Accumulated Other Comprehensive Income (Loss) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2016	$ (81,782)
Other comprehensive income (loss) before reclassifications	987
Amounts reclassified from AOCI	6,656
Balance at March 31, 2017	(74,139)
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 income (loss) before reclassifications	0
Amounts reclassified from AOCI	(44)
Balance at March 31, 2017	(64,927)
Marketable Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2016	3,075
Other comprehensive income (loss) before reclassifications	(94)
Amounts reclassified from AOCI	(3,042)
Balance at March 31, 2017	(61)
Cash Flow Hedging Instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2016	0
Other comprehensive income (loss) before reclassifications	(2,088)
Amounts reclassified from AOCI	788
Balance at March 31, 2017	(1,300)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2016	(19,974)
Other comprehensive income (loss) before reclassifications	3,169
Amounts reclassified from AOCI	8,954
Balance at March 31, 2017	$ (7,851)