Note 7 - Income Taxes - Difference Between Statutory and Effective Tax Rates (Details)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
U.S. federal statutory income tax rate	21.00%	21.00%
State income taxes, net of federal benefit	3.30%	3.30%
Excess tax benefit from stock-based compensation arrangements	0.30%	(1.10%)
Change in cash surrender value of life insurance	(1.00%)	(0.70%)
Adoption of ASU 2023-02	(1.30%)	0.00%
Tax credits	0.60%	0.40%
Tax exempt interest income	(0.50%)	(0.50%)
Insurance captive	0.00%	(0.30%)
Other, net	(0.90%)	(0.20%)
Effective tax rate	21.50%	21.90%