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Note 6 - Derivative Instruments - Change in Fair Value of Derivatives (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Gain (losses) from derivative instruments | $ (16.4) | $ (17.9) | $ 56.2
Futures [Member] |  |  |
Gain (losses) from derivative instruments | (10.5) | (7.0) | 40.8
Credit Default Swaps [Member] |  |  |
Gain (losses) from derivative instruments | (3.0) | (6.5) | 3.7
Total Return Swaps [Member] |  |  |
Gain (losses) from derivative instruments | (9.3) | (12.8) | 21.3
Foreign Currency, Forward Contracts and Swaps [Member] |  |  |
Gain (losses) from derivative instruments | $ 6.4 | $ 8.4 | $ (9.6)

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- Definition Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-4A + Details
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