Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Currency Translation Adjustments and Other
Beginning balance	$ (206,610)	$ (136,020)	$ (36,087)
Changes in cumulative translation adjustment and other	66,172	(70,590)	(99,933)
Ending balance	(140,438)	(206,610)	(136,020)
Net Actuarial Loss
Beginning balance	(620,292)	(576,993)	(585,941)
Amortization	20,267	18,876	19,505
Other current period change	39,872	(62,175)	(10,557)
Ending balance	(560,153)	(620,292)	(576,993)
Prior Service Credit
Beginning balance	(7,130)	278	1,758
Amortization	219	165	(1,411)
Other current period change	1	(7,573)	(69)
Ending balance	(6,910)	(7,130)	278
Accumulated Other Comprehensive Loss
Beginning balance	(834,032)	(712,735)	(620,270)
Amortization	20,486	19,041	18,094
Other current period change	106,045	(140,338)	(110,559)
Ending balance	$ (707,501)	$ (834,032)	$ (712,735)