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INVESTMENTS - Narrative (Details) $ in Thousands | 1 Months Ended | 3 Months Ended | 6 Months Ended |  |  |
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Sep. 30, 2025 USD ($) industry portfolioCompany state | Jul. 31, 2025 USD ($) | May 31, 2025 USD ($) | Sep. 30, 2025 USD ($) industry portfolioCompany state | Sep. 30, 2024 USD ($) | Sep. 30, 2025 USD ($) industry portfolioCompany state | Sep. 30, 2024 USD ($) | Aug. 31, 2025 USD ($) | Jun. 30, 2025 USD ($) | Mar. 31, 2025 USD ($)
Summary of Investment Holdings [Line Items] |  |  |  |  |  |  |  |  |  |  |
Purchase of investments |  |  |  |  |  | $ 133,878 | $ 20,098 |  |  |  |
Investments, cost | $ 1,037,200 |  |  | $ 1,037,200 |  | 1,037,200 |  |  |  | $ 939,066 | [1]
Net realized gain (loss) |  |  |  | $ (29,938) | $ 42,303 | $ (29,938) | $ 42,305 |  |  |  |
Number of investment portfolio company | portfolioCompany | 28 |  |  | 28 |  | 28 |  |  |  |  |
Number of states or countries which have invested in the company location | state | 20 |  |  | 20 |  | 20 |  |  |  |  |
Number of industries that have made investments | industry | 16 |  |  | 16 |  | 16 |  |  |  |  |
Investments owned, fair value | $ 1,130,859 |  |  | $ 1,130,859 |  | $ 1,130,859 |  |  |  | 979,320 | [1]
Uncollectible receivables allowance, minimum required day for uncollectible adjustment |  |  |  |  |  | 90 days |  |  |  |  |
Gross receivables from portfolio companies | 2,400 |  |  | 2,400 |  | $ 2,400 |  |  |  | 2,300 |
Allowance for uncollectible receivables | 1,400 |  |  | 1,400 |  | 1,400 |  |  |  | 1,700 |
Five Largest Portfolio Investments | Investment Portfolio Benchmark | Customer Concentration Risk |  |  |  |  |  |  |  |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |  |  |  |  |  |  |  |
Investments owned, fair value | 437,400 |  |  | 437,400 |  | $ 437,400 |  |  |  |  |
Percentage of total investments |  |  |  |  |  | 38.70% |  |  |  |  |
Secured First Lien Debt |  |  |  |  |  |  |  |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |  |  |  |  |  |  |  |
Investments, cost | 644,158 |  |  | 644,158 |  | $ 644,158 |  |  |  | 584,026 |
Investments owned, fair value | 593,979 |  |  | 593,979 |  | 593,979 |  |  |  | 514,334 |
Preferred Equity |  |  |  |  |  |  |  |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |  |  |  |  |  |  |  |
Investments, cost | 250,105 |  |  | 250,105 |  | 250,105 |  |  |  | 201,487 |
Investments owned, fair value | 365,278 |  |  | $ 365,278 |  | $ 365,278 |  |  |  | $ 302,163 |
Smart Chemical |  |  |  |  |  |  |  |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |  |  |  |  |  |  |  |
Purchase of investments |  |  | $ 49,500 |  |  |  |  |  |  |  |
Smart Chemical | Secured First Lien Debt |  |  |  |  |  |  |  |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |  |  |  |  |  |  |  |
Purchase of investments |  |  | 35,700 |  |  |  |  |  |  |  |
Smart Chemical | Preferred Equity |  |  |  |  |  |  |  |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |  |  |  |  |  |  |  |
Purchase of investments |  |  | 13,800 |  |  |  |  |  |  |  |
Sun State |  |  |  |  |  |  |  |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |  |  |  |  |  |  |  |
Purchase of investments |  |  | 12,800 |  |  |  |  |  |  |  |
Sun State | Secured First Lien Debt |  |  |  |  |  |  |  |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |  |  |  |  |  |  |  |
Purchase of investments |  |  | 9,800 |  |  |  |  |  |  |  |
Sun State | Preferred Equity |  |  |  |  |  |  |  |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |  |  |  |  |  |  |  |
Purchase of investments |  |  | $ 3,100 |  |  |  |  |  |  |  |
PSI Molded |  |  |  |  |  |  |  |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |  |  |  |  |  |  |  |
Investments, cost |  |  |  |  |  |  |  |  | $ 10,600 |  |
Global GRAB Technologies, Inc., ("Global GRAB") |  |  |  |  |  |  |  |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |  |  |  |  |  |  |  |
Purchase of investments |  | $ 67,600 |  |  |  |  |  |  |  |  |
Global GRAB Technologies, Inc., ("Global GRAB") | Secured First Lien Debt |  |  |  |  |  |  |  |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |  |  |  |  |  |  |  |
Purchase of investments |  | 46,500 |  |  |  |  |  |  |  |  |
Global GRAB Technologies, Inc., ("Global GRAB") | Preferred Equity |  |  |  |  |  |  |  |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |  |  |  |  |  |  |  |
Purchase of investments |  | $ 21,100 |  |  |  |  |  |  |  |  |
J.R. Hobbs |  |  |  |  |  |  |  |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |  |  |  |  |  |  |  |
Purchase of investments | 20,000 |  |  |  |  |  |  |  |  |  |
Investments, cost |  |  |  |  |  |  |  | $ 49,900 |  |  |
Net realized gain (loss) | $ (29,900) |  |  |  |  |  |  |  |  |  |
[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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