Employee and Retiree Benefit Plans (Projected Benefit Obligations, Accumulated Benefit Obligations and Fair Value of Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Funded Plan [Member] \| Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected Benefit Obligations	$ 691,923	$ 643,174
Accumulated Benefit Obligations	640,230	599,730
Fair Value of Plan Assets	540,161	497,894
Unfunded Plan [Member] \| Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected Benefit Obligations	106,276	106,678
Accumulated Benefit Obligations	106,276	106,678
Unfunded Plan [Member] \| Nonqualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected Benefit Obligations	172,364	156,088
Accumulated Benefit Obligations	$ 163,319	$ 150,780

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- Definition

Amount of accumulated benefit obligation for defined benefit pension plan with accumulated benefit obligation in excess of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2417-114920

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- Definition

Fair value of plan assets for defined benefit pension plan with accumulated benefit obligation in excess of plan assets.

+ References

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- Definition

Amount of projected benefit obligation for defined benefit pension plan with accumulated benefit obligation in excess of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=77993564&loc=d3e4179-114921

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