Note 2 - Mortgage-backed Securities, At Fair Value - Schedule of RMBS Portfolio (Details) - USD ($) $ in Thousands		Sep. 30, 2024	Dec. 31, 2023
Mortgage-backed securities, par value		$ 5,487,831	$ 4,051,145
Mortgage-backed securities, cost	[1]	5,632,872	4,220,088
Mortgage-backed securities, at fair value (includes pledged assets of $5,438,185 and $3,885,554, respectively)		5,442,804	3,894,012
Pass Through Certificate [Member]
Mortgage-backed securities, par value		5,487,831	4,051,145
Mortgage-backed securities, cost	[1]	5,613,352	4,198,424
Mortgage-backed securities, at fair value (includes pledged assets of $5,438,185 and $3,885,554, respectively)		5,427,069	3,877,082
Pass Through Certificate [Member] | Fixed Rate Mortgages [Member]
Mortgage-backed securities, par value		5,487,831	4,051,145
Mortgage-backed securities, cost	[1]	5,613,352	4,198,424
Mortgage-backed securities, at fair value (includes pledged assets of $5,438,185 and $3,885,554, respectively)		5,427,069	3,877,082
Structured Finance [Member]
Mortgage-backed securities, par value
Mortgage-backed securities, cost	[1]	19,520	21,664
Mortgage-backed securities, at fair value (includes pledged assets of $5,438,185 and $3,885,554, respectively)		15,735	16,930
Structured Finance [Member] | Interest Only Securities [Member]
Mortgage-backed securities, cost	[1],[2]	17,922	19,839
Mortgage-backed securities, at fair value (includes pledged assets of $5,438,185 and $3,885,554, respectively)	[2]	15,382	16,572
Structured Finance [Member] | Inverse Interest Only Securities [Member]
Mortgage-backed securities, cost	[1],[3]	1,598	1,825
Mortgage-backed securities, at fair value (includes pledged assets of $5,438,185 and $3,885,554, respectively)	[3]	$ 353	$ 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 $88.8 million and $98.6 million as of September 30, 2024 and December 31, 2023, respectively.

[3] The notional balance for the inverse interest-only securities portfolio was $23.4 million and $26.8 million as of September 30, 2024 and December 31, 2023, respectively.