Note 5 - Derivative and Other Hedging Instruments (Details Textual) - Short [Member] $ in Millions	Sep. 30, 2025 USD ($) $ / item	Dec. 31, 2024 USD ($) $ / item
Five Year Treasury Note Futures [Member]
Derivative, Forward Price (in USD per Per Share) | $ / item	109.2	106.3
Derivative, Fair Value, Net | $	$ 614.2	$ 332.2
Ten Year T-Note Futures [Member]
Derivative, Forward Price (in USD per Per Share) | $ / item	112.5	108.75
Derivative, Fair Value, Net | $	$ 257.1	$ 101.7
Ten Year Ultra Futures [Member]
Derivative, Forward Price (in USD per Per Share) | $ / item	115.08	111.31
Derivative, Fair Value, Net | $	$ 227.3	$ 36.2