Note 5 - Earnings Per Share - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net income	$ 72,397	$ 56,794	$ 222,980	$ 157,967
Basic weighted-average number of common shares outstanding (in shares)	77,846,424	79,628,372	78,841,899	79,599,288
Dilutive effect of weighted-average outstanding common share equivalents RSUs (in shares)	306,984	135,946	286,745	159,655
Diluted weighted-average number of common shares outstanding (in shares)	78,153,408	79,764,318	79,128,644	79,758,943
Average restricted stock units with anti-dilutive effect (in shares)	884	117,621	30,130	97,110
Basic (in dollars per share)	$ 0.93	$ 0.71	$ 2.83	$ 1.98
Diluted (in dollars per share)	$ 0.93	$ 0.71	$ 2.82	$ 1.98