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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net income	$ 55,566	$ 29,528	$ 121,488	$ 76,402
Denominator:
Weighted-average outstanding shares - basic (in shares)	44,970	43,308	44,737	43,055
Effect of dilutive securities (in shares)	1,985	2,525	2,082	2,461
Weighted-average outstanding shares - diluted (in shares)	46,955	45,833	46,819	45,516
Net income per share:
Earnings per share, basic (in dollars per share)	$ 1.24	$ 0.68	$ 2.72	$ 1.77
Earnings per share, diluted (in dollars per share)	$ 1.18	$ 0.64	$ 2.59	$ 1.68