| CONSOLIDATED STATEMENTS OF CHANGES IN NET ASSETS (Parentheticals) - $ / shares | 12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2015 | |
| Statement of Stockholders' Equity [Abstract] | ||||||||||
| Net investment income (in USD per share) | $ 1.98 | $ 1.89 | $ 1.52 | $ 1.50 | $ 1.60 | $ 1.64 | $ 1.68 | $ 1.68 | $ 1.40 | $ 1.68 | 
| Return of capital (in USD per share) | $ 0.00 | $ 0.00 | $ 0.08 | $ 0.06 | $ 0.02 | $ 0.04 | $ 0 | $ 0 | $ 0 | $ 0 | 
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- Definition Investment Company, Distribution to Shareholders from Net Investment Income, Per Share No definition available. 
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- Definition Investment Company, Distribution To Shareholders From Return Of Capital, Per Share No definition available. 
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- References No definition available. 
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