Note 7 - 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, 2019	Mar. 31, 2018
Net income	$ 26,181	$ 21,856
Weighted-average shares outstanding, basic (in shares)	42,749	41,922
Effect of dilutive securities (in shares)	2,483	2,360
Weighted-average shares outstanding, diluted (in shares)	45,232	44,282
Earnings per share, basic (in dollars per share)	$ 0.61	$ 0.52
Earnings per share, diluted (in dollars per share)	$ 0.58	$ 0.49