Note 5 - Derivative and Other Hedging Instruments (Details Textual) - Short [Member] $ in Millions	Mar. 31, 2025 USD ($) $ / item	Dec. 31, 2024 USD ($) $ / item
Five Year Treasury Note Futures [Member]
Derivative, Forward Price (in USD per Per Share) | $ / item	108.16	106.3
Derivative, Fair Value, Net | $	$ 408.3	$ 332.2
Ten Year T-Note Futures [Member]
Derivative, Forward Price (in USD per Per Share) | $ / item	111.22	108.75
Derivative, Fair Value, Net | $	$ 215.2	$ 101.6
Ten Year Ultra Futures [Member]
Derivative, Forward Price (in USD per Per Share) | $ / item	114.13	111.31
Derivative, Fair Value, Net | $	$ 156.9	$ 36.2