Note 4 - Repurchase Agreements - Schedule of Repurchase Agreements (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair market value of securities pledged, including accrued interest receivable	$ 4,537,067	$ 3,524,059
Repurchase agreement liabilities associated with these securities	$ 4,426,947	$ 3,378,445
Net weighted average borrowing rate	5.49%	4.44%
Maturity Overnight [Member]
Fair market value of securities pledged, including accrued interest receivable	$ 0	$ 0
Repurchase agreement liabilities associated with these securities	$ 0	$ 0
Net weighted average borrowing rate	0.00%	0.00%
Maturity 2 to 30 Days [Member]
Fair market value of securities pledged, including accrued interest receivable	$ 2,346,245	$ 2,496,769
Repurchase agreement liabilities associated with these securities	$ 2,287,107	$ 2,404,329
Net weighted average borrowing rate	5.47%	4.43%
Maturity 30 to 90 Days [Member]
Fair market value of securities pledged, including accrued interest receivable	$ 2,190,822	$ 884,632
Repurchase agreement liabilities associated with these securities	$ 2,139,840	$ 837,299
Net weighted average borrowing rate	5.52%	4.51%
Maturity Greater than 90 Days [Member]
Fair market value of securities pledged, including accrued interest receivable	$ 0	$ 142,658
Repurchase agreement liabilities associated with these securities	$ 0	$ 136,817
Net weighted average borrowing rate	0.00%	4.15%