Note 5 - Earnings Per Share - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Net income	$ 77,199	$ 54,321	$ 150,583	$ 101,173
Basic weighted-average number of common shares outstanding (in shares)	79,167,004	79,581,097	79,347,886	79,584,587
Diluted weighted-average number of common shares outstanding (in shares)	79,418,668	79,682,426	79,624,344	79,756,226
Average restricted stock units with anti-dilutive effect (in shares)	19,170	126,084	44,996	86,741
Basic (in dollars per share)	$ 0.98	$ 0.68	$ 1.90	$ 1.27
Diluted (in dollars per share)	$ 0.97	$ 0.68	$ 1.89	$ 1.27
Restricted Stock Units (RSUs) [Member]
Dilutive effect of weighted-average outstanding common share equivalents RSUs (in shares)	251,664	101,329	276,458	171,639