Other Comprehensive Income (Loss) - Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of service cost	$ (140)	$ (4,449)
Reclassification adjustments	10,921	11,000
Income before income taxes	(137,001)	(130,132)
Provision for income taxes	26,733	31,174
Net income	(110,268)	(98,958)
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	1,700	1,918
Reclassification out of Accumulated Other Comprehensive Income | Retirement Benefits Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	1,700	1,918
Provision for income taxes	(438)	(505)
Net income	1,262	1,413
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	1,588	1,632
Income before income taxes	1,588	1,632
Provision for income taxes	(361)	(371)
Net income	$ 1,227	$ 1,261