Net Income (Loss) Per Share - Calculation of net loss per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator (both basic and diluted)
Net income (loss) relevant to common stockholders	$ 21,965	$ (13,598)	$ 2,535	$ (35,830)
Denominator
Denominator for basic earnings (loss) per share (in shares)	83,040	52,975	74,124	42,526
Denominator for diluted income (loss) per share (in shares)	86,264	52,975	77,118	42,526
Basic income (loss) per common share (in dollars per share)	$ 0.26	$ (0.26)	$ 0.03	$ (0.84)
Diluted income (loss) per common share (in dollars per share)	$ 0.25	$ (0.26)	$ 0.03	$ (0.84)
Stock options
Denominator
Dilutive effect of share based payment (in shares)	2,808	0	2,822	0
Performance stock units
Denominator
Dilutive effect of share based payment (in shares)	37	0	0	0
Restricted Stock Units (RSUs)
Denominator
Dilutive effect of share based payment (in shares)	379	0	172	0

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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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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