Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	$ 1,803,999	$ 1,773,949	$ 1,844,277
Other comprehensive income, before reclassifications	146,462	105,777	(77,251)
Income tax expense	(28,005)	(23,124)	14,640
Total other comprehensive income before reclassifications, net of tax	118,457	82,653	(62,611)
Reclassifications	(82,555)	13,288	53,976
Income tax benefit (expense)	17,630	(3,206)	(12,652)
Total reclassification from other comprehensive income, net of tax	(64,925)	10,082	41,324
Total other comprehensive loss, net of tax	53,532	92,735	(21,287)
Balance, end of period	1,722,785	1,803,999	1,773,949
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(536,949)	(629,684)	(500,049)
Total other comprehensive loss, net of tax	53,532	92,735	(21,287)
Reclassification of certain tax effects			(108,348)
Balance, end of period	(483,417)	(536,949)	(629,684)
Foreign currency translation adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(40,813)	(49,608)	(21,852)
Other comprehensive income, before reclassifications	37,088	9,229	(28,212)
Income tax expense	(3,864)	(434)	3,202
Total other comprehensive income before reclassifications, net of tax	33,224	8,795	(25,010)
Reclassifications	0	0	0
Income tax benefit (expense)	0	0	0
Total reclassification from other comprehensive income, net of tax	0	0	0
Total other comprehensive loss, net of tax	33,224	8,795	(25,010)
Reclassification of certain tax effects			(2,746)
Balance, end of period	(7,589)	(40,813)	(49,608)
Derivative financial instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(14,586)	1,785	(17,254)
Other comprehensive income, before reclassifications	107,181	6,477	35,686
Income tax expense	(23,626)	(1,541)	(8,455)
Total other comprehensive income before reclassifications, net of tax	83,555	4,936	27,231
Reclassifications	(148,107)	(27,732)	(9,466)
Income tax benefit (expense)	33,022	6,425	2,244
Total reclassification from other comprehensive income, net of tax	(115,085)	(21,307)	(7,222)
Total other comprehensive loss, net of tax	(31,530)	(16,371)	20,009
Reclassification of certain tax effects			(970)
Balance, end of period	(46,116)	(14,586)	1,785
Derivative financial instruments | Net (gain) loss on Derivative Instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassifications	148,107	27,732	9,466
Pension and postretirement benefit plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(481,550)	(581,861)	(460,943)
Other comprehensive income, before reclassifications	2,193	90,071	(84,725)
Income tax expense	(515)	(21,149)	19,893
Total other comprehensive income before reclassifications, net of tax	1,678	68,922	(64,832)
Reclassifications	65,552	41,020	63,442
Income tax benefit (expense)	(15,392)	(9,631)	(14,896)
Total reclassification from other comprehensive income, net of tax	50,160	31,389	48,546
Total other comprehensive loss, net of tax	51,838	100,311	(16,286)
Reclassification of certain tax effects			(104,632)
Balance, end of period	(429,712)	(481,550)	(581,861)
Pension and postretirement benefit plans; Prior service credits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassifications	(3,469)	(4,311)	(2,262)
Pension and postretirement benefit plans; Actuarial losses
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassifications	65,981	44,788	66,590
Pension and postretirement benefit plans; Curtailment and settlement losses
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassifications	$ 3,040	$ 543	$ (886)