Note 7 - Income Taxes - Difference Between Statutory and Effective Tax Rates (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
U.S. federal statutory income tax rate	21.00%	21.00%	21.00%	21.00%
State income taxes, net of federal benefit	2.81%	3.21%	2.83%	3.20%
Excess tax benefit from stock-based compensation arrangements	(0.24%)	0.09%	(0.44%)	0.20%
Change in cash surrender value of life insurance	(0.90%)	(0.45%)	(0.56%)	(0.70%)
Tax credits	(2.54%)	(1.51%)	(2.62%)	(1.10%)
Tax exempt interest income	(0.33%)	(0.45%)	(0.34%)	(0.50%)
Other, net	0.97%	(0.14%)	0.55%	(0.50%)
Effective tax rate	20.77%	21.75%	20.42%	21.60%