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, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Net income	$ 99,504	$ 114,679	$ 209,306	$ 194,245
Weighted-average outstanding shares - basic (in shares)	47,489	46,675	47,361	46,550
Effect of dilutive securities (in shares)	1,267	1,611	1,344	1,718
Weighted-average outstanding shares - diluted (in shares)	48,756	48,286	48,705	48,268
Earnings per share, basic (in dollars per share)	$ 2.10	$ 2.46	$ 4.42	$ 4.17
Earnings per share, diluted (in dollars per share)	$ 2.04	$ 2.37	$ 4.30	$ 4.02