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DISTRIBUTIONS TO COMMON STOCKHOLDERS - Narrative (Details) | 12 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2025 USD ($) distribution | Sep. 30, 2024 USD ($) | Sep. 30, 2023 USD ($) | Dec. 31, 2024 | Dec. 31, 2023
Equity [Abstract] |  |  |  |  |
Number of monthly distributions | distribution | 3 |  |  |  |
Investment company, cash distributions paid to common stockholders from ordinary income |  |  |  | 83.10% | 100.00%
Investment company, cash distributions paid to common stockholders from capital gains |  |  |  | 16.90% |
Cash distributions to common stockholders | $ 55,500,000 | $ 43,100,000 |  |  |
Undistributed ordinary income | 5,481,000 | 6,590,000 | $ 5,000,000.0 |  |
Tax return of capital distribution | $ 700,000 | $ 0 | $ 0 |  |

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