INVESTMENTS - Investment Portfolio at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	$ 3,430,001	$ 3,094,065
Senior debt and 1st lien notes
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	2,821,555	2,503,156
Subordinated debt and 2nd lien notes
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	125,707	122,748
Structured products
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	84,460	80,401
Equity shares
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	355,740	337,684
Equity warrants
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	2,880	2,813
Royalty rights
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	15,946	14,583
Short-term investments
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	10,200	10,200
Level 1
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	10,200	10,200
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	0	0
Level 1 | Equity warrants
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	0	0
Level 1 | Royalty rights
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	0	0
Level 1 | Short-term investments
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	10,200	10,200
Level 2
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	177,701	173,320
Level 2 | Senior debt and 1st lien notes
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	99,744	100,979
Level 2 | Subordinated debt and 2nd lien notes
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	18,092	11,839
Level 2 | Structured products
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	59,865	60,502
Level 2 | Equity shares
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	0	0
Level 2 | Equity warrants
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	0	0
Level 2 | Royalty rights
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	0	0
Level 2 | Short-term investments
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	3,228,587	2,888,065
Level 3 | Senior debt and 1st lien notes
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	2,721,811	2,402,177
Level 3 | Subordinated debt and 2nd lien notes
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	107,615	110,909
Level 3 | Structured products
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	24,595	19,899
Level 3 | Equity shares
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	355,740	337,684
Level 3 | Equity warrants
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	2,880	2,813
Level 3 | Royalty rights
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	15,946	14,583
Level 3 | Short-term investments
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	0	0
Investments subject to leveling
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	3,416,488	3,071,585
Investments in joint ventures
Schedule of Equity Method Investments [Line Items]
Total investments at fair value	$ 13,513	$ 22,480