Debt - Schedule of Debt Obligations (Details) - USD ($)	Dec. 31, 2023	Dec. 04, 2023	Nov. 17, 2023	Apr. 17, 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	$ 8,677,882,000					$ 8,841,275,000
Outstanding Principal	7,201,927,000					7,443,419,000
Amount Available	1,416,815,000					1,353,057,000
Net Carrying Value	7,077,088,000					7,281,744,000
Unamortized debt issuance costs	81,492,000					95,647,000
Line of credit
Debt Instrument [Line Items]
Outstanding letters of credit	59,100,000					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	250,000,000					250,000,000
Amount Available	0					100,000,000
Net Carrying Value	245,728,000					245,368,000
Unamortized debt issuance costs	4,300,000					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	18,000,000					14,700,000
Line of credit | Revolving Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	1,895,000,000	$ 1,900,000,000	$ 1,850,000,000			1,855,000,000
Outstanding Principal	419,045,000					557,144,000
Amount Available	1,416,815,000					1,253,057,000
Net Carrying Value	401,075,000					542,453,000
Unamortized debt issuance costs	18,000,000					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	276,607,000					390,000,000															$ 596,000,000
Outstanding Principal	276,607,000					390,000,000
Net Carrying Value	274,213,000					387,321,000
Unamortized debt issuance costs	2,400,000					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	257,467,000					257,206,000
Unamortized debt issuance costs	2,500,000					2,800,000
Secured debt | CLO III
Debt Instrument [Line Items]
Aggregate Principal Committed	260,000,000					260,000,000												$ 395,300,000
Outstanding Principal	260,000,000					260,000,000
Net Carrying Value	258,324,000					258,145,000
Unamortized debt issuance costs	1,700,000					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	288,184,000					287,777,000
Unamortized debt issuance costs	4,300,000					4,700,000
Secured debt | CLO V
Debt Instrument [Line Items]
Aggregate Principal Committed	509,625,000					509,625,000		$ 669,200,000								$ 345,500,000
Outstanding Principal	509,625,000					509,625,000
Net Carrying Value	507,000,000					506,792,000
Unamortized debt issuance costs	2,600,000					2,800,000
Secured debt | CLO VI
Debt Instrument [Line Items]
Aggregate Principal Committed	260,000,000					260,000,000						$ 397,800,000
Outstanding Principal	260,000,000					260,000,000
Net Carrying Value	258,425,000					258,271,000
Unamortized debt issuance costs	1,600,000					1,700,000
Secured debt | CLO VII
Debt Instrument [Line Items]
Aggregate Principal Committed	239,150,000					239,150,000	$ 350,500,000
Outstanding Principal	239,150,000					239,150,000
Net Carrying Value	237,288,000					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	258,126,000
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	395,942,000					384,851,000
Unamortized debt issuance costs	600,000					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	422,880,000					421,242,000
Unamortized debt issuance costs	2,100,000					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	497,118,000					495,347,000
Unamortized debt issuance costs	2,900,000					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	495,320,000					493,162,000
Unamortized debt issuance costs	4,700,000					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	987,597,000					982,993,000
Unamortized debt issuance costs	12,400,000					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	454,017,000					438,332,000
Unamortized debt issuance costs	6,000,000					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	838,384,000					835,957,000
Unamortized debt issuance costs	$ 11,600,000					$ 14,000,000