Note 7 - Income Taxes - Difference Between Statutory and Effective Tax Rates (Details)	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
U.S. federal statutory income tax rate	21.00%	21.00%
State income taxes, net of federal benefit	2.84%	3.27%
Excess tax benefit from stock-based compensation arrangements	(0.65%)	0.32%
Change in cash surrender value of life insurance	(0.22%)	(0.96%)
Tax credits	(2.70%)	(0.69%)
Tax exempt interest income	(0.34%)	(0.49%)
Adoption of ASU 2023-02	0.00%	(1.28%)
Other, net	0.13%	0.28%
Effective tax rate	20.06%	21.45%