Note 6 - Offsetting Assets and Liabilities - Offsetting Liabilities (Details) - Liability [Member] - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Gross amount recognized	$ 3,385,606	$ 6,251,695
Gross amount offset in the balance sheet	0	0
Net amount presented in the balance sheet	3,385,606	6,251,695
Gross amount not offset in the balance sheet, financial instruments posted as collateral	(3,365,104)	(6,189,704)
Gross amount not offset in the balance sheet, cash posted as collateral	(14,520)	(57,264)
Net amount	5,982	4,727
Repurchase Agreements [Member]
Gross amount recognized	3,378,445	6,244,106
Gross amount offset in the balance sheet	0	0
Net amount presented in the balance sheet	3,378,445	6,244,106
Gross amount not offset in the balance sheet, financial instruments posted as collateral	(3,365,104)	(6,186,842)
Gross amount not offset in the balance sheet, cash posted as collateral	(13,341)	(57,264)
Net amount	0	0
Interest Rate Swap [Member]
Gross amount recognized	0	2,862
Gross amount offset in the balance sheet	0	0
Net amount presented in the balance sheet	0	2,862
Gross amount not offset in the balance sheet, financial instruments posted as collateral	0	(2,862)
Gross amount not offset in the balance sheet, cash posted as collateral	0	0
Net amount	0	0
Payer Swaptions [Member]
Gross amount recognized	5,982	4,423
Gross amount offset in the balance sheet	0	0
Net amount presented in the balance sheet	5,982	4,423
Gross amount not offset in the balance sheet, financial instruments posted as collateral	0	0
Gross amount not offset in the balance sheet, cash posted as collateral	0	0
Net amount	5,982	4,423
TBA Contracts [Member]
Gross amount recognized	1,179	304
Gross amount offset in the balance sheet	0	0
Net amount presented in the balance sheet	1,179	304
Gross amount not offset in the balance sheet, financial instruments posted as collateral	0	0
Gross amount not offset in the balance sheet, cash posted as collateral	(1,179)	0
Net amount	$ 0	$ 304