Note 5 - Earnings Per Share - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net income	$ 73,664	$ 51,415	$ 137,480	$ 100,356
Weighted-average shares:
Basic weighted-average number of common shares outstanding (in shares)	81,236,315	79,840,188	81,180,160	79,772,268
Dilutive effect of weighted-average outstanding common share equivalents
Diluted weighted-average number of common shares outstanding (in shares)	81,774,986	80,562,607	81,727,977	80,488,305
Average stock options and restricted stock units with anti-dilutive effect (in shares)	6,521		22,624	9,895
Basic (in dollars per share)	$ 0.91	$ 0.64	$ 1.69	$ 1.26
Diluted (in dollars per share)	$ 0.90	$ 0.64	$ 1.68	$ 1.25
Warrant [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Warrants (in shares)	278,080	410,677	286,718	413,625
Employee Stock Option [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Warrants (in shares)		24,169		29,002
Restricted Stock Units (RSUs) [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Warrants (in shares)	260,591	287,573	261,099	273,410

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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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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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