Note 10 - Income Taxes - Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Currently payable										$ 6,502	$ 5,556	$ 3,662
Revaluation of deferred income taxes resulting from change in statutory tax rates	$ 5,900									5,869
Deferred										270	885	1,631
Total income tax expense	$ 7,567	[1]	$ 2,076	$ 1,722	$ 1,276	$ 931	$ 1,560	$ 1,235	$ 2,715	$ 12,641	$ 6,441	$ 5,293

[1] Income tax expense includes $5.9 million related to the remeasurement of the Company's net deferred tax assets due to the change in Federal tax rates.