Note 2 - Mortgage-backed Securities and U.S. Treasury Securities, at Fair Value - Schedule of RMBS Portfolio (Details) - USD ($) $ in Thousands		Dec. 31, 2025	Dec. 31, 2024
Mortgage-backed securities, par value		$ 10,345,029	$ 5,431,274
Mortgage-backed securities, cost	[1]	10,574,339	5,559,428
Pledged assets, Mortgage-backed securities		10,628,658	5,253,310
Fixed Rate Mortgages [Member]
Mortgage-backed securities, par value		10,345,029	5,431,274
Mortgage-backed securities, cost	[1]	10,558,236	5,540,596
Pledged assets, Mortgage-backed securities		10,615,570	5,237,812
Financial Instrument, Other [Member]
Mortgage-backed securities, par value		0	0
Mortgage-backed securities, cost	[1]	16,103	18,832
Pledged assets, Mortgage-backed securities		$ 13,088	$ 15,498

[1] The cost information in the table above represents the aggregate current par value, multiplied by the purchase price of each security in the portfolio.