Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (61,662)	$ (131,845)	$ (111,581)
Other comprehensive loss, net of tax :
Change in foreign currency translation adjustments	8	10
Pension benefit plan	532	(388)	(1,505)
Total comprehensive loss	$ (61,122)	$ (132,223)	$ (113,086)