Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2015			$ (71,016)
Other comprehensive (loss) income	$ 811	$ (3,063)	4,448	$ (9,398)
Balance at June 30, 2016	(66,568)		(66,568)
Unrecognized Benefit Plan Gains and Losses
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2015			(57,391)
Other comprehensive (loss) income			3,583
Balance at June 30, 2016	(53,808)		(53,808)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2015			(15,764)
Other comprehensive (loss) income			(133)
Balance at June 30, 2016	(15,897)		(15,897)
Unrealized Holding Gain on Marketable Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2015			2,139
Other comprehensive (loss) income			998
Balance at June 30, 2016	$ 3,137		$ 3,137