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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Net income	$ 55,169	$ 30,167	$ 100,582	$ 65,922
Weighted-average outstanding shares - basic (in shares)	45,796	44,785	45,647	44,620
Effect of dilutive securities (in shares)	1,958	2,046	2,085	2,130
Weighted-average outstanding shares - diluted (in shares)	47,754	46,831	47,732	46,750
Earnings per share, basic (in dollars per share)	$ 1.20	$ 0.67	$ 2.20	$ 1.48
Earnings per share, diluted (in dollars per share)	$ 1.16	$ 0.64	$ 2.11	$ 1.41