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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net income	$ 30,167	$ 20,693	$ 65,922	$ 46,874
Denominator:
Weighted-average outstanding shares - basic (in shares)	44,785	43,109	44,620	42,929
Effect of dilutive securities (in shares)	2,046	2,374	2,130	2,429
Weighted-average outstanding shares - diluted (in shares)	46,831	45,483	46,750	45,358
Net income per share:
Earnings per share, basic (in dollars per share)	$ 0.67	$ 0.48	$ 1.48	$ 1.09
Earnings per share, diluted (in dollars per share)	$ 0.64	$ 0.45	$ 1.41	$ 1.03