Note 5 - Earnings Per Share - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Net income	$ 66,679	$ 63,816
Weighted-average shares:
Basic weighted-average number of common shares outstanding (in shares)	80,455,317	81,123,380
Diluted (in shares)	80,703,134	81,680,445
Average stock options and restricted stock units with anti-dilutive effect (in shares)	44,545	38,906
Basic (in dollars per share)	$ 0.83	$ 0.79
Diluted (in dollars per share)	$ 0.83	$ 0.78
Warrant [Member]
Weighted-average shares:
Dilutive effect of weighted-average outstanding common share equivalents (in shares)		295,453
Restricted Stock Units (RSUs) [Member]
Weighted-average shares:
Dilutive effect of weighted-average outstanding common share equivalents (in shares)	247,817	261,612

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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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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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