Other Comprehensive Income (Loss) - Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net (gain) loss	$ 630	$ (704)			$ 16,957	$ 7,321
Reclassification adjustments	9,498	10,642			31,479	33,958
Total before tax	151,057	121,275			426,552	340,469
Provision for income taxes	35,343	17,427			95,987	63,759
Net income	(115,742)	(103,848)	$ (70,864)	$ (101,998)	(330,645)	(276,710)
Reclassification out of Accumulated Other Comprehensive Income | Net Prior Service Attributable to Parent
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net (gain) loss	1,175	462			14,238	2,767
Reclassification out of Accumulated Other Comprehensive Income | Retirement Benefits Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	1,175	462			14,238	2,767
Provision for income taxes	(335)	(171)			(3,443)	(811)
Net income	840	291			10,795	1,956
Reclassification out of Accumulated Other Comprehensive Income | Cumulative Unrealized Gain (Loss) on Derivatives
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification adjustments	0	869			3,275	5,153
Total before tax	0	869			3,275	5,153
Provision for income taxes	0	(197)			(744)	(1,171)
Net income	$ 0	$ 672			$ 2,531	$ 3,982