Note 11 - Net Income Per Share - Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net income	$ 13,579	$ 10,602	$ 26,983	$ 21,393
Basic (in shares)	22,625	22,538	22,601	22,515
Dilutive securities (in shares)	354	458	374	483
Average shares outstanding including dilutive securities including dilutive securities (in shares)	22,979	22,996	22,975	22,998
Basic (in dollars per share)	$ 0.60	$ 0.47	$ 1.19	$ 0.95
Diluted (in dollars per share)	$ 0.59	$ 0.46	$ 1.17	$ 0.93