Note 6 - Pledged Assets - Schedule of Financial Instruments Owned and Pledged as Collateral (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Accrued interest receivable	$ 17,316	$ 11,519
Restricted cash	119,614	31,568
Asset Pledged as Collateral [Member]
Accrued interest receivable	17,299	11,435
Restricted cash	119,614	31,568
Total	4,747,116	3,592,025
Asset Pledged as Collateral [Member] | Residential Mortgage-Backed Securities [Member] | Pass Through Certificate [Member]
Investment at fair value	4,497,017	3,492,544
Asset Pledged as Collateral [Member] | Residential Mortgage-Backed Securities [Member] | Structured Finance [Member]
Investment at fair value	18,110	20,096
Asset Pledged as Collateral [Member] | US Treasury Securities [Member]
Investment at fair value	95,076	36,382
Asset Pledged as Collateral [Member] | Repurchase Agreements [Member]
Accrued interest receivable	17,299	11,419
Restricted cash	113,347	13,341
Total	4,650,414	3,537,400
Asset Pledged as Collateral [Member] | Repurchase Agreements [Member] | Residential Mortgage-Backed Securities [Member] | Pass Through Certificate [Member]
Investment at fair value	4,497,017	3,492,544
Asset Pledged as Collateral [Member] | Repurchase Agreements [Member] | Residential Mortgage-Backed Securities [Member] | Structured Finance [Member]
Investment at fair value	18,110	20,096
Asset Pledged as Collateral [Member] | Repurchase Agreements [Member] | US Treasury Securities [Member]
Investment at fair value	4,641	0
Asset Pledged as Collateral [Member] | Derivative [Member]
Accrued interest receivable	0	16
Restricted cash	6,267	18,227
Total	96,702	54,625
Asset Pledged as Collateral [Member] | Derivative [Member] | Residential Mortgage-Backed Securities [Member] | Pass Through Certificate [Member]
Investment at fair value	0	0
Asset Pledged as Collateral [Member] | Derivative [Member] | Residential Mortgage-Backed Securities [Member] | Structured Finance [Member]
Investment at fair value	0	0
Asset Pledged as Collateral [Member] | Derivative [Member] | US Treasury Securities [Member]
Investment at fair value	$ 90,435	$ 36,382