Retirement Benefit Plans (Assumed Health Care Cost Trend Rates) (Details) - Other Post-Retirement Benefits [Member] $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Aggregated service and interest cost, 1% Decrease in Rates	$ 722
Postretirement benefit obligation, 1% Decrease in Rates	20,964
Aggregated service and interest cost, Assumed Rates	797
Postretirement benefit obligation, Assumed Rates	23,036
Aggregated service and interest cost, 1% Increase in Rates	889
Postretirement benefit obligation, 1% Increase in Rates	$ 25,564

Defined benefit plan assumed rates accumulated postretirement benefit obligation.

No definition available.

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- Definition

Defined benefit plan assumed rates service and interest cost components.

+ References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (m)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

+ Details

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- Definition

Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

+ References

+ Details

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- Definition

The effect of a one-percentage-point increase in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

+ References

+ Details

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- Definition

The effect of a one-percentage-point increase in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

+ References

+ Details

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