CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Unaudited) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (97)	$ 5,096	$ (51,537)	$ (183,498)
Other comprehensive (loss) income, net of tax
Translation adjustments	(697)	1,092	(1,625)	1,477
Minimum pension liability adjustments	1,045	704	2,089	1,408
Cash flow hedge adjustments	485	(36)	1,976	32
Total other comprehensive income, net of tax	833	1,760	2,440	2,917
Comprehensive income (loss)	$ 736	$ 6,856	$ (49,097)	$ (180,581)

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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