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Note 4 - Investments (Details Textual) - USD ($) $ in Millions | 6 Months Ended
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Jun. 30, 2025 | Jun. 30, 2024
Debt Securities, Trading, Unrealized Gain (Loss) | $ 61.5 | $ 35.6
European Smaller Companies Trust PLC [Member] |  |
Other Investments | $ 53.7 |
Privacore [Member] |  |
Equity Method Investment, Ownership Percentage | 49.00% |
Long Tail Alpha Investment [Member] |  |
Equity Method Investment, Ownership Percentage | 20.00% |

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- Definition Amount of unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in net income (trading). + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Name Accounting Standards Codification -Section 55 -Paragraph 10 -SubTopic 10 -Topic 825 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482881/825-10-55-10 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 14 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-14 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 9 -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-9 + Details
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- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 825 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 28 -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482907/825-10-50-28 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 323 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481687/323-10-50-3 + Details
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