Note 6 - Income Taxes - Difference Between Statutory and Effective Tax Rates (Details)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
U.S. federal statutory income tax rate	21.00%	21.00%
Kentucky state income tax enactment	(7.30%)
Excess tax benefits from share-based compensation arrangements	(1.70%)	(1.90%)
Increase in cash surrender value of life insurance	(1.20%)	(0.40%)
Tax credits	(0.70%)	(0.40%)
Tax exempt interest income	(0.30%)	(0.50%)
State income taxes, net of federal benefit	0.70%	0.70%
Other, net
Effective income tax rate	10.50%	18.50%