INVESTMENTS - Portfolio by Industry Grouping (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Investments, fair value	$ 642,213	$ 696,168
Percent of net assets	224.40%	219.70%
Advertising
Investments, fair value	$ 12,035	$ 12,040
Air Freight & Logistics
Investments, fair value	3,311	3,504
Broadline Retail
Investments, fair value	17,827	18,759
Building Products
Investments, fair value	13,437	13,313
Construction & Engineering
Investments, fair value	16,253	9,550
Data Processing & Outsourced Services
Investments, fair value	12,885	14,659
Distributors
Investments, fair value	9,372
Diversified Support Services
Investments, fair value	19,282	19,136
Environmental & Facilities Services
Investments, fair value	29,963	19,691
Food Distributors
Investments, fair value	4,993
Health Care Facilities
Investments, fair value	8,004
Health Care Services
Investments, fair value	4,995	5,022
Health Care Supplies
Investments, fair value	7,696	7,530
Household Appliances
Investments, fair value	7,632	8,168
Industrial Machinery & Supplies & Components
Investments, fair value		6,561
Investment Banking & Brokerage
Investments, fair value		4,977
Packaged Foods & Meats
Investments, fair value	7,009	6,904
Research & Consulting Services
Investments, fair value	11,977	16,149
Technology Hardware, Storage & Peripherals
Investments, fair value	17,949	18,853
Paper & Plastic Packaging Products & Materials
Investments, fair value	14,881	14,913
Wireless Telecommunication Services
Investments, fair value	6,332	6,295
Investments Excluding STRS JV's
Investments, fair value	$ 535,056	$ 588,970
Percent of net assets	100.00%	100.00%
Investments Excluding STRS JV's \| Advertising
Investments, fair value	$ 17,451	$ 420
Percent of net assets	3.30%	0.10%
Investments Excluding STRS JV's \| Air Freight & Logistics
Investments, fair value	$ 28,518	$ 22,616
Percent of net assets	5.30%	3.80%
Investments Excluding STRS JV's \| Application Software
Investments, fair value	$ 26,924	$ 34,202
Percent of net assets	5.00%	5.80%
Investments Excluding STRS JV's \| Automotive Retail
Investments, fair value		$ 12,407
Percent of net assets		2.10%
Investments Excluding STRS JV's \| Broadcasting
Investments, fair value	$ 7,833	$ 7,243
Percent of net assets	1.50%	1.20%
Investments Excluding STRS JV's \| Broadline Retail
Investments, fair value	$ 5,336	$ 19,911
Percent of net assets	1.00%	3.40%
Investments Excluding STRS JV's \| Building Products
Investments, fair value	$ 13,206	$ 15,863
Percent of net assets	2.50%	2.70%
Investments Excluding STRS JV's \| Commodity Chemicals
Investments, fair value	$ 16,026	$ 30,712
Percent of net assets	3.00%	5.20%
Investments Excluding STRS JV's \| Construction & Engineering
Investments, fair value	$ 3,927	$ 541
Percent of net assets	0.70%	0.10%
Investments Excluding STRS JV's \| Construction Materials
Investments, fair value	$ 5,640	$ 6,901
Percent of net assets	1.10%	1.20%
Investments Excluding STRS JV's \| Data Processing & Outsourced Services
Investments, fair value	$ 28,572	$ 33,997
Percent of net assets	5.30%	5.80%
Investments Excluding STRS JV's \| Distributors
Investments, fair value	$ 10,690	$ 12,475
Percent of net assets	2.00%	2.10%
Investments Excluding STRS JV's \| Diversified Chemicals
Investments, fair value	$ 4,999	$ 10,259
Percent of net assets	0.90%	1.70%
Investments Excluding STRS JV's \| Diversified Financial Services
Investments, fair value		$ 3,472
Percent of net assets		0.60%
Investments Excluding STRS JV's \| Diversified Support Services
Investments, fair value	$ 9,563	$ 9,598
Percent of net assets	1.80%	1.60%
Investments Excluding STRS JV's \| Education Services
Investments, fair value	$ 21,314	$ 20,318
Percent of net assets	4.00%	3.50%
Investments Excluding STRS JV's \| Electric Utilities
Investments, fair value	$ 16,032	$ 15,954
Percent of net assets	3.00%	2.70%
