Note 7 - Income Taxes - Difference Between Statutory and Effective Tax Rates (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
U.S. federal statutory income tax rate	21.00%	21.00%	21.00%	21.00%
State income taxes, net of federal benefit	2.91%	3.27%	3.12%	3.42%
Excess tax benefit from stock-based compensation arrangements	(1.38%)	0.12%	(0.36%)	(0.29%)
Change in cash surrender value of life insurance	(0.79%)	(0.08%)	(0.73%)	(0.49%)
Tax credits	(0.52%)	(0.71%)	(0.90%)	(0.48%)
Tax exempt interest income	(0.42%)	(0.48%)	(0.45%)	(0.49%)
Insurance captive	0.00%	(0.19%)	0.00%	(0.27%)
Other, net	(0.15%)	(0.93%)	(0.41%)	(0.32%)
Effective tax rate	20.65%	22.00%	21.27%	22.08%