Fair Value of Investments - Schedule of Changes in the Fair Value of Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
First-lien senior secured debt investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	$ 9,279,179	$ 9,539,774	$ 8,389,486
Purchases of investments, net	1,906,568	1,436,533	5,342,940
Payment-in-kind	127,974	98,788	38,841
Proceeds from investments, net	(2,662,751)	(1,731,097)	(4,351,523)
Net amortization/accretion of discount/premium on investments	43,588	36,044	68,015
Transfers between investment types	(47,819)
Transfers into (out of) Level 3	(487)	0	847
Fair value, end of period	8,660,754	9,279,179	9,539,774
First-lien senior secured debt investments | Net change in unrealized gain (loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net change in unrealized gain (loss) / realized gains (losses)	66,742	(100,996)	70,658
First-lien senior secured debt investments | Net realized gains (losses)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net change in unrealized gain (loss) / realized gains (losses)	(52,240)	133	(19,490)
Second-lien senior secured debt investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	1,817,286	1,921,447	1,949,703
Purchases of investments, net	0	32,091	884,294
Payment-in-kind	17,816	10,874	0
Proceeds from investments, net	(55,050)	(30,499)	(933,073)
Net amortization/accretion of discount/premium on investments	3,596	3,655	13,143
Transfers between investment types	0
Transfers into (out of) Level 3	(92,252)	(47,263)	0
Fair value, end of period	1,675,269	1,817,286	1,921,447
Second-lien senior secured debt investments | Net change in unrealized gain (loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net change in unrealized gain (loss) / realized gains (losses)	(16,127)	(73,019)	37,207
Second-lien senior secured debt investments | Net realized gains (losses)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net change in unrealized gain (loss) / realized gains (losses)	0	0	(29,827)
Unsecured debt investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	237,440	196,485	59,562
Purchases of investments, net	0	89,239	130,137
Payment-in-kind	29,044	17,947	10,253
Proceeds from investments, net	(192)	(31,506)	0
Net amortization/accretion of discount/premium on investments	476	500	335
Transfers between investment types	0
Transfers into (out of) Level 3	0	(11,620)	0
Fair value, end of period	280,958	237,440	196,485
Unsecured debt investments | Net change in unrealized gain (loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net change in unrealized gain (loss) / realized gains (losses)	14,213	(20,258)	(3,802)
Unsecured debt investments | Net realized gains (losses)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net change in unrealized gain (loss) / realized gains (losses)	(23)	(3,347)	0
Preferred equity investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	355,261	260,869	22,157
Purchases of investments, net	40,054	114,012	223,853
Payment-in-kind	33,644	18,847	10,296
Proceeds from investments, net	(6,838)	(33,694)	(136)
Net amortization/accretion of discount/premium on investments	1,087	1,412	454
Transfers between investment types	0
Transfers into (out of) Level 3	0	0	0
Fair value, end of period	433,297	355,261	260,869
Preferred equity investments | Net change in unrealized gain (loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net change in unrealized gain (loss) / realized gains (losses)	9,854	(10,667)	4,245
Preferred equity investments | Net realized gains (losses)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net change in unrealized gain (loss) / realized gains (losses)	235	4,482	0
Common equity investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	977,111	571,616	230,307
Purchases of investments, net	205,436	344,631	403,627
Payment-in-kind	718	632	529
Proceeds from investments, net	(39,400)	(50,925)	(148,551)
Net amortization/accretion of discount/premium on investments	0	0	0
Transfers between investment types	47,819
Transfers into (out of) Level 3	0	0	0
Fair value, end of period	1,207,683	977,111	571,616
Common equity investments | Net change in unrealized gain (loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net change in unrealized gain (loss) / realized gains (losses)	15,999	110,838	86,063
Common equity investments | Net realized gains (losses)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net change in unrealized gain (loss) / realized gains (losses)	0	319	(359)
Total
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	12,666,277	12,490,191	10,651,215
Purchases of investments, net	2,152,058	2,016,506	6,984,851
Payment-in-kind	209,196	147,088	59,919
Proceeds from investments, net	(2,764,231)	(1,877,721)	(5,433,283)
Net amortization/accretion of discount/premium on investments	48,747	41,611	81,947
Transfers between investment types	0
Transfers into (out of) Level 3	(92,739)	(58,883)	847
Fair value, end of period	12,257,961	12,666,277	12,490,191
Total | Net change in unrealized gain (loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net change in unrealized gain (loss) / realized gains (losses)	90,681	(94,102)	194,371
Total | Net realized gains (losses)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net change in unrealized gain (loss) / realized gains (losses)	$ (52,028)	$ 1,587	$ (49,676)