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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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net earnings	$ 40,491	$ 31,277	$ 94,455	$ 7,323	$ 1,664	$ 12,918	$ 13,753	$ (19,843)	$ 173,546	$ 8,492	$ 6,653
Weighted-average shares outstanding									54,325	53,471	53,282
Effect of dilutive stock awards									1,630	1,071	562
Weighted-average dilutive shares									55,955	54,542	53,844
Basic earnings per common share	$ 0.74	$ 0.57	$ 1.74	$ 0.14	$ 0.03	$ 0.24	$ 0.26	$ (0.37)	$ 3.19	$ 0.16	$ 0.12
Diluted earnings per common share	$ 0.72	$ 0.56	$ 1.70	$ 0.13	$ 0.03	$ 0.24	$ 0.25	$ (0.37)	$ 3.10	$ 0.16	$ 0.12
Restricted share units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from diluted earnings per common share									0	0	0
Performance share units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from diluted earnings per common share									290	200	329
Stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from diluted earnings per common share									1,109	1,498	2,554