Note 6 - Earnings Per Share - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Net income	$ 99,035	$ 72,397	$ 263,041	$ 222,980
Basic weighted-average number of common shares outstanding (in shares)	73,158,096	77,846,424	74,475,032	78,841,899
Dilutive effect of weighted-average outstanding common share equivalents RSUs (in shares)	286,000	306,984	324,292	286,745
Diluted weighted-average number of common shares outstanding (in shares)	73,444,096	78,153,408	74,799,324	79,128,644
Average restricted stock units with anti-dilutive effect (in shares)	0	884	0	30,130
Basic (in dollars per share)	$ 1.35	$ 0.93	$ 3.53	$ 2.83
Diluted (in dollars per share)	$ 1.35	$ 0.93	$ 3.52	$ 2.82