Note 4 - Earnings Per Share - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net income	$ 51,415	$ 34,831	$ 100,356	$ 80,994
Weighted-average shares:
Basic weighted-average number of common shares outstanding (in shares)	79,840,188	78,846,237	79,772,268	79,290,378
Dilutive effect of weighted-average outstanding common share equivalents
Diluted weighted-average number of common shares outstanding (in shares)	80,562,607	79,619,883	80,488,306	80,006,866
Average stock options and warrants with anti-dilutive effect (in shares)	0	177,642	9,895	268,593
Basic (in dollars per share)	$ 0.64	$ 0.44	$ 1.26	$ 1.02
Diluted (in dollars per share)	$ 0.64	$ 0.44	$ 1.25	$ 1.01
Warrant [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Warrants (in shares)	410,677	539,201	413,626	495,785
Employee Stock Option [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Warrants (in shares)	24,169	92,455	29,002	87,737
Restricted Stock Units (RSUs) [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Warrants (in shares)	287,573	141,990	273,410	132,966

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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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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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