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		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Numerator:
Net income	$ 14,373	$ 11,201	$ 36,146	$ 25,063
Denominator:
Weighted-average outstanding shares used to compute basic net income per share (in shares)	40,590	39,592	40,335	39,422
Effect of dilutive securities (in shares)	1,305	1,097	1,417	1,254
Weighted-average outstanding shares used to compute diluted net income per share (in shares)	41,895	40,689	41,752	40,676
Basic (in dollars per share)	$ 0.35	$ 0.28	$ 0.90	$ 0.64
Diluted (in dollars per share)	$ 0.34	$ 0.28	$ 0.87	$ 0.62