Note 6 - Earnings Per Share - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Net income	$ 75,028	$ 73,384
Basic weighted-average number of common shares outstanding (in shares)	75,331,976	79,530,777
Dilutive effect of weighted-average outstanding common share equivalents RSUs (in shares)	387,399	301,528
Diluted weighted-average number of common shares outstanding (in shares)	75,719,375	79,832,305
Average restricted stock units with anti-dilutive effect (in shares)	22,574	71,108
Basic (in dollars per share)	$ 1.00	$ 0.92
Diluted (in dollars per share)	$ 0.99	$ 0.92