Other Comprehensive Income (Loss) - Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of service cost	$ (4,449)	$ (308)
Reclassification adjustments	11,000	11,552
Income before income taxes	130,132	104,427
Provision for income taxes	31,174	28,528
Net income	(98,958)	(75,899)
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Including Portion Attributable to Noncontrolling Interest
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of service cost	1,918	1,676
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment Including Portion Attributable to Noncontrolling Interest
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	(1,918)	(1,676)
Provision for income taxes	(505)	(552)
Net income	1,413	1,124
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification adjustments	1,632	1,677
Income before income taxes	(1,632)	(1,677)
Provision for income taxes	(371)	(635)
Net income	$ 1,261	$ 1,042