CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (12,150)	$ (20,724)	$ (63,559)
Other comprehensive income (loss), net of tax:
Change in foreign currency translation adjustments	(261)	10	27
Pension benefit plan	(81)	5	(84)
Total comprehensive income (loss)	$ (12,492)	$ (20,709)	$ (63,616)

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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