Loss Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net earnings (loss)	$ 13,753	$ (8,893)	$ (6,090)	$ (15,572)
Weighted average shares outstanding	53,450	53,292	53,428	53,255
Effect of dilutive stock awards	845	0	0	0
Weighted-average dilutive shares	54,295	53,292	53,428	53,255
Basic earnings (loss) per common share	$ 0.26	$ (0.17)	$ (0.11)	$ (0.29)
Diluted earnings (loss) per common share	$ 0.25	$ (0.17)	$ (0.11)	$ (0.29)
Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options	0	688	797	688
Performance-based restricted stock units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options	222	880	1,172	880
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options	2,411	3,251	2,801	3,251

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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