Investments Excluding STRS JV's \| Environmental & Facilities Services
Investments, fair value	$ 1,400	$ 23,878
Percent of net assets	0.30%	4.10%
Investments Excluding STRS JV's \| Food Distributors
Investments, fair value	$ 350
Percent of net assets	0.10%
Investments Excluding STRS JV's \| Health Care Facilities
Investments, fair value	$ 8,660	$ 8,966
Percent of net assets	1.60%	1.50%
Investments Excluding STRS JV's \| Health Care Services
Investments, fair value	$ 19,589	$ 17,643
Percent of net assets	3.70%	3.00%
Investments Excluding STRS JV's \| Health Care Supplies
Investments, fair value	$ 19,535	$ 18,983
Percent of net assets	3.70%	3.20%
Investments Excluding STRS JV's \| Heavy Electrical Equipment
Investments, fair value	$ 10,138	$ 10,135
Percent of net assets	1.90%	1.70%
Investments Excluding STRS JV's \| Home Furnishings
Investments, fair value	$ 25,376	$ 27,508
Percent of net assets	4.70%	4.70%
Investments Excluding STRS JV's \| Household Appliances
Investments, fair value	$ 22,162	$ 22,727
Percent of net assets	4.10%	3.90%
Investments Excluding STRS JV's \| Household Products
Investments, fair value	$ 11,656	$ 10,873
Percent of net assets	2.20%	1.90%
Investments Excluding STRS JV's \| Industrial Machinery & Supplies & Components
Investments, fair value	$ 13,237	$ 6,417
Percent of net assets	2.50%	1.20%
Investments Excluding STRS JV's \| Integrated Telecommunication Services
Investments, fair value	$ 13,135	$ 13,191
Percent of net assets	2.50%	2.20%
Investments Excluding STRS JV's \| Interactive Media & Services
Investments, fair value	$ 15,970	$ 1,615
Percent of net assets	3.00%	0.30%
Investments Excluding STRS JV's \| Investment Banking & Brokerage
Investments, fair value		$ 3,522
Percent of net assets		0.60%
Investments Excluding STRS JV's \| IT Consulting & Other Services
Investments, fair value	$ 3,504	$ 6,549
Percent of net assets	0.60%	1.10%
Investments Excluding STRS JV's \| Leisure Facilities
Investments, fair value	$ 19,580	$ 22,619
Percent of net assets	3.70%	3.80%
Investments Excluding STRS JV's \| Leisure Products
Investments, fair value	$ 23,298	$ 18,488
Percent of net assets	4.40%	3.10%
Investments Excluding STRS JV's \| Life Sciences Tools & Services
Investments, fair value	$ 5,000	$ 4,901
Percent of net assets	0.90%	0.80%
Investments Excluding STRS JV's \| Office Services & Supplies
Investments, fair value		$ 15,503
Percent of net assets		2.60%
Investments Excluding STRS JV's \| Packaged Foods & Meats
Investments, fair value	$ 4,087
Percent of net assets	0.70%
Investments Excluding STRS JV's \| Paper Products
Investments, fair value	$ 9,453
Percent of net assets	1.80%
Investments Excluding STRS JV's \| Real Estate Services
Investments, fair value	$ 20,872	$ 22,758
Percent of net assets	3.90%	3.90%
Investments Excluding STRS JV's \| Research & Consulting Services
Investments, fair value	$ 5,295	$ 8,438
Percent of net assets	0.90%	1.40%
Investments Excluding STRS JV's \| Security & Alarm Services
Investments, fair value	$ 7,070
Percent of net assets	1.30%
Investments Excluding STRS JV's \| Specialized Consumer Services
Investments, fair value	$ 7,122	$ 17,951
Percent of net assets	1.30%	3.00%
Investments Excluding STRS JV's \| Systems Software
Investments, fair value	$ 26,398	$ 11,523
Percent of net assets	4.90%	2.00%
Investments Excluding STRS JV's \| Technology Hardware, Storage & Peripherals
Investments, fair value	$ 18,072	$ 16,745
Percent of net assets	3.40%	2.80%
Investments Excluding STRS JV's \| Transaction & Payment Processing Services
Investments, fair value	$ 8,066
Percent of net assets	1.50%
Investments Excluding STRS JV's \| Paper & Plastic Packaging Products & Materials
Investments, fair value		$ 179
Investments Excluding STRS JV's \| Wireless Telecommunication Services
Investments, fair value		$ 20,969
Percent of net assets		3.60%