Note 6 - Pledged Assets - Schedule of Financial Instruments Owned and Pledged as Collateral (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Accrued interest receivable	$ 14,951	$ 11,519
Restricted cash	28,396	31,568
Asset Pledged as Collateral [Member]
Accrued interest receivable	14,922	11,435
Restricted cash	28,396	31,568
Total	4,008,552	3,592,025
Asset Pledged as Collateral [Member] | Residential Mortgage-Backed Securities [Member] | Pass Through Certificate [Member]
Investment at fair value	3,868,624	3,492,544
Asset Pledged as Collateral [Member] | Residential Mortgage-Backed Securities [Member] | Structured Finance [Member]
Investment at fair value	16,930	20,096
Asset Pledged as Collateral [Member] | US Treasury Securities [Member]
Investment at fair value	79,680	36,382
Asset Pledged as Collateral [Member] | Repurchase Agreements [Member]
Accrued interest receivable	14,922	11,419
Restricted cash		13,341
Total	3,900,476	3,537,400
Asset Pledged as Collateral [Member] | Repurchase Agreements [Member] | Residential Mortgage-Backed Securities [Member] | Pass Through Certificate [Member]
Investment at fair value	3,868,624	3,492,544
Asset Pledged as Collateral [Member] | Repurchase Agreements [Member] | Residential Mortgage-Backed Securities [Member] | Structured Finance [Member]
Investment at fair value	16,930	20,096
Asset Pledged as Collateral [Member] | Derivative [Member]
Accrued interest receivable		16
Restricted cash	28,396	18,227
Total	$ 108,076	$ 54,625