Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (11,302)	$ (10,118)	$ (20,507)	$ (20,517)
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustment	(3,404)	2,814	(1,967)	4,126
Defined benefit plans, net of tax:
Amortization of prior service cost, net of tax provision of $5 and $8 for the three months ended June 30, 2018 and 2017, respectively; net of tax provision of $10 and $15 for the six months ended June 30, 2018 and 2017, respectively	19	31	38	60
Other comprehensive income (loss), net of tax	(3,385)	2,845	(1,929)	4,186
Comprehensive loss	$ (14,687)	$ (7,273)	$ (22,436)	$ (16,331)