Note 7 - Income Taxes - Difference Between Statutory and Effective Tax Rates (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
U.S. federal statutory income tax rate	21.00%	21.00%	21.00%	21.00%
State income taxes, net of federal benefit	3.60%	3.50%	3.50%	3.50%
Excess tax benefit from stock-based compensation arrangements	0.20%	(1.60%)	(0.50%)	(2.40%)
Change in cash surrender value of life insurance	(0.60%)	0.90%	(0.70%)	1.10%
Tax credits	(1.20%)	(0.50%)	(0.40%)	(0.70%)
Tax exempt interest income	(0.50%)	(0.60%)	(0.50%)	(0.80%)
Non-deductible merger expenses	0.00%	0.10%	0.00%	0.30%
Insurance captive	(0.30%)	(0.20%)	(0.30%)	(0.40%)
Other, net	0.20%	(0.70%)	0.00%	(1.10%)
Effective tax rate	22.40%	21.90%	22.10%	20.50%