Note 7 - Income Taxes - Difference Between Statutory and Effective Tax Rates (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
U.S. federal statutory income tax rate	21.00%	21.00%	21.00%	21.00%
State income taxes, net of federal benefit	3.30%	3.60%	3.40%	3.50%
Excess tax benefit from stock-based compensation arrangements	0.10%	0.00%	(0.30%)	(1.30%)
Change in cash surrender value of life insurance	(0.10%)	0.00%	(0.50%)	0.60%
Tax credits	(0.70%)	(0.50%)	(0.50%)	(0.60%)
Tax exempt interest income	(0.50%)	(0.50%)	(0.50%)	(0.70%)
Non-deductible merger expenses	0.00%	0.00%	0.00%	0.20%
Insurance captive	(0.20%)	(0.30%)	(0.30%)	(0.30%)
Other, net	(0.90%)	0.70%	(0.20%)	(0.30%)
Effective tax rate	22.00%	24.00%	22.10%	22.10%