Note 13 - Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unrecognized tax benefits at beginning of period	$ 2,401	$ 2,332	$ 2,087
Gross increases – tax positions in current year	619	429	692
Gross increases – tax positions in a prior year
Reductions due to lapse of statute of limitations	(465)	(360)	(447)
Unrecognized tax benefits at end of period	$ 2,555	$ 2,401	$ 2,332