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Note 10 - Concentrations of Credit Risk (Details Textual) - Debt Investments [Member] | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Investment Concentration Risk [Member] | Reported Value Measurement [Member] |  |  |
Concentration Risk, Percentage | 23.00% | 23.00% |
Investment Concentration Risk [Member] | Estimate of Fair Value Measurement [Member] |  |  |
Concentration Risk, Percentage | 22.00% | 23.00% |
Interest Income [Member] | Reported Value Measurement [Member] |  |  |
Concentration Risk, Percentage | 17.00% | 15.00% | 17.00%
Interest Income [Member] | Estimate of Fair Value Measurement [Member] |  |  |
Concentration Risk, Percentage | 15.00% | 15.00% | 17.00%

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- Definition For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 42 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482810/280-10-50-42 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 21 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482907/825-10-50-21 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 20 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482907/825-10-50-20 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482861/275-10-50-18 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 20 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482861/275-10-50-20 + Details
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