Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ (156,393)
Other comprehensive income (loss)		40,579	$ (16,255)	$ (13,877)
Ending balance		(115,814)	(156,393)
Foreign currency translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(34,896)	(22,625)
Other comprehensive income (loss), before reclassifications		27,840	(12,271)
Ending balance		(7,056)	(34,896)	(22,625)
Pension and other post-retirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	[1]	(121,448)	(117,455)
Other comprehensive income (loss)	[1]	12,688	(3,993)
Ending balance	[1]	(108,760)	(121,448)	(117,455)
Amortization of net loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification to net income	[1]	8,785	8,027
Reclassification from AOCI, tax		(5,304)	(4,849)
Change in net gain
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification to net income	[1]	3,903	(12,020)
Reclassification from AOCI, tax		(2,357)	7,261
Derivative instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	[2]	(49)	(58)
Other comprehensive income (loss), before reclassifications	[2]	121	(587)
Reclassification to net income	[2]	(70)	596
Other comprehensive income (loss)	[2]	51	9
Ending balance	[2]	2	(49)	$ (58)
OCI before reclassifications to net income, tax		(73)	354
Reclassification from AOCI, tax		$ 42	$ (360)

[1] These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see Note 13, Pension Plans for additional information)

[2] See Note 5, Derivative Financial Instruments, for additional information regarding the Company's derivative instruments.