Employee and Retiree Benefit Plans (Plans' Benefit Obligations and Fair Value of Assets and Statement of Funded Status) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Change in plan assets
Total beginning balance	$ 519,357
Total ending balance	563,825	$ 519,357
Pension Benefits [Member]
Change in benefit obligation
Obligation at January 1	881,932	815,593	$ 794,589	$ 881,932	$ 815,593
Service cost	8,279	8,136	17,948
Interest cost	27,047	25,185	33,168
Participant contributions
Actuarial loss (gain)	60,855	58,236
Medicare Part D subsidy
Exchange rate changes	18,751	(30,447)
Benefits paid	39,910	40,928
Curtailments		822
Other	(8,683)
Obligation at December 31	881,932	815,593	794,589
Change in plan assets
Total beginning balance	519,357	521,682
Actual return on plan assets	50,079	61,860
Employer contributions	24,918	8,186
Participant contributions
Medicare Part D subsidy
Exchange rate changes	18,064	(30,609)
Benefits paid	(39,910)	(40,928)
Other				(8,683)	(834)
Total ending balance	563,825	519,357	521,682
Funded status and amounts recognized in the Consolidated Balance Sheets at December 31
Deferred charges and other assets				5,905	7,591
Other accrued liabilities				(8,856)	(8,184)
Deferred credits and other liabilities				(315,156)	(295,643)
Funded status and net plan liability recognized at December 31				(318,107)	(296,236)
Other Postretirement Benefits [Member]
Change in benefit obligation
Obligation at January 1	106,276	106,679	115,222	106,276	106,679
Service cost	1,601	1,864	3,180
Interest cost	3,444	3,800	4,883
Participant contributions	2,075	1,278
Actuarial loss (gain)	(3,077)	(10,627)
Medicare Part D subsidy	318	510
Exchange rate changes	46	20
Benefits paid	4,810	5,369
Curtailments		(19)
Other
Obligation at December 31	106,276	106,679	115,222
Change in plan assets
Total beginning balance
Actual return on plan assets
Employer contributions	2,417	3,581
Participant contributions	2,075	1,278
Medicare Part D subsidy	318	510
Exchange rate changes
Benefits paid	(4,810)	(5,369)
Other
Total ending balance
Funded status and amounts recognized in the Consolidated Balance Sheets at December 31
Deferred charges and other assets
Other accrued liabilities				(5,392)	(5,267)
Deferred credits and other liabilities				(100,884)	(101,412)
Funded status and net plan liability recognized at December 31				$ (106,276)	$ (106,679)