Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (63,559)	$ (61,662)	$ (131,845)
Other comprehensive income (loss), net of tax :
Change in foreign currency translation adjustments	27	8	10
Pension benefit plan	(84)	532	(388)
Total comprehensive income (loss)	$ (63,616)	$ (61,122)	$ (132,223)