Other Comprehensive Income (Loss) - Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net (gain) loss	$ (704)			$ 1,219			$ 7,321	$ 701
Reclassification adjustments	10,642			11,330			33,958	33,262
Income before income taxes	(121,275)			(129,216)			(340,469)	(410,867)
Provision for income taxes	17,427			24,022			63,759	82,196
Net income	(103,848)	$ (70,864)	$ (101,998)	(105,194)	$ (113,209)	$ (110,268)	(276,710)	(328,671)
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	462			2,188			2,767	5,579
Reclassification out of Accumulated Other Comprehensive Income | Retirement Benefits Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	462			2,188			2,767	5,579
Provision for income taxes	(171)			(525)			(811)	(1,398)
Net income	291			1,663			1,956	4,181
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	869			1,566			5,153	4,737
Income before income taxes	869			1,566			5,153	4,737
Provision for income taxes	(197)			(356)			(1,171)	(1,076)
Net income	$ 672			$ 1,210			$ 3,982	$ 3,661