Accumulated Other Comprehensive (Loss) Income Accumulated Other Comprehensive (Loss) Income - Activity in AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 642,817	$ (172,338)	$ (186,924)	$ (149,455)
Other comprehensive (loss) income	(2,253)	1,401	(7,212)	6,115
Ending balance	731,003	(187,338)	731,003	(187,338)
Accumulated other comprehensive loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(5,189)	(5,830)	(230)	(10,544)
Ending balance	(7,442)	(4,429)	(7,442)	(4,429)
Pension and other postretirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(6,129)	(11,652)	(7,126)	(12,880)
Other comprehensive (loss) income	618	487	1,615	1,715
Ending balance	(5,511)	(11,165)	(5,511)	(11,165)
Pension and other postretirement benefits, gain (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive (loss) income, before reclassifications, before tax	614	434	1,592	1,556
Other comprehensive (loss) income, before reclassifications, tax	0	0	0	0
Other comprehensive (loss) income, before reclassifications	614	434	1,592	1,556
Pension and other postretirement benefits, prior service cost
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amortization of prior service cost	4	53	23	159
Less: Tax expense	0	0	0	0
Net amount reclassified from AOCI to net income/loss	4	53	23	159
Foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	2,122	7,504	8,318	3,874
(Loss) gain on foreign currency translation	(2,953)	709	(9,149)	4,339
Less: Tax expense/(Tax benefit)	0	0	0	0
Other comprehensive (loss) income	(2,953)	709	(9,149)	4,339
Ending balance	(831)	8,213	(831)	8,213
Cash flow hedge derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,182)	(1,682)	(1,422)	(1,538)
Other comprehensive (loss) income, before reclassifications, before tax	(76)	(112)	(464)	(1,074)
Other comprehensive (loss) income, before reclassifications, tax	128	88	173	22
Other comprehensive (loss) income, before reclassifications	(204)	(200)	(637)	(1,096)
Net amount reclassified from AOCI to net income/loss	286	405	959	1,157
Ending balance	$ (1,100)	$ (1,477)	$ (1,100)	$ (1,477)