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Fair Value - Level III Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Total
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 3,184,377	$ 3,046,993	$ 3,136,291	$ 2,843,456
Purchases, including capitalized PIK and revolver fundings	51,977	266,387	182,910	440,759
Proceeds from sales and paydowns of investments	(141,689)	(206,787)	(232,298)	(301,728)
Transfers into Level III	16,164	109,609	15,726	158,899
Transfers out of Level III	(11,136)	(75,436)	(11,490)	(10,000)
Ending balance	3,095,531	3,129,485	3,095,531	3,129,485
Unrealized (depreciation) appreciation for the period relating to those Level III assets that were still held by the Company at the end of the period:	(11,932)	(1,298)	(3,100)	1,878
Total | Net realized gains (losses) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings	2,565	16,518	3,273	35,690
Total | Net change in unrealized appreciation (depreciation)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings	(6,727)	(27,799)	1,119	(37,591)
First lien
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1,798,746	1,711,500	1,753,967	1,635,143
Purchases, including capitalized PIK and revolver fundings	40,201	243,696	158,106	399,092
Proceeds from sales and paydowns of investments	(131,359)	(150,322)	(202,592)	(203,478)
Transfers into Level III	0	27,749	0	0
Transfers out of Level III	(11,136)	0	(11,490)	0
Ending balance	1,693,215	1,835,954	1,693,215	1,835,954
Unrealized (depreciation) appreciation for the period relating to those Level III assets that were still held by the Company at the end of the period:	(3,604)	3,991	7,374	3,775
First lien | Net realized gains (losses) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings	(92)	(595)	(14,048)	(664)
First lien | Net change in unrealized appreciation (depreciation)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings	(3,145)	3,926	9,272	5,861
Second lien
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	480,398	446,914	480,068	319,120
Purchases, including capitalized PIK and revolver fundings	997	2,495	1,942	11,846
Proceeds from sales and paydowns of investments	(190)	(6,722)	(190)	(14,500)
Transfers into Level III	16,164	81,860	15,726	158,899
Transfers out of Level III	0	(75,436)	0	(10,000)
Ending balance	495,695	434,069	495,695	434,069
Unrealized (depreciation) appreciation for the period relating to those Level III assets that were still held by the Company at the end of the period:	803	(15,042)	7,654	(31,296)
Second lien | Net realized gains (losses) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings	(7,223)	0	(11,934)	0
Second lien | Net change in unrealized appreciation (depreciation)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings	5,549	(15,042)	10,083	(31,296)
Subordinated
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	74,348	54,867	72,842	50,742
Purchases, including capitalized PIK and revolver fundings	4,807	1,244	6,577	6,777
Proceeds from sales and paydowns of investments	0	0	0	0
Transfers into Level III	0	0	0	0
Transfers out of Level III	0	0	0	0
Ending balance	78,960	55,968	78,960	55,968
Unrealized (depreciation) appreciation for the period relating to those Level III assets that were still held by the Company at the end of the period:	(195)	(144)	(352)	(1,551)
Subordinated | Net realized gains (losses) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings	0	0	0	0
Subordinated | Net change in unrealized appreciation (depreciation)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings	(195)	(143)	(459)	(1,551)
Equity and other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	830,885	833,712	829,414	838,451
Purchases, including capitalized PIK and revolver fundings	5,972	18,952	16,285	23,044
Proceeds from sales and paydowns of investments	(10,140)	(49,743)	(29,516)	(83,750)
Transfers into Level III	0	0	0	0
Transfers out of Level III	0	0	0	0
Ending balance	827,661	803,494	827,661	803,494
Unrealized (depreciation) appreciation for the period relating to those Level III assets that were still held by the Company at the end of the period:	(8,936)	9,897	(17,776)	30,950
Equity and other | Net realized gains (losses) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings	9,880	17,113	29,255	36,354
Equity and other | Net change in unrealized appreciation (depreciation)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in earnings	$ (8,936)	$ (16,540)	$ (17,777)	$ (10,605)

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Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales and Settlements

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Amount of unrealized gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3) and still held.

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Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

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