INVESTMENTS - Schedule of Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Investments
Investments, amortized cost	$ 773,406	$ 831,960
Investments	764,554	819,208
First lien secured loans
Investments
Investments, amortized cost	622,517	709,318
Investments	615,945	697,232
Second lien secured loans
Investments
Investments, amortized cost	24,529	25,484
Investments	20,383	23,650
Subordinated Notes
Investments
Investments, amortized cost	167	167
Investments	167	167
Subordinated Note to STRS JV
Investments
Investments, amortized cost	80,000	60,000
Investments	80,000	60,000
Equity (excluding STRS JV)
Investments
Investments, amortized cost	26,193	21,991
Investments	25,993	22,552
Equity in STRS JV
Investments
Investments, amortized cost	20,000	15,000
Investments	$ 22,066	$ 15,607