Note 6 - Pledged Assets - Schedule of Financial Instruments Owned and Pledged as Collateral (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Accrued interest receivable	$ 15,614	$ 14,951
Restricted cash	13,247	28,396
Asset Pledged as Collateral [Member]
Accrued interest receivable	15,598	14,922
Restricted cash	13,247	28,396
Total	3,984,140	4,008,552
Asset Pledged as Collateral [Member] | Residential Mortgage-Backed Securities [Member] | Pass Through Certificate [Member]
Investment at fair value	3,859,132	3,868,624
Asset Pledged as Collateral [Member] | Residential Mortgage-Backed Securities [Member] | Structured Finance [Member]
Investment at fair value	16,573	16,930
Asset Pledged as Collateral [Member] | US Treasury Securities [Member]
Investment at fair value	79,590	79,680
Asset Pledged as Collateral [Member] | Repurchase Agreements [Member]
Accrued interest receivable	15,262	14,922
Restricted cash	7,418
Total	3,898,385	3,900,476
Asset Pledged as Collateral [Member] | Repurchase Agreements [Member] | Residential Mortgage-Backed Securities [Member] | Pass Through Certificate [Member]
Investment at fair value	3,859,132	3,868,624
Asset Pledged as Collateral [Member] | Repurchase Agreements [Member] | Residential Mortgage-Backed Securities [Member] | Structured Finance [Member]
Investment at fair value	16,573	16,930
Asset Pledged as Collateral [Member] | Derivative [Member]
Accrued interest receivable	336	0
Restricted cash	5,829	28,396
Total	85,755	108,076
Asset Pledged as Collateral [Member] | Derivative [Member] | US Treasury Securities [Member]
Investment at fair value	$ 79,590	$ 79,680