FAIR VALUE HIERARCHY FOR INVESTMENTS—PORTFOLIO COMPOSITION - Schedule of Changes in Fair Value of Level 3 Portfolio Investments (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2025	Jun. 30, 2024
Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 4,932,669	$ 4,286,271
Transfers Out of Level 3 Hierarchy	(16,810)
Transfers Into Level 3 Hierarchy		0
Redemptions/ Repayments	(544,895)	(434,678)
New Investments	655,742	822,792
Other	0	0
Ending balance	5,071,513	4,737,511
Investments \| Net Changes from Unrealized to Realized
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	(26,770)	6,508
Investments \| Net Unrealized Appreciation (Depreciation)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	71,577	56,618
Debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	3,278,365	2,883,917
Transfers Out of Level 3 Hierarchy	0
Transfers Into Level 3 Hierarchy		0
Redemptions/ Repayments	(514,216)	(406,233)
New Investments	575,433	753,750
Other	(30,773)	18,859
Ending balance	3,327,412	3,238,599
Debt \| Net Changes from Unrealized to Realized
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	38,415	7,468
Debt \| Net Unrealized Appreciation (Depreciation)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	(19,812)	(19,162)
Equity
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1,637,181	1,395,744
Transfers Out of Level 3 Hierarchy	(16,810)
Transfers Into Level 3 Hierarchy		0
Redemptions/ Repayments	(30,679)	(28,445)
New Investments	80,309	65,122
Other	30,773	(18,859)
Ending balance	1,719,038	1,487,993
Equity \| Net Changes from Unrealized to Realized
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	(65,185)	(960)
Equity \| Net Unrealized Appreciation (Depreciation)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	83,449	75,391
Equity Warrant
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	17,123	6,610
Transfers Out of Level 3 Hierarchy	0
Transfers Into Level 3 Hierarchy		0
Redemptions/ Repayments	0	0
New Investments	0	3,920
Other	0	0
Ending balance	25,063	10,919
Equity Warrant \| Net Changes from Unrealized to Realized
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	0	0
Equity Warrant \| Net Unrealized Appreciation (Depreciation)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	$ 7,940	$ 389

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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 settlement 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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