Savings Plans, Pension Plans and Other Postretirement Employee Benefits (Schedule of Estimated Future Benefit Payments) (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Pension Plans [Member]
2018	$ 28,536
2019	28,264
2020	27,951
2021	27,588
2022	27,255
2022–2026	128,115
OPEB [Member]
2018	3,704
2019	3,454
2020	3,231
2021	2,944
2022	2,760
2022–2026	$ 10,557

Amount of benefits for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following latest fiscal year.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Amount of benefits for defined benefit plan expected to be paid in next fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in fifth fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in fourth fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in third fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in second fiscal year following latest fiscal year.

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