Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ (94,652)	$ (131,327)	$ (69,140)
Other comprehensive income before reclassifications	110,430	(67,320)	(66,440)
Tax effect	3,714	9,486	(3,670)
Other comprehensive income before reclassifications, net of tax	114,144	(57,834)	(70,110)
Amounts reclassified out of AOCI	8,330	91,014	12,189
Tax effect	(2,108)	3,495	(4,266)
Amounts reclassified out of AOCI, net of tax	6,222	94,509	7,923
Other comprehensive income (loss)	120,366	36,675	(62,187)
Ending Balance	25,714	(94,652)	(131,327)
Pension and Other Post-Retirement Actuarial Items [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(64,496)	(136,422)	(155,760)
Other comprehensive income before reclassifications	(15,671)	(32,398)	15,169
Tax effect	4,373	9,815	(4,196)
Other comprehensive income before reclassifications, net of tax	(11,298)	(22,583)	10,973
Amounts reclassified out of AOCI	9,147	91,014	12,869
Tax effect	(2,394)	3,495	(4,504)
Amounts reclassified out of AOCI, net of tax	6,753	94,509	8,365
Other comprehensive income (loss)	(4,545)	71,926	19,338
Ending Balance	(69,041)	(64,496)	(136,422)
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(31,266)	4,597	84,703
Other comprehensive income before reclassifications	124,220	(35,863)	(80,106)
Tax effect	0	0	0
Other comprehensive income before reclassifications, net of tax	124,220	(35,863)	(80,106)
Amounts reclassified out of AOCI	0	0	0
Tax effect	0	0	0
Amounts reclassified out of AOCI, net of tax	0	0	0
Other comprehensive income (loss)	124,220	(35,863)	(80,106)
Ending Balance	92,954	(31,266)	4,597
Unrealized Gain (Loss) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	1,110	498	1,917
Other comprehensive income before reclassifications	1,881	941	(1,503)
Tax effect	(659)	(329)	526
Other comprehensive income before reclassifications, net of tax	1,222	612	(977)
Amounts reclassified out of AOCI	(817)	0	(680)
Tax effect	286	0	238
Amounts reclassified out of AOCI, net of tax	(531)	0	(442)
Other comprehensive income (loss)	691	612	(1,419)
Ending Balance	$ 1,801	$ 1,110	$ 498