Earnings (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net earnings (loss)	$ 94,455	$ 7,323	$ 13,753	$ (19,843)	$ 101,778	$ (6,090)
Weighted average shares outstanding	54,153		53,450		54,042	53,428
Effect of dilutive stock awards	1,553		845		1,559	0
Weighted-average dilutive shares	55,706		54,295		55,601	53,428
Basic earnings (loss) per common share	$ 1.74		$ 0.26		$ 1.88	$ (0.11)
Diluted earnings (loss) per common share	$ 1.70		$ 0.25		$ 1.83	$ (0.11)
Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options	0		0		0	797
Performance-based restricted stock units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options	263		222		263	1,172
Share-based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options	1,107		2,411		1,123	2,801

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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