amortization on investments		2,496		6,431
Purchases, including capitalized PIK		175,140	[1]	220,666	[2]
Sales		(194,817)	[1]	(274,375)	[2]
Transfers into Level 3	[3]			390
Fair value, Ending balance		2,383,518		2,521,943
Net change in unrealized gains (losses) on Level 3 investments still held		(18,977)		24,638
First Lien Secured Debt | Level 3
Schedule of Investments [Line Items]
Fair value, Beginning balance		2,130,309	[4]	2,267,313	[5]
Net realized gains (losses)		2,531	[4]	(415)	[5]
Net change in unrealized gains (losses)		272	[4]	798	[5]
Net amortization on investments		2,421	[4]	6,317	[5]
Purchases, including capitalized PIK		151,510	[1],[4]	220,442	[2],[5]
Sales		(172,248)	[1],[4]	(234,949)	[2],[5]
Fair value, Ending balance		2,114,795	[4]	2,259,506	[5]
Net change in unrealized gains (losses) on Level 3 investments still held		620	[4]	1,104	[5]
Second Lien Secured Debt | Level 3
Schedule of Investments [Line Items]
Fair value, Beginning balance		70,919	[4]	105,014	[5]
Net realized gains (losses)		(1,128)	[4]	(452)	[5]
Net change in unrealized gains (losses)		21,983	[4]	2,687	[5]
Net amortization on investments		111	[4]	114	[5]
Sales		(22,528)	[1],[4]	(10,423)	[2],[5]
Fair value, Ending balance		69,357	[4]	97,844	[5]
Net change in unrealized gains (losses) on Level 3 investments still held		(235)	[4]	2,488	[5]
Unsecured Debt | Level 3
Schedule of Investments [Line Items]
Fair value, Beginning balance		50		22,000
Net realized gains (losses)				25
Net change in unrealized gains (losses)		(2)
Purchases, including capitalized PIK	[1]	1
Sales	[1]	(18)		(22,025)
Fair value, Ending balance		31
Net change in unrealized gains (losses) on Level 3 investments still held		(2)
Structured Products And Other | Level 3
Schedule of Investments [Line Items]
Fair value, Beginning balance		9,413		10,821
Net change in unrealized gains (losses)		1,383		(793)
Purchases, including capitalized PIK		106	[1]	10	[2]
Fair value, Ending balance		10,902		10,038
Net change in unrealized gains (losses) on Level 3 investments still held		1,384		(793)
Preferred Equity | Level 3
Schedule of Investments [Line Items]
Fair value, Beginning balance		35,557		28,957
Net change in unrealized gains (losses)		1,004		1,205
Purchases, including capitalized PIK	[1]	50
Fair value, Ending balance		36,611		30,162
Net change in unrealized gains (losses) on Level 3 investments still held		1,004		1,205
Common Equity/Interests | Level 3
Schedule of Investments [Line Items]
Fair value, Beginning balance		149,314		158,515
Net realized gains (losses)		367		696
Net change in unrealized gains (losses)		(21,734)		(28,543)
Net amortization on investments		(36)
Purchases, including capitalized PIK		23,473	[1]	214	[2]
Sales		(23)	[1]	(6,978)	[2]
Transfers into Level 3	[3]			390
Fair value, Ending balance		151,361		124,294
Net change in unrealized gains (losses) on Level 3 investments still held		(21,734)		(28,369)
Warrants - Warrants | Level 3
Schedule of Investments [Line Items]
Fair value, Beginning balance		474		372
Net change in unrealized gains (losses)		(13)		(273)
Fair value, Ending balance		461		99
Net change in unrealized gains (losses) on Level 3 investments still held		$ (14)		$ (273)

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

[5] Includes unfunded commitments measured at fair value of $(2,091).