FAIR VALUE MEASUREMENTS - Schedule of Investments Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2022		Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$ 1,979,877	[1]	$ 1,913,052	[2]
Level 1, 2 and 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	1,906,920		1,835,094
Level 1, 2 and 3 | First Lien Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	1,359,962		1,232,084
Level 1, 2 and 3 | Second Lien Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	262,703		341,776
Level 1, 2 and 3 | Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	94,190		77,093
Level 1, 2 and 3 | Mezzanine Loan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0		0
Level 1, 2 and 3 | Subordinated Loan and Member's Interest
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	190,065		184,141
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0		0
Level 1 | First Lien Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0		0
Level 1 | Second Lien Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0		0
Level 1 | Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0		0
Level 1 | Mezzanine Loan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0		0
Level 1 | Subordinated Loan and Member's Interest
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0		0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0		0
Level 2 | First Lien Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0		0
Level 2 | Second Lien Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0		0
Level 2 | Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0		0
Level 2 | Mezzanine Loan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0		0
Level 2 | Subordinated Loan and Member's Interest
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0		0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	1,906,920		1,835,094
Level 3 | First Lien Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	1,359,962		1,232,084
Level 3 | Second Lien Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	262,703		341,776
Level 3 | Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	94,190		77,093
Level 3 | Mezzanine Loan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0		0
Level 3 | Subordinated Loan and Member's Interest
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	190,065		184,141
Net asset value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$ 72,957		$ 77,958

[1] The Company has determined the indicated investments are non-qualifying assets under Section 55(a) of the Investment Company Act. Under the Investment Company Act, the Company may not acquire any non-qualifying assets unless, at the time such acquisition is made, qualifying assets represent at least 70% of the Company’s total assets.

[2] The Company has determined the indicated investments are non-qualifying assets under Section 55(a) of the Investment Company Act. Under the Investment Company Act, the Company may not acquire any non-qualifying assets unless, at the time such acquisition is made, qualifying assets represent at least 70% of the Company’s total assets.