Note 5 - Earnings Per Share - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net income	$ 72,835	$ 69,757	$ 211,758	$ 207,237
Weighted-average shares:
Basic weighted-average number of common shares outstanding (in shares)	79,736,814	81,311,899	80,096,855	81,224,555
Diluted (in shares)	79,993,830	81,855,271	80,330,616	81,770,874
Average stock options and restricted stock units with anti-dilutive effect (in shares)	32,321	1,854	47,690	15,625
Basic (in dollars per share)	$ 0.91	$ 0.86	$ 2.64	$ 2.55
Diluted (in dollars per share)	$ 0.91	$ 0.85	$ 2.64	$ 2.53
Warrant [Member]
Weighted-average shares:
Dilutive effect of weighted-average outstanding common share equivalents (in shares)	0	234,105	0	268,988
Restricted Stock Units (RSUs) [Member]
Weighted-average shares:
Dilutive effect of weighted-average outstanding common share equivalents (in shares)	257,016	309,267	233,761	277,331