Note 6 - 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, 2020	Mar. 31, 2019
Numerator:
Net income	$ 35,756	$ 26,181
Denominator:
Weighted-average outstanding shares - basic (in shares)	44,455	42,749
Effect of dilutive securities (in shares)	2,215	2,483
Weighted-average outstanding shares - diluted (in shares)	46,670	45,232
Net income per share:
Earnings per share, basic (in dollars per share)	$ 0.80	$ 0.61
Earnings per share, diluted (in dollars per share)	$ 0.77	$ 0.58