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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net income	$ 10,602	$ 10,109	$ 21,393	$ 19,944
Basic (in shares)	22,783	22,336	22,788	22,295
Dilutive securities (in shares)	458	368	483	363
Average shares outstanding including dilutive securities including dilutive securities (in shares)	23,241	22,704	23,271	22,658
Basic (in dollars per share)	$ 0.47	$ 0.45	$ 0.94	$ 0.89
Diluted (in dollars per share)	$ 0.46	$ 0.45	$ 0.92	$ 0.88