Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2015			$ (71,016)
Other comprehensive income	$ 2,684	$ (3,771)	7,132	$ (13,169)
Balance at September 30, 2016	(63,884)		(63,884)
Unrecognized Benefit Plan Gains and Losses
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2015			(57,391)
Other comprehensive income			3,539
Balance at September 30, 2016	(53,852)		(53,852)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2015			(15,764)
Other comprehensive income			2,002
Balance at September 30, 2016	(13,762)		(13,762)
Unrealized Holding Gain on Marketable Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2015			2,139
Other comprehensive income			1,591
Balance at September 30, 2016	$ 3,730		$ 3,730