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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net income	$ 68,770	$ 55,566	$ 169,352	$ 121,488
Weighted-average outstanding shares - basic (in shares)	45,970	44,970	45,754	44,737
Effect of dilutive securities (in shares)	1,882	1,985	2,018	2,082
Weighted-average outstanding shares - diluted (in shares)	47,852	46,955	47,772	46,819
Earnings per share, basic (in dollars per share)	$ 1.50	$ 1.24	$ 3.70	$ 2.72
Earnings per share, diluted (in dollars per share)	$ 1.44	$ 1.18	$ 3.55	$ 2.59