Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	$ 1,773,949	$ 1,844,277	$ 1,920,158
Other comprehensive income, before reclassifications	105,777	(77,251)	23,433
Income tax expense	(23,124)	14,640	8,060
Net other comprehensive (loss) income before reclassifications	82,653	(62,611)	31,493
Reclassifications	13,288	53,976	53,745
Income tax benefit (expense)	(3,206)	(12,652)	(19,906)
Net reclassifications	10,082	41,324	33,839
Total other comprehensive (loss) income, net of tax	92,735	(21,287)	65,332
Reclassification of certain tax effects		(108,348)
Balance, end of period	1,803,999	1,773,949	1,844,277
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(629,684)	(500,049)	(565,381)
Total other comprehensive (loss) income, net of tax	92,735	(21,287)	65,332
Balance, end of period	(536,949)	(629,684)	(500,049)
Foreign currency translation adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(49,608)	(21,852)	(68,132)
Other comprehensive income, before reclassifications	9,229	(28,212)	52,145
Income tax expense	(434)	3,202	(5,865)
Net other comprehensive (loss) income before reclassifications	8,795	(25,010)	46,280
Reclassifications	0	0	0
Income tax benefit (expense)	0	0	0
Net reclassifications	0	0	0
Total other comprehensive (loss) income, net of tax	8,795	(25,010)	46,280
Reclassification of certain tax effects		(2,746)
Balance, end of period	(40,813)	(49,608)	(21,852)
Marketable securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	0	0	(1,194)
Other comprehensive income, before reclassifications	0	0	1,896
Income tax expense	0	0	(702)
Net other comprehensive (loss) income before reclassifications	0	0	1,194
Reclassifications	0	0	0
Income tax benefit (expense)	0	0	0
Net reclassifications	0	0	0
Total other comprehensive (loss) income, net of tax	0	0	1,194
Reclassification of certain tax effects		0
Balance, end of period	0	0	0
Derivative financial instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	1,785	(17,254)	12,524
Other comprehensive income, before reclassifications	6,477	35,686	(54,929)
Income tax expense	(1,541)	(8,455)	20,338
Net other comprehensive (loss) income before reclassifications	4,936	27,231	(34,591)
Reclassifications	(27,732)	(9,466)	7,644
Income tax benefit (expense)	6,425	2,244	(2,831)
Net reclassifications	(21,307)	(7,222)	4,813
Total other comprehensive (loss) income, net of tax	(16,371)	20,009	(29,778)
Reclassification of certain tax effects		(970)
Balance, end of period	(14,586)	1,785	(17,254)
Derivative financial instruments | Net (gain) loss on Derivative Instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassifications	27,732	9,466	(7,644)
Pension and postretirement benefit plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(581,861)	(460,943)	(508,579)
Other comprehensive income, before reclassifications	90,071	(84,725)	24,321
Income tax expense	(21,149)	19,893	(5,711)
Net other comprehensive (loss) income before reclassifications	68,922	(64,832)	18,610
Reclassifications	41,020	63,442	46,101
Income tax benefit (expense)	(9,631)	(14,896)	(17,075)
Net reclassifications	31,389	48,546	29,026
Total other comprehensive (loss) income, net of tax	100,311	(16,286)	47,636
Reclassification of certain tax effects		(104,632)
Balance, end of period	(481,550)	(581,861)	(460,943)
Pension and postretirement benefit plans; Prior service credits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassifications	(4,311)	(2,262)	(1,153)
Pension and postretirement benefit plans; Actuarial losses
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassifications	44,788	66,590	$ 47,254
Pension and postretirement benefit plans; Curtailment and settlement losses
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassifications	$ 543	$ (886)