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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net income	$ 20,693	$ 24,206	$ 46,874	$ 46,062
Weighted-average shares outstanding, basic (in shares)	43,109	42,237	42,929	42,079
Effect of dilutive securities (in shares)	2,374	2,163	2,429	2,262
Weighted-average shares outstanding, diluted (in shares)	45,483	44,400	45,358	44,341
Earnings per share, basic (in dollars per share)	$ 0.48	$ 0.57	$ 1.09	$ 1.09
Earnings per share, diluted (in dollars per share)	$ 0.45	$ 0.55	$ 1.03	$ 1.04