FAIR VALUE MEASUREMENTS - Schedule of Reconciliation of the Beginning and Ending Balances for Investments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Total
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 1,763,604	$ 1,236,432	$ 1,598,514	$ 1,177,412
Purchase of investments	292,280	102,088	465,228	201,926
Proceeds from principal repayments and sales of investments	(96,686)	(5,697)	(142,443)	(45,245)
Payment-in-kind interest	1,529	551	3,521	872
Amortization of premium/accretion of discount, net	(1,280)	620	(291)	1,511
Transfers out of Level 3	(36,865)	(6,127)	(11,899)	(14,042)
Transfers to Level 3		9,232	9,825	17,900
Ending balance	1,911,267	1,332,959	1,911,267	1,332,959
Net change in unrealized appreciation (depreciation) on non-controlled/non-affiliated company investments still held	(12,292)	(5,030)	(13,678)	(8,755)
Total | Net realized gain (loss) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains (losses) included in earnings	977	218	(2,713)	6,699
Total | Net change in unrealized appreciation (depreciation) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains (losses) included in earnings	(12,292)	(4,358)	(8,475)	(14,074)
First Lien Term Loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1,565,397	1,074,567	1,393,011	1,016,856
Purchase of investments	280,494	85,366	452,091	163,859
Proceeds from principal repayments and sales of investments	(84,180)	(5,683)	(123,781)	(24,530)
Payment-in-kind interest	148	(15)	408	0
Amortization of premium/accretion of discount, net	(1,418)	525	(593)	1,274
Transfers out of Level 3	(36,865)	(6,127)	(11,899)	(14,042)
Transfers to Level 3		9,232	9,825	17,900
Ending balance	1,724,399	1,152,917	1,724,399	1,152,917
Net change in unrealized appreciation (depreciation) on non-controlled/non-affiliated company investments still held	(23)	(5,838)	3,368	(9,544)
First Lien Term Loans | Net realized gain (loss) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains (losses) included in earnings	846	218	(2,985)	391
First Lien Term Loans | Net change in unrealized appreciation (depreciation) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains (losses) included in earnings	(23)	(5,166)	8,322	(8,791)
Subordinated Debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	166,502	139,589	174,696	133,243
Purchase of investments	9,296	15,798	10,150	35,251
Proceeds from principal repayments and sales of investments	(12,506)	(14)	(18,589)	(12,048)
Payment-in-kind interest	1,381	566	3,113	872
Amortization of premium/accretion of discount, net	138	95	302	237
Transfers out of Level 3	0	0	0	0
Transfers to Level 3		0	0	0
Ending balance	154,692	155,148	154,692	155,148
Net change in unrealized appreciation (depreciation) on non-controlled/non-affiliated company investments still held	(10,250)	(886)	(15,501)	(2,580)
Subordinated Debt | Net realized gain (loss) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains (losses) included in earnings	131	0	272	197
Subordinated Debt | Net change in unrealized appreciation (depreciation) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains (losses) included in earnings	(10,250)	(886)	(15,252)	(2,604)
Equity Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	31,705	22,276	30,807	27,313
Purchase of investments	2,490	924	2,987	2,816
Proceeds from principal repayments and sales of investments	0	0	(73)	(8,667)
Payment-in-kind interest	0	0	0	0
Amortization of premium/accretion of discount, net	0	0	0	0
Transfers out of Level 3	0	0	0	0
Transfers to Level 3		0	0	0
Ending balance	32,176	24,894	32,176	24,894
Net change in unrealized appreciation (depreciation) on non-controlled/non-affiliated company investments still held	(2,019)	1,694	(1,545)	3,369
Equity Investments | Net realized gain (loss) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains (losses) included in earnings	0	0	0	6,111
Equity Investments | Net change in unrealized appreciation (depreciation) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains (losses) included in earnings	$ (2,019)	$ 1,694	$ (1,545)	$ (2,679)