Note 8 - Income Taxes - Difference Between Statutory and Effective Tax Rates (Details)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
U.S. federal statutory income tax rate	21.00%	21.00%
State income taxes, net of federal benefit	3.30%	3.20%
Excess tax benefit from stock-based compensation arrangements	(5.90%)	(3.00%)
Change in cash surrender value of life insurance	1.80%	(0.40%)
Tax credits	(1.70%)	(0.50%)
Tax exempt interest income	(1.60%)	(0.10%)
Non-deductible merger expenses	1.10%	0.00%
Insurance captive	(0.90%)	0.00%
Other, net	(1.70%)	(0.80%)
Effective tax rate	15.40%	19.40%