Employee Benefits Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Amortization of:
Postretirement benefit income	$ 56,833	$ 61,215	$ 41,704
Company-administered plans:
Pension expense from continuing operations
Service cost	12,345	12,977	13,820
Interest cost	86,431	94,476	88,013
Expected return on plan assets	(91,062)	(90,588)	(98,892)
Amortization of:
Net actuarial gain	32,987	31,777	30,741
Prior service cost (credit)	579	2,976	(306)
Postretirement benefit income	41,280	51,618	33,376
Union-administered plans
Amortization of:
Postretirement benefit income	15,553	9,597	8,328
United States | Company-administered plans:
Amortization of:
Postretirement benefit income	43,717	53,319	34,986
Domestic Plan | Company-administered plans:
Amortization of:
Postretirement benefit income	$ (2,437)	$ (1,701)	$ (1,610)