Note 5 - Pledged Assets - Schedule of Financial Instruments Owned and Pledged as Collateral (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Accrued interest receivable	$ 13,120	$ 11,519
Restricted cash	42,738	31,568
Asset Pledged as Collateral [Member]
Accrued interest receivable	12,871	11,435
Restricted cash	42,738	31,568
Total	4,038,571	3,592,025
Asset Pledged as Collateral [Member] | Residential Mortgage-Backed Securities [Member] | Pass Through Certificate [Member]
Investment at fair value	3,926,711	3,492,544
Asset Pledged as Collateral [Member] | Residential Mortgage-Backed Securities [Member] | Structured Finance [Member]
Investment at fair value	19,445	20,096
Asset Pledged as Collateral [Member] | US Treasury Securities [Member]
Investment at fair value	36,806	36,382
Asset Pledged as Collateral [Member] | Repurchase Agreements [Member]
Accrued interest receivable	12,867	11,419
Restricted cash	18,072	13,341
Total	3,977,095	3,537,400
Asset Pledged as Collateral [Member] | Repurchase Agreements [Member] | Residential Mortgage-Backed Securities [Member] | Pass Through Certificate [Member]
Investment at fair value	3,926,711	3,492,544
Asset Pledged as Collateral [Member] | Repurchase Agreements [Member] | Residential Mortgage-Backed Securities [Member] | Structured Finance [Member]
Investment at fair value	19,445	20,096
Asset Pledged as Collateral [Member] | Repurchase Agreements [Member] | US Treasury Securities [Member]
Investment at fair value	0	0
Asset Pledged as Collateral [Member] | Derivative [Member]
Accrued interest receivable	4	16
Restricted cash	24,666	18,227
Total	61,476	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	$ 36,806	$ 36,382