Note 6 - Earnings Per Share - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Net income	$ 82,371	$ 99,035	$ 271,598	$ 263,041
Basic weighted-average number of common shares outstanding (in shares)	72,568,518	73,956,052	72,546,149	74,743,941
Dilutive effect of weighted-average outstanding common share equivalents RSUs (in shares)	321,896	286,000	301,758	324,291
Diluted weighted-average number of common shares outstanding (in shares)	72,890,414	74,242,052	72,847,907	75,068,232
Average restricted stock units with anti-dilutive effect (in shares)	0	13,534	2,098	48,073
Basic (in dollars per share)	$ 1.14	$ 1.34	$ 3.74	$ 3.52
Diluted (in dollars per share)	$ 1.13	$ 1.33	$ 3.73	$ 3.5