INVESTMENTS - Superscript (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2022	Dec. 31, 2021
Schedule of Investments [Line Items]
STRS JV's portfolio company investments as a percentage of members' equity	222.86%	234.24%
STRS JV's portfolio company investments as a percentage of total assets	92.00%	95.00%
PIK interest rate		1.50%
One-month LIBOR		0.10%
Three-month LIBOR		0.21%
Six-month LIBOR		0.34%
One-month GBP LIBOR		0.19%
Three-month GBP LIBOR		0.26%
Six-month GBP LIBOR		0.47%
Three-month Euro EurIBOR		(0.57%)
CDOR		0.52%
Prime		3.25%
STRS JV
Schedule of Investments [Line Items]
STRS JV's portfolio company investments as a percentage of members' equity	849.00%	998.00%
PIK interest rate		7.00%
Outstanding commitments to fund investments	$ 28,762	$ 22,883
Investments on non-accrual	$ 0	$ 0