Other Comprehensive Income (Loss) - Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net (gain) loss	$ 17,175	$ 6,460		$ 16,327	$ 8,025
Reclassification adjustments	11,205	12,439		21,981	23,316
Income before income taxes	(129,876)	(91,695)		(275,495)	(219,194)
Provision for income taxes	27,697	20,831		60,644	46,332
Net income	(102,195)	(70,864)	$ (101,998)	(214,903)	(172,862)
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	12,009	(569)		13,063	2,305
Reclassification out of Accumulated Other Comprehensive Income | Retirement Benefits Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	12,009	(569)		13,063	2,305
Provision for income taxes	(2,799)	(62)		(3,108)	(640)
Net income	9,210	(631)		9,955	1,665
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	2,416	2,739		3,275	4,284
Income before income taxes	2,416	2,739		3,275	4,284
Provision for income taxes	(549)	(623)		(744)	(974)
Net income	$ 1,867	$ 2,116		$ 2,531	$ 3,310