Note 8 - Income Taxes - Difference Between Statutory and Effective Tax Rates (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
U.S. federal statutory income tax rate	21.00%	21.00%	21.00%	21.00%
State income taxes, net of federal benefit	3.60%	3.50%	3.50%	3.40%
Excess tax benefit from stock-based compensation arrangements	0.00%	(0.10%)	(1.30%)	(1.70%)
Change in cash surrender value of life insurance	0.00%	(0.20%)	0.60%	(0.70%)
Tax credits	(0.50%)	(1.10%)	(0.60%)	(0.80%)
Tax exempt interest income	(0.50%)	(0.40%)	(0.70%)	(0.30%)
Non-deductible merger expenses	0.00%	0.10%	0.20%	0.50%
Insurance captive	(0.30%)	(0.30%)	(0.30%)	(0.20%)
Other, net	0.70%	0.50%	(0.30%)	(0.30%)
Effective tax rate	24.00%	23.00%	22.10%	20.90%