Note 5 - Pledged Assets - Schedule of Financial Instruments Owned and Pledged as Collateral (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Accrued interest receivable	$ 11,519	$ 18,859
Restricted cash	31,568	65,299
Asset Pledged as Collateral [Member]
Accrued interest receivable	11,435	18,817
Restricted cash	31,568	65,299
Total	3,592,025	6,620,228
Asset Pledged as Collateral [Member] | Residential Mortgage-Backed Securities [Member] | Pass Through Certificate [Member]
Investment at fair value	3,492,544	6,294,102
Asset Pledged as Collateral [Member] | Residential Mortgage-Backed Securities [Member] | Structured Finance [Member]
Investment at fair value	20,096	212,270
Asset Pledged as Collateral [Member] | US Treasury Securities [Member]
Investment at fair value	36,382	29,740
Asset Pledged as Collateral [Member] | Repurchase Agreements [Member]
Accrued interest receivable	11,419	18,804
Restricted cash	13,341	57,264
Total	3,537,400	6,582,440
Asset Pledged as Collateral [Member] | Repurchase Agreements [Member] | Residential Mortgage-Backed Securities [Member] | Pass Through Certificate [Member]
Investment at fair value	3,492,544	6,294,102
Asset Pledged as Collateral [Member] | Repurchase Agreements [Member] | Residential Mortgage-Backed Securities [Member] | Structured Finance [Member]
Investment at fair value	20,096	212,270
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	16	13
Restricted cash	18,227	8,035
Total	54,625	37,788
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	$ 36,382	$ 29,740