Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net loss	$ (43,129)	$ (23,705)	$ (22,333)
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustment	5,131	(2,107)	1,574
Defined benefit plans, net of tax:
Actuarial gain (loss) on benefit obligations and plan assets, net of tax provision of $401 and $603 and tax benefit of $531 for the years ended December 31, 2017, 2016 and 2015, respectively	1,424	2,298	(1,862)
Amortization of deferred loss, net of tax provision of $48 and $10 for the years ended December 31, 2016 and 2015, respectively	0	195	35
Amortization of prior service cost, net of tax provision of $30, $30 and $30 for the years ended December 31, 2017, 2016 and 2015, respectively	121	120	106
Settlements and plan changes, net of tax provision of $91 for the year ended December 31, 2015	0	0	318
Other comprehensive income, net of tax	6,676	506	171
Comprehensive loss	$ (36,453)	$ (23,199)	$ (22,162)