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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net income	$ 29,528	$ 31,568	$ 76,402	$ 77,630
Denominator:
Weighted-average outstanding shares - basic (in shares)	43,308	42,362	43,055	42,173
Effect of dilutive securities (in shares)	2,525	2,307	2,461	2,277
Weighted-average outstanding shares - diluted (in shares)	45,833	44,669	45,516	44,450
Net income per share:
Earnings per share, basic (in dollars per share)	$ 0.68	$ 0.75	$ 1.77	$ 1.84
Earnings per share, diluted (in dollars per share)	$ 0.64	$ 0.71	$ 1.68	$ 1.75