Note 4 - Derivative and Other Hedging Instruments (Details Textual) $ in Millions	Mar. 31, 2023 USD ($) $ / item	Dec. 31, 2022 USD ($) $ / item
Five Year Treasury Note Futures [Member] | Short [Member]
Derivative, Forward Price (in USD per Per Share) | $ / item	109.5	107.9
Derivative, Fair Value, Net	$ 1,014.6	$ 810.0
Derivative, Notional Amount	$ 926.5	$ 750.5
Ten Year Ultra Future [Member] | Short [Member]
Derivative, Forward Price (in USD per Per Share) | $ / item	121.1	118.3
Derivative, Fair Value, Net	$ 65.7	$ 206.4
Derivative, Notional Amount	54.2	$ 174.5
Interest Rate Swap [Member]
Derivative, Notional Amount	$ 274.0
Derivative, Fixed Interest Rate	3.43%