Note 2 - Mortgage-backed Securities, At Fair Value - Schedule of RMBS Portfolio (Details) - USD ($) $ in Thousands		Mar. 31, 2024	Dec. 31, 2023
Mortgage-backed securities, par value		$ 4,351,259	$ 4,051,145
Mortgage-backed securities, cost	[1]	4,487,493	4,220,088
Mortgage-backed securities		3,881,078	3,894,012
Pass Through Certificate [Member]
Mortgage-backed securities, par value		4,351,259	4,051,145
Mortgage-backed securities, cost	[1]	4,466,595	4,198,424
Mortgage-backed securities		3,864,505	3,877,082
Pass Through Certificate [Member] | Fixed Rate Mortgages [Member]
Mortgage-backed securities, par value		4,351,259	4,051,145
Mortgage-backed securities, cost	[1]	4,466,595	4,198,424
Mortgage-backed securities		3,864,505	3,877,082
Structured Finance [Member]
Mortgage-backed securities, par value
Mortgage-backed securities, cost	[1]	20,898	21,664
Mortgage-backed securities		16,573	16,930
Structured Finance [Member] | Interest Only Securities [Member]
Mortgage-backed securities, cost	[1],[2]	19,142	19,839
Mortgage-backed securities	[2]	16,326	16,572
Structured Finance [Member] | Inverse Interest Only Securities [Member]
Mortgage-backed securities, cost	[1],[3]	1,756	1,825
Mortgage-backed securities	[3]	$ 247	$ 358

[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.

[2] The notional balance for the interest-only securities portfolio was $94.9 million and $98.6 million as of March 31, 2024 and December 31, 2023, respectively.

[3] The notional balance for the inverse interest-only securities portfolio was $25.8 million and $26.8 million as of March 31, 2024 and December 31, 2023, respectively.