Note 9 - Federal Income Taxes - Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Tax at U.S. statutory rate	$ 21,734	$ 20,640	$ 21,567
Tax at U.S. statutory rate, percent	21.00%	21.00%	21.00%
Tax credits net of proportional amortization and tax losses	$ (1,929)	$ (266)	$ 24
Tax credits net of proportional amortization and tax losses, percent	(1.90%)	(0.30%)	0.00%
Discount of purchased tax credits	$ (3,525)
Discount of purchased tax credits, percent	(3.40%)
Tax-exempt interest, net of interest expense disallowance	$ (1,265)	$ (1,027)	$ (862)
Tax-exempt interest, net of interest expense disallowance, percent	(1.20%)	(1.00%)	(0.80%)
Bank owned life insurance, amount	$ (683)	$ (529)	$ (303)
Bank owned life insurance, percent	(0.70%)	(0.50%)	(0.30%)
Non-deductible expenses, amount	$ 538	$ 241	$ 213
Non-deductible expenses, percent	0.50%	0.20%	0.20%
Other, amount	$ (130)	$ (366)	$ (157)
Other, percent	(0.10%)	(0.40%)	(0.20%)
Tax expense	$ 14,740	$ 18,693	$ 20,482
Tax expense, percent	14.20%	19.00%	19.90%