Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive (Loss) by Component (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
AOCI Attributable to Parent [Roll Forward]
Beginning balance	$ 3,204,796
Other comprehensive income (loss) before reclassifications	6,836	$ (103,416)
Amounts reclassified from accumulated other comprehensive loss	26,112	32,352
Other comprehensive income (loss), net of income taxes	32,948	(71,064)
Ending balance	3,233,879
Pension and Other Post-Retirement Benefits
AOCI Attributable to Parent [Roll Forward]
Beginning balance	(692,868)	(704,415)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	18,630	16,292
Other comprehensive income (loss), net of income taxes	18,630	16,292
Ending balance	(674,238)	(688,123)
Cash Flow Hedges
AOCI Attributable to Parent [Roll Forward]
Beginning balance	(30,007)	(20,671)
Other comprehensive income (loss) before reclassifications	0	(21,046)
Amounts reclassified from accumulated other comprehensive loss	7,482	4,704
Other comprehensive income (loss), net of income taxes	7,482	(16,342)
Ending balance	(22,525)	(37,013)
Foreign Currency Translation
AOCI Attributable to Parent [Roll Forward]
Beginning balance	(313,627)	(416,222)
Other comprehensive income (loss) before reclassifications	6,836	(82,370)
Amounts reclassified from accumulated other comprehensive loss	0	11,356
Other comprehensive income (loss), net of income taxes	6,836	(71,014)
Ending balance	(306,791)	(487,236)
Total
AOCI Attributable to Parent [Roll Forward]
Beginning balance	(1,036,502)	(1,141,308)
Ending balance	$ (1,003,554)	$ (1,212,372)