INVESTMENTS - Investment Portfolio at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	$ 1,363,048	$ 1,349,121
Senior debt and 1st lien notes
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	982,334	985,158
Subordinated debt and 2nd lien notes
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	107,913	106,894
Structured products
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	27,744	26,173
Equity shares
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	207,185	192,641
Equity warrants
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	1,147	1,043
Fair Value, Inputs, Level 1, Level 2, and Level 3
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	1,326,323	1,311,909
Level 1
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	9,981	78
Level 1 | Senior debt and 1st lien notes
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	0	0
Level 1 | Subordinated debt and 2nd lien notes
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	0	0
Level 1 | Structured products
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	0	0
Level 1 | Equity shares
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	9,936	78
Level 1 | Equity warrants
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	45	0
Level 2
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	54,689	57,380
Level 2 | Senior debt and 1st lien notes
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	36,184	36,079
Level 2 | Subordinated debt and 2nd lien notes
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	2,846	10,043
Level 2 | Structured products
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	11,943	11,258
Level 2 | Equity shares
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	3,716	0
Level 2 | Equity warrants
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	0	0
Level 3
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	1,261,653	1,254,451
Level 3 | Senior debt and 1st lien notes
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	946,150	949,079
Level 3 | Subordinated debt and 2nd lien notes
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	105,067	96,851
Level 3 | Structured products
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	15,801	14,915
Level 3 | Equity shares
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	193,533	192,563
Level 3 | Equity warrants
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	1,102	1,043
Fair Value Measured at Net Asset Value Per
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	$ 36,725	$ 37,212