Other Comprehensive Income (Loss) - Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net (gain) loss	$ 1,219			$ 934			$ 701	$ (3,565)
Reclassification adjustments	11,330			10,958			33,262	33,098
Income before income taxes	(129,216)			(133,241)			(410,867)	(400,114)
Provision for income taxes	24,022			26,889			82,196	87,678
Net income	(105,194)	$ (113,209)	$ (110,268)	(106,352)	$ (107,126)	$ (98,958)	(328,671)	(312,436)
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	2,188			1,725			5,579	5,396
Reclassification out of Accumulated Other Comprehensive Income | Retirement Benefits Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	2,188			1,725			5,579	5,396
Provision for income taxes	(525)			(455)			(1,398)	(1,417)
Net income	1,663			1,270			4,181	3,979
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	1,566			1,610			4,737	4,869
Income before income taxes	1,566			1,610			4,737	4,869
Provision for income taxes	(356)			(366)			(1,076)	(1,105)
Net income	$ 1,210			$ 1,244			$ 3,661	$ 3,764