Note 5 - Net Income Per Share - Net Income Per Share Basic and Diluted (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
Numerator:
Net income	$ 15,014	$ 11,198	$ 29,490	$ 21,773
Denominator:
Weighted-average shares outstanding, basic (in shares)	41,323	40,387	41,185	40,208
Effect of dilutive securities (in shares)	2,074	1,329	2,147	1,473
Weighted-average shares outstanding, diluted (in shares)	43,397	41,716	43,332	41,681
Net income per share:
Earnings per share, basic (in dollars per share)	$ 0.36	$ 0.28	$ 0.72	$ 0.54
Earnings per share, diluted (in dollars per share)	$ 0.35	$ 0.27	$ 0.68	$ 0.52