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Note 5 - Derivative Instruments - Change in Fair Value of Derivatives (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
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Jun. 30, 2025 | Jun. 30, 2024 | Jun. 30, 2025 | Jun. 30, 2024
Gain (losses) from derivative instruments | $ (26.3) | $ (0.2) | $ (24.2) | $ (11.9)
Futures [Member] |  |  |  |
Gain (losses) from derivative instruments | (20.8) | 2.9 | (23.1) | (5.8)
Credit Default Swaps [Member] |  |  |  |
Gain (losses) from derivative instruments | (1.2) | (0.1) | (0.6) | (1.5)
Total Return Swaps [Member] |  |  |  |
Gain (losses) from derivative instruments | (7.1) | (1.3) | (5.5) | (5.9)
Foreign Currency, Forward Contracts and Swaps [Member] |  |  |  |
Gain (losses) from derivative instruments | 3.2 | (1.8) | 5.4 | 0.9
TBAs [Member] |  |  |  |
Gain (losses) from derivative instruments | $ (0.4) | $ 0.1 | $ (0.4) | $ 0.4

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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://www.xbrl.org/2009/role/commonPracticeRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4A -Subparagraph (b)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-4A + Details
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