Note 6 - Income Taxes (Details Textual) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 5,786	$ 5,812
Effective Income Tax Rate Reconciliation, Percent	19.30%	21.60%
Effective income tax rate excluding the favorable effects of TCJA, Percent	30.30%
Effective income tax rate excluding impact of effect of share based compensation, Percent		31.40%
Provisional Toll Charge			$ 2,105