Other Comprehensive Income (Loss) - Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of service cost	$ (378)		$ (50)		$ (518)	$ (4,499)
Reclassification adjustments	11,011		11,140		21,932	22,140
Income before income taxes	(144,650)		(136,741)		(281,651)	(266,873)
Provision for income taxes	31,441		29,615		58,174	60,789
Net income	(113,209)	$ (110,268)	(107,126)	$ (98,958)	(223,477)	(206,084)
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 service cost	1,691		1,753		3,391	3,671
Reclassification out of Accumulated Other Comprehensive Income | Retirement Benefits Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	1,691		1,753		3,391	3,671
Provision for income taxes	(435)		(457)		(873)	(962)
Net income	1,256		1,296		2,518	2,709
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	1,583		1,627		3,171	3,259
Income before income taxes	1,583		1,627		3,171	3,259
Provision for income taxes	(359)		(368)		(720)	(739)
Net income	$ 1,224		$ 1,259		$ 2,451	$ 2,520