Note 2 - Mortgage-backed Securities and U.S. Treasury Notes - Gain (Loss) on Investments (Details) - Collateralized Mortgage-Backed Securities [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Proceeds from sales of RMBS	$ 0	$ 1,413,039
Carrying value of RMBS sold	0	(1,464,125)
Realized losses on mortgage-backed securities	0	(51,086)
Gross gain on sales of RMBS	0	709
Gross loss on sales of RMBS	$ 0	$ (51,795)