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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 | 9 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Gain (losses) from derivative instruments | $ (27.1) | $ (11.3) | $ (51.3) | $ (23.6)
Futures [Member] |  |  |  |
Gain (losses) from derivative instruments | (19.0) | (16.6) | (42.1) | (22.4)
Credit Default Swaps [Member] |  |  |  |
Gain (losses) from derivative instruments | (0.8) | (1.0) | (1.4) | (2.5)
Total Return Swaps [Member] |  |  |  |
Gain (losses) from derivative instruments | (1.8) | (3.4) | (7.3) | (9.3)
Foreign Currency, Forward Contracts and Swaps [Member] |  |  |  |
Gain (losses) from derivative instruments | (5.2) | 9.7 | 0.2 | 10.6
TBAs [Member] |  |  |  |
Gain (losses) from derivative instruments | $ (0.3) | $ 0.0 | $ (0.7) | $ 0.0

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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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