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Note 9 - Concentrations of Credit Risk (Details Textual) - Debt Investments [Member] | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023 | Dec. 31, 2023
Investment Concentration Risk [Member] | Reported Value Measurement [Member] |  |  |  |  |
Concentration Risk, Percentage |  |  | 22.00% |  | 23.00%
Investment Concentration Risk [Member] | Estimate of Fair Value Measurement [Member] |  |  |  |  |
Concentration Risk, Percentage |  |  | 23.00% |  | 22.00%
Interest Income [Member] | Reported Value Measurement [Member] |  |  |  |  |
Concentration Risk, Percentage | 21.00% | 24.00% | 21.00% | 23.00% |
Interest Income [Member] | Estimate of Fair Value Measurement [Member] |  |  |  |  |
Concentration Risk, Percentage | 25.00% | 22.00% | 23.00% | 21.00% |

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