Note 2 - Mortgage-backed Securities and U.S. Treasury Securities, At Fair Value - Gain (Loss) on Investments (Details) - Collateralized Mortgage-Backed Securities [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Proceeds from sales of RMBS			$ 0	$ 2,731,497
Carrying value of RMBS sold			0	(2,864,169)
Realized losses on mortgage-backed securities	$ 0	$ (66,143)	0	(132,672)
Gross gain on sales of RMBS			0	2,705
Gross loss on sales of RMBS			$ 0	$ (135,377)