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
	Mar. 31, 2017	Mar. 31, 2016
Numerator:
Net income	$ 14,477	$ 10,575
Denominator:
Weighted-average shares outstanding, basic (in shares)	41,047	40,028
Effect of dilutive securities (in shares)	2,221	1,618
Weighted-average shares outstanding, diluted (in shares)	43,268	41,646
Net income per share:
Earnings per share, basic (in dollars per share)	$ 0.35	$ 0.26
Earnings per share, diluted (in dollars per share)	$ 0.33	$ 0.25