Note 8 - Income Taxes - Difference Between Statutory and Effective Tax Rates (Details)	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
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	(1.10%)	(5.90%)
Change in cash surrender value of life insurance	(0.70%)	1.80%
Tax credits	0.40%	1.70%
Tax credits	(0.40%)	(1.70%)
Tax exempt interest income	(0.50%)	(1.60%)
Non-deductible merger expenses	0.00%	1.10%
Insurance captive	(0.30%)	(0.90%)
Other, net	(0.20%)	(1.70%)
Effective tax rate	21.90%	15.40%