Note 4 - Repurchase Agreements and Reverse Purchase Agreements - Schedule of Repurchase Agreements (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Fair value of securities pledged, including accrued interest receivable	$ 11,310,983	$ 10,551,280
Repurchase agreement liabilities associated with these securities	$ 10,864,723	$ 10,115,466
Net weighted average borrowing rate	3.79%	3.98%
Maturity Overnight [Member]
Fair 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 value of securities pledged, including accrued interest receivable	$ 6,444,148	$ 6,821,306
Repurchase agreement liabilities associated with these securities	$ 6,180,946	$ 6,544,072
Net weighted average borrowing rate	3.79%	4.00%
Maturity 30 to 90 Days [Member]
Fair value of securities pledged, including accrued interest receivable	$ 3,662,811	$ 3,445,678
Repurchase agreement liabilities associated with these securities	$ 3,529,429	$ 3,297,567
Net weighted average borrowing rate	3.78%	3.96%
Maturity Greater than 90 Days [Member]
Fair value of securities pledged, including accrued interest receivable	$ 1,204,024	$ 284,296
Repurchase agreement liabilities associated with these securities	$ 1,154,348	$ 273,827
Net weighted average borrowing rate	3.82%	3.92%