Accumulated Other Comprehensive Loss - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of year	$ 5,804,611	$ 5,197,642
Before reclassifications to income		19,336
Reclassifications to income	14,402	16,290
Other comprehensive income (loss)	(27,172)	35,626	$ (147,544)
Balance at end of year	4,394,147	5,804,611	5,197,642
Reclassifications before taxes, included in net periodic benefit expense	1,525	6,335
Reclassifications, income tax expense	321	1,330
Foreign Currency Translation Gains (Losses)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of year	(353,252)	(419,852)
Before reclassifications to income	29,241	66,600
Reclassifications to income	0	0
Other comprehensive income (loss)	29,241	66,600
Balance at end of year	(324,011)	(353,252)	(419,852)
Retirement and Postretirement Benefit Plan Adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of year	(218,015)	(182,036)
Before reclassifications to income	(70,815)	(47,264)
Reclassifications to income	13,198	11,285
Other comprehensive income (loss)	(57,617)	(35,979)
Balance at end of year	(275,632)	(218,015)	(182,036)
Reclassifications before taxes, included in net periodic benefit expense	17,694	14,380
Deferred Loss on Interest Rate Derivative Hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of year	(2,894)	(7,899)
Before reclassifications to income	0	0
Reclassifications to income	1,204	5,005
Other comprehensive income (loss)	1,204	5,005
Balance at end of year	(1,690)	(2,894)	(7,899)
Reclassifications, income tax expense	4,496	3,095
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of year	(574,161)	(609,787)
Before reclassifications to income	(41,574)
Balance at end of year	$ (601,333)	$ (574,161)	$ (609,787)