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, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Net income	$ 121,163	$ 124,337	$ 330,469	$ 318,582
Weighted-average outstanding shares - basic (in shares)	47,780	46,829	47,501	46,643
Effect of dilutive securities (in shares)	1,012	1,520	1,233	1,652
Weighted-average outstanding shares - diluted (in shares)	48,792	48,349	48,734	48,295
Earnings per share, basic (in dollars per share)	$ 2.54	$ 2.66	$ 6.96	$ 6.83
Earnings per share, diluted (in dollars per share)	$ 2.48	$ 2.57	$ 6.78	$ 6.6