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INVESTMENTS - Schedule of Investment Concentrations (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2025 | Mar. 31, 2025
Summary of Investment Holdings [Line Items] |  |  |
Cost | $ 997,538 | $ 939,066 | [1]
Fair Value | 1,036,745 | 979,320 | [1]
PSI Molded |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Cost | 10,600 |  |
South |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 389,680 | 317,294 |
West |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 229,132 | 222,062 |
Midwest |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 212,997 | 227,415 |
Northeast |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 176,909 | 182,669 |
Canada |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 28,027 | 29,880 |
Diversified/Conglomerate Services |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 188,845 | 170,360 |
Home and Office Furnishings, Housewares, and Durable Consumer Products |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 150,749 | 159,236 |
Machinery (Non-Agriculture, Non-Construction, and Non-Electronic) |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 109,985 | 105,432 |
Aerospace and Defense |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 105,170 | 107,869 |
Leisure, Amusement, Motion Pictures, and Entertainment |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 79,588 | 78,460 |
Oil and Gas |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 72,286 | 69,589 |
Electronics |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 71,334 | 71,573 |
Buildings and Real Estate |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 69,075 | 69,320 |
Chemicals, Plastics, and Rubber |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 54,980 | 11,612 |
Healthcare, Education, and Childcare |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 48,197 | 51,501 |
Mining, Steel, Iron and Non-Precious Metals |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 43,505 | 41,010 |
Cargo Transport |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 13,000 | 12,624 |
Printing and Publishing |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | 12,611 | 11,681 |
Other less than 2.0% |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Fair Value | $ 17,420 | $ 19,053 |
Investment Owned, at Cost | Investment Type Concentration Risk |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 100.00% | 100.00% |
Investment Owned, at Fair Value | Investment Type Concentration Risk |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 100.00% | 100.00% |
Investment Owned, at Fair Value | Industry Concentration Risk |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 100.00% | 100.00% |
Investment Owned, at Fair Value | Industry Concentration Risk | Diversified/Conglomerate Services |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 18.20% | 17.40% |
Investment Owned, at Fair Value | Industry Concentration Risk | Home and Office Furnishings, Housewares, and Durable Consumer Products |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 14.50% | 16.30% |
Investment Owned, at Fair Value | Industry Concentration Risk | Machinery (Non-Agriculture, Non-Construction, and Non-Electronic) |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 10.60% | 10.80% |
Investment Owned, at Fair Value | Industry Concentration Risk | Aerospace and Defense |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 10.10% | 10.90% |
Investment Owned, at Fair Value | Industry Concentration Risk | Leisure, Amusement, Motion Pictures, and Entertainment |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 7.70% | 8.00% |
Investment Owned, at Fair Value | Industry Concentration Risk | Oil and Gas |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 7.00% | 7.10% |
Investment Owned, at Fair Value | Industry Concentration Risk | Electronics |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 6.90% | 7.20% |
Investment Owned, at Fair Value | Industry Concentration Risk | Buildings and Real Estate |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 6.70% | 7.10% |
Investment Owned, at Fair Value | Industry Concentration Risk | Chemicals, Plastics, and Rubber |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 5.30% | 1.20% |
Investment Owned, at Fair Value | Industry Concentration Risk | Healthcare, Education, and Childcare |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 4.60% | 5.30% |
Investment Owned, at Fair Value | Industry Concentration Risk | Mining, Steel, Iron and Non-Precious Metals |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 4.20% | 4.20% |
Investment Owned, at Fair Value | Industry Concentration Risk | Cargo Transport |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 1.30% | 1.30% |
Investment Owned, at Fair Value | Industry Concentration Risk | Printing and Publishing |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 1.20% | 1.20% |
Investment Owned, at Fair Value | Industry Concentration Risk | Other less than 2.0% |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 1.70% | 2.00% |
Investment Owned, at Fair Value | Geographic Regions Risk |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 100.00% | 100.00% |
Investment Owned, at Fair Value | Geographic Regions Risk | South |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 37.60% | 32.40% |
Investment Owned, at Fair Value | Geographic Regions Risk | West |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 22.10% | 22.70% |
Investment Owned, at Fair Value | Geographic Regions Risk | Midwest |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 20.50% | 23.20% |
Investment Owned, at Fair Value | Geographic Regions Risk | Northeast |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 17.10% | 18.70% |
Investment Owned, at Fair Value | Geographic Regions Risk | Canada |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 2.70% | 3.00% |
Total debt |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Cost | $ 718,936 | $ 687,982 |
Fair Value | $ 650,397 | $ 617,914 |
Total debt | Investment Owned, at Cost | Investment Type Concentration Risk |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 72.10% | 73.30% |
Total debt | Investment Owned, at Fair Value | Investment Type Concentration Risk |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 62.70% | 63.10% |
Secured First Lien Debt |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Cost | $ 625,596 | $ 584,026 |
Fair Value | $ 557,057 | $ 514,334 |
Secured First Lien Debt | Investment Owned, at Cost | Investment Type Concentration Risk |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 62.70% | 62.20% |
Secured First Lien Debt | Investment Owned, at Fair Value | Investment Type Concentration Risk |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 53.70% | 52.50% |
Secured Second Lien Debt |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Cost | $ 93,340 | $ 103,956 |
Fair Value | $ 93,340 | $ 103,580 |
Secured Second Lien Debt | Investment Owned, at Cost | Investment Type Concentration Risk |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 9.40% | 11.10% |
Secured Second Lien Debt | Investment Owned, at Fair Value | Investment Type Concentration Risk |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 9.00% | 10.60% |
Total equity/equivalents |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Cost | $ 278,602 | $ 251,084 |
Fair Value | $ 386,348 | $ 361,406 |
Total equity/equivalents | Investment Owned, at Cost | Investment Type Concentration Risk |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 27.90% | 26.70% |
Total equity/equivalents | Investment Owned, at Fair Value | Investment Type Concentration Risk |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 37.30% | 36.90% |
Preferred Equity |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Cost | $ 229,005 | $ 201,487 |
Fair Value | $ 325,997 | $ 302,163 |
Preferred Equity | Investment Owned, at Cost | Investment Type Concentration Risk |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 23.00% | 21.50% |
Preferred Equity | Investment Owned, at Fair Value | Investment Type Concentration Risk |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 31.50% | 30.90% |
Common Equity/ Equivalents |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Cost | $ 49,597 | $ 49,597 |
Fair Value | $ 60,351 | $ 59,243 |
Common Equity/ Equivalents | Investment Owned, at Cost | Investment Type Concentration Risk |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 4.90% | 5.20% |
Common Equity/ Equivalents | Investment Owned, at Fair Value | Investment Type Concentration Risk |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Percentage of Total Investments | 5.80% | 6.00% |
[1] | Cumulative gross unrealized appreciation for federal income tax purposes is $183.3 million; cumulative gross unrealized depreciation for federal income tax purposes is $144.9 million. Cumulative net unrealized appreciation is $38.5 million, based on a tax cost of $940.9 million.

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