Note 4 - Derivative and Other Hedging Instruments (Details Textual) - Short [Member] $ in Millions	Dec. 31, 2022 USD ($) $ / item	Dec. 31, 2021 USD ($) $ / item
Five Year Treasury Note Futures [Member]
Derivative, Forward Price (in USD per Per Share) | $ / item	107.93	120.98
Derivative, Fair Value, Net, Total | $	$ 810.0	$ 446.4
Ten Year Ultra Future [Member]
Derivative, Forward Price (in USD per Per Share) | $ / item	118.28	146.44
Derivative, Fair Value, Net, Total | $	$ 206.4	$ 322.2