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Note 3 - Investments - Schedule of Debt Securities, Held-to-Maturity Credit Quality Indicators (Details) - USD ($) $ in Millions | Mar. 31, 2024 | Dec. 31, 2023
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Debt Securities, Held-to-Maturity, Amortized Cost | $ 8.5 | $ 8.5
Standard & Poor's, BBB/BBB Minus Rating [Member] |  |
Debt Securities, Held-to-Maturity, Amortized Cost | 7.0 | 7.0
Standard & Poor's, BB+ Rating [Member] |  |
Debt Securities, Held-to-Maturity, Amortized Cost | $ 1.5 | $ 1.5

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