Note 9 - Income Taxes - Difference Between Statutory and Effective Tax Rates (Details)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
U.S. federal statutory income tax rate	21.00%	21.00%	21.00%
State income taxes, net of federal benefit	2.75%	3.27%	3.45%
Excess tax benefits from stock-based compensation arrangements	(0.76%)	(0.31%)	(0.97%)
Change in cash surrender value of life insurance	(0.61%)	(0.64%)	0.18%
Tax credits	(1.54%)	(0.54%)	(0.16%)
Tax exempt interest income	(0.43%)	(0.50%)	(0.62%)
Non-deductible merger expenses	0.00%	0.00%	0.11%
Insurance captive	0.00%	(0.20%)	(0.29%)
Amortization of investment in tax credit partnerships	0.00%	0.20%	0.06%
Other, net	0.25%	(0.40%)	(0.19%)
Effective tax rate	20.66%	21.88%	22.57%