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CONSOLIDATED STATEMENTS OF CHANGES IN NET ASSETS (Parentheticals) - $ / shares | 12 Months Ended
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Mar. 31, 2024 | Mar. 31, 2023 | Mar. 31, 2022 | Mar. 31, 2021 | Mar. 31, 2020 | Mar. 31, 2019 | Mar. 31, 2018 | Mar. 31, 2017 | Mar. 31, 2016 | Mar. 31, 2015
Statement of Stockholders' Equity [Abstract] |  |  |  |  |  |  |  |  |  |
Net investment income (loss) (in USD per share) | $ 1.08 | $ 0.92 | $ 0.91 | $ 0.83 | $ 0.75 | $ 0.69 | $ 0.84 | $ 0.75 | $ 0.64 | $ 0.77
Gain (loss) on investment (in USD per share) | $ 1.12 | $ 0.49 | $ 0.26 | $ 0.10 | $ 0.28 | $ 0.24 | $ 0.05 | $ 0 | $ 0.11 | $ 0

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