Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive (Loss) by Component (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
AOCI Attributable to Parent [Roll Forward]
Beginning balance, January 1	$ 3,412,152
Other comprehensive income (loss) before reclassifications, net of tax	(105,068)	$ 80,177
Amounts reclassified from accumulated other comprehensive loss, net of tax	14,309	11,455
Total other comprehensive income	(90,759)	91,632
Ending balance, June 30	3,511,972
Pension and Other Post-Retirement Benefits [Member]
AOCI Attributable to Parent [Roll Forward]
Beginning balance, January 1	(568,957)	(609,080)
Other comprehensive income (loss) before reclassifications, net of tax	0	0
Amounts reclassified from accumulated other comprehensive loss, net of tax	14,309	11,455
Total other comprehensive income	14,309	11,455
Ending balance, June 30	(554,648)	(597,625)
Net Investment Hedge [Member]
AOCI Attributable to Parent [Roll Forward]
Beginning balance, January 1	(17,388)	0
Other comprehensive income (loss) before reclassifications, net of tax	16,045	0
Amounts reclassified from accumulated other comprehensive loss, net of tax	0	0
Total other comprehensive income	16,045	0
Ending balance, June 30	(1,343)	0
Foreign Currency Translation [Member]
AOCI Attributable to Parent [Roll Forward]
Beginning balance, January 1	(266,247)	(403,941)
Other comprehensive income (loss) before reclassifications, net of tax	(121,113)	80,177
Amounts reclassified from accumulated other comprehensive loss, net of tax	0	0
Total other comprehensive income	(121,113)	80,177
Ending balance, June 30	(387,360)	(323,764)
Total [Member]
AOCI Attributable to Parent [Roll Forward]
Beginning balance, January 1	(852,592)	(1,013,021)
Ending balance, June 30	$ (943,351)	$ (921,389)