Fair Value Measurements - Schedule of Reconciliation of the Beginning and Ending Balances for Investments at Fair Value that use Level 3 Inputs (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025 USD ($)	Jun. 30, 2024 USD ($) investment	Jun. 30, 2025 USD ($)	Jun. 30, 2024 USD ($) investment
Reconciliation of beginning and ending balances for investments at fair value that use Level 3 inputs
Fair value, asset, recurring basis, still held, unrealized gain (loss), statement of income or comprehensive income [extensible enumeration]	Unrealized gain (loss) of investments	Unrealized gain (loss) of investments	Unrealized gain (loss) of investments	Unrealized gain (loss) of investments
Total net change in unrealized gain (loss) on investments attributable to Level 3 investments still held	$ (9,034)	$ (9,543)	$ (10,596)	$ (3,922)
Number of investments transferred from Level 3 to Level 1 | investment		0		1
Net realized gain (loss) on investments
Fair Value Measurements
Fair value, asset, recurring basis, unobservable input reconciliation, gain (loss), statement of income or comprehensive income [extensible enumeration]	Non-controlled/non-affiliate company investments	Non-controlled/non-affiliate company investments	Non-controlled/non-affiliate company investments	Non-controlled/non-affiliate company investments
Net change in unrealized gain (loss) on investments
Fair Value Measurements
Fair value, asset, recurring basis, unobservable input reconciliation, gain (loss), statement of income or comprehensive income [extensible enumeration]	Unrealized gain (loss) of investments	Unrealized gain (loss) of investments	Unrealized gain (loss) of investments	Unrealized gain (loss) of investments
Investments
Reconciliation of beginning and ending balances for investments at fair value that use Level 3 inputs
Balance at the beginning	$ 4,520,484	$ 2,814,036	$ 4,008,824	$ 2,528,144
Purchases of investments and other adjustments to cost	849,543	704,948	1,575,486	1,073,738
Proceeds from principal payments and sales of investments	(273,244)	(129,849)	(484,607)	(220,210)
Reclassifications	0	0	0	0
Transfers in (out) of Level 3				(133)
Balance at the end	5,087,528	3,386,975	5,087,528	3,386,975
Investments | Net realized gain (loss) on investments
Reconciliation of beginning and ending balances for investments at fair value that use Level 3 inputs
Gains (losses) included in earnings	(1,758)	220	(1,640)	224
Investments | Net change in unrealized gain (loss) on investments
Reconciliation of beginning and ending balances for investments at fair value that use Level 3 inputs
Gains (losses) included in earnings	(7,497)	(2,380)	(10,535)	5,212
Senior secured loans
Reconciliation of beginning and ending balances for investments at fair value that use Level 3 inputs
Balance at the beginning	3,925,239	2,432,957	3,491,117	2,171,243
Purchases of investments and other adjustments to cost	735,543	607,868	1,341,538	948,674
Proceeds from principal payments and sales of investments	(244,817)	(123,094)	(411,296)	(198,881)
Reclassifications	(15,208)	(15,311)	(15,722)	(25,901)
Transfers in (out) of Level 3				0
Balance at the end	4,397,867	2,906,171	4,397,867	2,906,171
Senior secured loans | Net realized gain (loss) on investments
Reconciliation of beginning and ending balances for investments at fair value that use Level 3 inputs
Gains (losses) included in earnings	(2,133)	221	(1,991)	221
Senior secured loans | Net change in unrealized gain (loss) on investments
Reconciliation of beginning and ending balances for investments at fair value that use Level 3 inputs
Gains (losses) included in earnings	(757)	3,530	(5,779)	10,815
Unitranche secured loans
Reconciliation of beginning and ending balances for investments at fair value that use Level 3 inputs
Balance at the beginning	103,073	174,337	148,531	184,853
Purchases of investments and other adjustments to cost	67	1,235	410	3,673
Proceeds from principal payments and sales of investments	(262)	(6,666)	(44,810)	(20,347)
Reclassifications	0	0	0	0
Transfers in (out) of Level 3				0
Balance at the end	99,179	168,253	99,179	168,253
Unitranche secured loans | Net realized gain (loss) on investments
Reconciliation of beginning and ending balances for investments at fair value that use Level 3 inputs
Gains (losses) included in earnings	0	0	0	0
Unitranche secured loans | Net change in unrealized gain (loss) on investments
Reconciliation of beginning and ending balances for investments at fair value that use Level 3 inputs
Gains (losses) included in earnings	(3,699)	(653)	(4,952)	74
Junior secured loans
Reconciliation of beginning and ending balances for investments at fair value that use Level 3 inputs
Balance at the beginning	254,222	102,443	177,677	87,986
Purchases of investments and other adjustments to cost	16,895	47,108	96,447	62,167
Proceeds from principal payments and sales of investments	(26,622)	(73)	(26,711)	(347)
Reclassifications	15,208	12,277	13,624	8,615
Transfers in (out) of Level 3				0
Balance at the end	256,158	154,998	256,158	154,998
Junior secured loans | Net realized gain (loss) on investments
Reconciliation of beginning and ending balances for investments at fair value that use Level 3 inputs
Gains (losses) included in earnings	(59)	0	(59)	0
Junior secured loans | Net change in unrealized gain (loss) on investments
Reconciliation of beginning and ending balances for investments at fair value that use Level 3 inputs
Gains (losses) included in earnings	(3,486)	(6,757)	(4,820)	(3,423)
Equity investments
Reconciliation of beginning and ending balances for investments at fair value that use Level 3 inputs
Balance at the beginning	237,950	104,299	191,499	84,062
Purchases of investments and other adjustments to cost	97,038	48,737	137,091	59,224
Proceeds from principal payments and sales of investments	(1,543)	(16)	(1,790)	(635)
Reclassifications	0	3,034	2,098	17,286
Transfers in (out) of Level 3				(133)
Balance at the end	334,324	157,553	334,324	157,553
Equity investments | Net realized gain (loss) on investments
Reconciliation of beginning and ending balances for investments at fair value that use Level 3 inputs
Gains (losses) included in earnings	434	(1)	410	3
Equity investments | Net change in unrealized gain (loss) on investments
Reconciliation of beginning and ending balances for investments at fair value that use Level 3 inputs
Gains (losses) included in earnings	$ 445	$ 1,500	$ 5,016	$ (2,254)