Debt - Schedule of Outstanding Debt Obligations (Details) - USD ($)	Jun. 30, 2023	Apr. 17, 2023	Apr. 04, 2023	Mar. 09, 2023	Dec. 31, 2022	Jul. 26, 2022	Apr. 20, 2022	Aug. 17, 2021	Jul. 09, 2021	Jun. 11, 2021	May 05, 2021	Apr. 26, 2021	Apr. 09, 2021	Dec. 08, 2020	Nov. 20, 2020	Jul. 23, 2020	Mar. 26, 2020	Jan. 22, 2020	Oct. 08, 2019	May 28, 2019	Apr. 10, 2019
Debt Instrument [Line Items]
Total Debt	$ 8,691,275,000				$ 8,841,275,000
Outstanding Principal	7,176,450,000				7,443,419,000
Amount Available	1,469,048,000				1,353,057,000
Net Carrying Value	7,027,176,000				7,281,744,000
Unamortized debt issuance costs	85,969,000				95,647,000
Line of credit
Debt Instrument [Line Items]
Outstanding letters of credit	45,800,000				44,800,000
Line of credit | SPV Asset Facility II
Debt Instrument [Line Items]
Aggregate Principal Committed	250,000,000	$ 250,000,000			350,000,000
Outstanding Principal	140,000,000				250,000,000
Amount Available	110,000,000				100,000,000
Net Carrying Value	135,524,000				245,368,000
Unamortized debt issuance costs	4,500,000				4,600,000
Line of credit | SPV Asset Facility III
Debt Instrument [Line Items]
Aggregate Principal Committed				$ 250,000,000	250,000,000
Outstanding Principal					250,000,000
Amount Available					0
Net Carrying Value					249,372,000
Unamortized debt issuance costs					600,000
Line of credit | CLO I
Debt Instrument [Line Items]
Unamortized debt issuance costs					2,700,000
Line of credit | Revolving Credit Facility
Debt Instrument [Line Items]
Unamortized debt issuance costs	12,900,000				14,700,000
Line of credit | Revolving Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	1,795,000,000		$ 1,860,000,000		1,855,000,000
Outstanding Principal	390,175,000				557,144,000
Amount Available	1,359,048,000				1,253,057,000
Net Carrying Value	377,237,000				542,453,000
Unamortized debt issuance costs	12,900,000				14,700,000
Line of credit | Revolving Credit Facility | SPV Asset Facility II
Debt Instrument [Line Items]
Aggregate Principal Committed		$ 250,000,000
Secured debt | CLO I
Debt Instrument [Line Items]
Aggregate Principal Committed	390,000,000				390,000,000															$ 596,000,000
Outstanding Principal	390,000,000				390,000,000
Net Carrying Value	387,487,000				387,321,000
Unamortized debt issuance costs	2,500,000				2,700,000
Secured debt | CLO II
Debt Instrument [Line Items]
Aggregate Principal Committed	260,000,000				260,000,000								$ 398,100,000
Outstanding Principal	260,000,000				260,000,000
Net Carrying Value	257,347,000				257,206,000
Unamortized debt issuance costs	2,700,000				2,800,000
Secured debt | CLO III
Debt Instrument [Line Items]
Aggregate Principal Committed	260,000,000				260,000,000												$ 395,310,000
Outstanding Principal	260,000,000				260,000,000
Net Carrying Value	258,207,000				258,145,000
Unamortized debt issuance costs	1,800,000				1,900,000
Secured debt | CLO IV
Debt Instrument [Line Items]
Aggregate Principal Committed	292,500,000				292,500,000				$ 440,500,000
Outstanding Principal	292,500,000				292,500,000
Net Carrying Value	287,987,000				287,777,000
Unamortized debt issuance costs	4,500,000				4,700,000
Secured debt | CLO V
Debt Instrument [Line Items]
Aggregate Principal Committed	509,625,000				509,625,000		$ 669,200,000								$ 345,450,000
Outstanding Principal	509,625,000				509,625,000
Net Carrying Value	506,889,000				506,792,000
Unamortized debt issuance costs	2,700,000				2,800,000
Secured debt | CLO VI
Debt Instrument [Line Items]
Aggregate Principal Committed	260,000,000				260,000,000						$ 397,780,000
Outstanding Principal	260,000,000				260,000,000
Net Carrying Value	258,325,000				258,271,000
Unamortized debt issuance costs	1,700,000				1,700,000
Secured debt | CLO VII
Debt Instrument [Line Items]
Aggregate Principal Committed	239,150,000				239,150,000	$ 350,470,000
Outstanding Principal	239,150,000				239,150,000
Net Carrying Value	237,238,000				237,155,000
Unamortized debt issuance costs	1,900,000				2,000,000
Secured debt | CLO X
Debt Instrument [Line Items]
Aggregate Principal Committed	260,000,000			$ 397,700,000
Outstanding Principal	260,000,000
Net Carrying Value	258,072,000
Unamortized debt issuance costs	1,900,000
Unsecured debt investments | 2024 Notes
Debt Instrument [Line Items]
Aggregate Principal Committed	400,000,000				400,000,000																$ 400,000,000
Outstanding Principal	400,000,000				400,000,000
Net Carrying Value	388,496,000				384,851,000
Unamortized debt issuance costs	1,800,000				2,900,000
Unsecured debt investments | 2025 Notes
Debt Instrument [Line Items]
Aggregate Principal Committed	425,000,000				425,000,000														$ 425,000,000
Outstanding Principal	425,000,000				425,000,000
Net Carrying Value	422,050,000				421,242,000
Unamortized debt issuance costs	3,000,000				3,800,000
Unsecured debt investments | July 2025 Notes
Debt Instrument [Line Items]
Aggregate Principal Committed	500,000,000				500,000,000													$ 500,000,000
Outstanding Principal	500,000,000				500,000,000
Net Carrying Value	496,222,000				495,347,000
Unamortized debt issuance costs	3,800,000				4,700,000
Unsecured debt investments | 2026 Notes
Debt Instrument [Line Items]
Aggregate Principal Committed	500,000,000				500,000,000											$ 500,000,000
Outstanding Principal	500,000,000				500,000,000
Net Carrying Value	494,232,000				493,162,000
Unamortized debt issuance costs	5,800,000				6,800,000
Unsecured debt investments | July 2026 Notes
Debt Instrument [Line Items]
Aggregate Principal Committed	1,000,000,000				1,000,000,000									$ 1,000,000,000
Outstanding Principal	1,000,000,000				1,000,000,000
Net Carrying Value	985,271,000				982,993,000
Unamortized debt issuance costs	14,700,000				17,000,000
Unsecured debt investments | 2027 Notes
Debt Instrument [Line Items]
Aggregate Principal Committed	500,000,000				500,000,000							$ 500,000,000
Outstanding Principal	500,000,000				500,000,000
Net Carrying Value	439,434,000				438,332,000
Unamortized debt issuance costs	7,000,000				7,900,000
Unsecured debt investments | 2028 Notes
Debt Instrument [Line Items]
Aggregate Principal Committed	850,000,000				850,000,000			$ 400,000,000		$ 450,000,000
Outstanding Principal	850,000,000				850,000,000
Net Carrying Value	837,158,000				835,957,000
Unamortized debt issuance costs	$ 12,800,000				$ 14,000,000