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
	Mar. 31, 2021	Mar. 31, 2020
Net income	$ 45,413	$ 35,756
Weighted-average outstanding shares - basic (in shares)	45,498	44,455
Effect of dilutive securities (in shares)	2,213	2,215
Weighted-average outstanding shares - diluted (in shares)	47,711	46,670
Earnings per share, basic (in dollars per share)	$ 1.00	$ 0.80
Earnings per share, diluted (in dollars per share)	$ 0.95	$ 0.77