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Fair Value Measurements - Summary of Changes in Fair Value of Investments Measured Using Level 3 Inputs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Total Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	$ 10,330,365	$ 9,426,489	$ 9,710,582	$ 9,472,796
Purchases of investments	739,127	114,640
Proceeds from principal repayments and sales of investments	(186,370)	(71,040)
Accretion of discount/(amortization of premium)	9,375	8,443
Transfers into Level 3	50,239	4,938
Transfers out of Level 3	0	(91,939)
Fair value, end of period	10,330,365	9,426,489
Net change in unrealized appreciation (depreciation) included in earnings related to financial instruments, included in net unrealized appreciation (depreciation) on the consolidated statements of operations	7,674	(11,395)
Investments, Realized Gain (Loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net realized gain (loss)	428	46
Investments, Unrealized Gain (Loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net realized gain (loss)	6,984	(11,395)
First lien debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	10,178,311	9,225,290	9,564,203	9,275,511
Purchases of investments	734,974	114,229
Proceeds from principal repayments and sales of investments	(186,370)	(71,040)
Accretion of discount/(amortization of premium)	9,341	8,407
Transfers into Level 3	50,239	4,938
Transfers out of Level 3	0	(91,939)
Fair value, end of period	10,178,311	9,225,290
Net change in unrealized appreciation (depreciation) included in earnings related to financial instruments, included in net unrealized appreciation (depreciation) on the consolidated statements of operations	6,191	(14,862)
Debt Securities, First Lien, Realized Gain (Loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net realized gain (loss)	428	46
Debt Securities, First Lien, Unrealized Gain (Loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net realized gain (loss)	5,496	(14,862)
Second lien debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	41,515	46,678	41,515	46,336
Purchases of investments	180	411
Proceeds from principal repayments and sales of investments	0	0
Accretion of discount/(amortization of premium)	25	36
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair value, end of period	41,515	46,678
Net change in unrealized appreciation (depreciation) included in earnings related to financial instruments, included in net unrealized appreciation (depreciation) on the consolidated statements of operations	(205)	(105)
Debt Securities, Second Lien, Realized Gain (Loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net realized gain (loss)	0	0
Debt Securities, Second Lien, Unrealized Gain (Loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net realized gain (loss)	(205)	(105)
Unsecured debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	11,859		9,924
Purchases of investments	1,785
Proceeds from principal repayments and sales of investments	0
Accretion of discount/(amortization of premium)	9
Transfers into Level 3	0
Transfers out of Level 3	0
Fair value, end of period	11,859
Net change in unrealized appreciation (depreciation) included in earnings related to financial instruments, included in net unrealized appreciation (depreciation) on the consolidated statements of operations	135
Unsecured Debt, Realized Gain (Loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net realized gain (loss)	0
Unsecured Debt, Unrealized Gain (Loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net realized gain (loss)	141
Investments in equity
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	98,680	154,521	$ 94,940	$ 150,949
Purchases of investments	2,188	0
Proceeds from principal repayments and sales of investments	0	0
Accretion of discount/(amortization of premium)	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair value, end of period	98,680	154,521
Net change in unrealized appreciation (depreciation) included in earnings related to financial instruments, included in net unrealized appreciation (depreciation) on the consolidated statements of operations	1,553	3,572
Equity Securities, Realized Gain (Loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net realized gain (loss)	0	0
Equity Securities, Unrealized Gain (Loss)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net realized gain (loss)	$ 1,552	$ 3,572

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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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Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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