Other Comprehensive Income (Loss) - Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net (gain) loss	$ 6,460		$ (378)		$ 8,025	$ (518)
Reclassification adjustments	12,439		11,011		23,316	21,932
Income before income taxes	(91,695)		(144,650)		(219,194)	(281,651)
Provision for income taxes	20,831		31,441		46,332	58,174
Net income	(70,864)	$ (101,998)	(113,209)	$ (110,268)	(172,862)	(223,477)
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	(569)		1,691		2,305	3,391
Reclassification out of Accumulated Other Comprehensive Income | Retirement Benefits Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	(569)		1,691		2,305	3,391
Provision for income taxes	(62)		(435)		(640)	(873)
Net income	(631)		1,256		1,665	2,518
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	2,739		1,583		4,284	3,171
Income before income taxes	2,739		1,583		4,284	3,171
Provision for income taxes	(623)		(359)		(974)	(720)
Net income	$ 2,116		$ 1,224		$ 3,310	$ 2,451