Accumulated Other Comprehensive Income (Loss) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2016	$ (81,782)
Other comprehensive (loss) income before reclassifications	(1,670)
Amounts reclassified from AOCI	12,205
Balance at September 30, 2017	(71,247)
Pension and Other Post-Retirement Benefit Items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2016	(64,883)
Other comprehensive (loss) income before reclassifications	(442)
Amounts reclassified from AOCI	(120)
Balance at September 30, 2017	(65,445)
Marketable Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2016	3,075
Other comprehensive (loss) income before reclassifications	(95)
Amounts reclassified from AOCI	(2,980)
Balance at September 30, 2017	0
Cash Flow Hedging Instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2016	0
Other comprehensive (loss) income before reclassifications	(6,126)
Amounts reclassified from AOCI	2,540
Balance at September 30, 2017	(3,586)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2016	(19,974)
Other comprehensive (loss) income before reclassifications	4,993
Amounts reclassified from AOCI	12,765
Balance at September 30, 2017	$ (2,216)