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Note 6 - Derivative Instruments - Derivative Instruments (Details) - USD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023
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Futures [Member] |  |
Notional value of derivative | $ 789.0 | $ 1,018.0
Futures [Member] | Seeded Investment Products [Member] |  |
Notional value of derivative | 160.5 | 1,555.1
Foreign Currency, Forward Contracts and Swaps [Member] |  |
Notional value of derivative | 328.2 | 176.2
Foreign Currency, Forward Contracts and Swaps [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member] |  |
Notional value of derivative | 38.4 | 65.3
Foreign Currency, Forward Contracts and Swaps [Member] | Seeded Investment Products [Member] |  |
Notional value of derivative | 196.6 | 135.3
Credit Default Swaps [Member] |  |
Notional value of derivative | 148.5 | 199.7
Credit Default Swaps [Member] | Seeded Investment Products [Member] |  |
Notional value of derivative | 4.3 | 13.2
Total Return Swaps [Member] |  |
Notional value of derivative | 69.7 | 51.8
Total Return Swaps [Member] | Seeded Investment Products [Member] |  |
Notional value of derivative | 10.3 | 0.3
Interest Rate Swap [Member] | Seeded Investment Products [Member] |  |
Notional value of derivative | 13.9 | 2.2
Other [Member] | Seeded Investment Products [Member] |  |
Notional value of derivative | $ 0.0 | $ 0.3

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- Definition Nominal or face amount used to calculate payment on derivative. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-1B Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1A -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A + Details
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