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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
	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

X

- 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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Details

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Namespace Prefix:
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X

- Details

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X

- Details

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X

- Details

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X

- Details

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X

- Details

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