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Earnings Per Common Share Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net earnings (loss)	$ 1,664	$ 12,918	$ 13,753	$ (19,843)	$ 34,824	$ (12,599)	$ (8,893)	$ (6,679)	$ 8,492	$ 6,653	$ (105,195)
Weighted-average shares outstanding									53,471	53,282	53,121
Effect of dilutive stock awards									1,071	562	0
Weighted-average dilutive shares									54,542	53,844	53,121
Basic earnings (loss) per common share	$ 0.03	$ 0.24	$ 0.26	$ (0.37)	$ 0.65	$ (0.24)	$ (0.17)	$ (0.13)	$ 0.16	$ 0.12	$ (1.98)
Diluted earnings (loss) per common share	$ 0.03	$ 0.24	$ 0.25	$ (0.37)	$ 0.65	$ (0.24)	$ (0.17)	$ (0.13)	$ 0.16	$ 0.12	$ (1.98)
Restricted share units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from diluted earnings (loss per common share									0	0	482
Performance share units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from diluted earnings (loss per common share									200	329	880
Stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from diluted earnings (loss per common share									1,498	2,554	3,072