Note 5 - Earnings Per Share - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Net income	$ 63,816	$ 48,941
Weighted-average shares:
Basic weighted-average number of common shares outstanding (in shares)	81,123,380	79,703,593
Dilutive effect of weighted-average outstanding common share equivalents
Diluted weighted-average number of common shares outstanding (in shares)	81,680,445	80,413,178
Average stock options and restricted stock units with anti-dilutive effect (in shares)	38,906	19,900
Basic (in dollars per share)	$ 0.79	$ 0.61
Diluted (in dollars per share)	$ 0.78	$ 0.61
Warrant [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Warrants (in shares)	295,453	416,607
Employee Stock Option [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Warrants (in shares)		33,888
Restricted Stock Units (RSUs) [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Warrants (in shares)	261,612	259,090

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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