Note 5 - Earnings Per Share - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net income	$ 69,757	$ 49,746	$ 207,237	$ 150,102
Weighted-average shares:
Basic weighted-average number of common shares outstanding (in shares)	81,311,899	80,665,398	81,224,555	80,073,249
Dilutive effect of weighted-average outstanding common share equivalents
Diluted weighted-average number of common shares outstanding (in shares)	81,855,271	81,404,854	81,770,874	80,797,179
Average stock options and restricted stock units with anti-dilutive effect (in shares)	1,854		15,625	6,561
Basic (in dollars per share)	$ 0.86	$ 0.62	$ 2.55	$ 1.87
Diluted (in dollars per share)	$ 0.85	$ 0.61	$ 2.53	$ 1.86
Warrant [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Warrants (in shares)	234,105	399,957	268,988	409,019
Employee Stock Option [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Warrants (in shares)		19,221		25,706
Restricted Stock Units (RSUs) [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Warrants (in shares)	309,267	320,278	277,331	289,205