Note 4 - Repurchase Agreements - Schedule of Repurchase Agreements (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Fair market value of securities pledged, including accrued interest receivable	$ 3,890,967	$ 3,900,476
Repurchase agreement liabilities associated with these securities	$ 3,711,498	$ 3,705,649
Net weighted average borrowing rate	5.46%	5.55%
Maturity Overnight [Member]
Fair market value of securities pledged, including accrued interest receivable	$ 94,362	$ 0
Repurchase agreement liabilities associated with these securities	$ 88,946	$ 0
Net weighted average borrowing rate	5.47%	0.00%
Maturity 2 to 30 Days [Member]
Fair market value of securities pledged, including accrued interest receivable	$ 3,406,836	$ 3,125,315
Repurchase agreement liabilities associated with these securities	$ 3,251,797	$ 2,966,650
Net weighted average borrowing rate	5.46%	5.55%
Maturity 30 to 90 Days [Member]
Fair market value of securities pledged, including accrued interest receivable	$ 361,390	$ 710,055
Repurchase agreement liabilities associated with these securities	$ 343,299	$ 674,696
Net weighted average borrowing rate	5.45%	5.54%
Maturity Greater than 90 Days [Member]
Fair market value of securities pledged, including accrued interest receivable	$ 28,379	$ 65,106
Repurchase agreement liabilities associated with these securities	$ 27,456	$ 64,303
Net weighted average borrowing rate	5.37%	5.46%