Note 10 - Income Taxes - Difference Between Statutory and Effective Tax Rates (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
U.S. federal statutory income tax rate	21.00%	21.00%	21.00%
State income taxes, net of federal benefit	3.30%	3.50%	3.50%
Excess tax benefits from stock-based compensation arrangements	(0.30%)	(1.00%)	(1.10%)
Change in cash surrender value of life insurance	(0.70%)	0.20%	(0.80%)
Tax credits	(0.50%)	(0.20%)	(0.30%)
Tax exempt interest income	(0.50%)	(0.60%)	(0.40%)
Non-deductible merger expenses	0.00%	0.10%	0.40%
Insurance captive	(0.20%)	(0.30%)	(0.20%)
Amortization of investment in tax credit partnerships	0.20%	0.10%	0.10%
Other, net	(0.40%)	(0.20%)	(0.40%)
Effective tax rate	21.90%	22.60%	21.80%