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Retirement Benefit Plans (Schedule of Assumptions Used) (Details) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Supplemental Employee Retirement Plans, Defined Benefit |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Discount rate (percentage) | 3.45% | 3.85%
Composite rate of compensation increase (percentage) | 3.00% | 3.00%
Net periodic pension expense, discount rate (percentage) | 3.85% | 4.05%
Net periodic pension expense, rate of compensation increase (percentage) | 3.00% | 3.00%
Hourly Employees’ Pension Plan | Pension Plans, Defined Benefit |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net periodic pension expense, discount rate (percentage) |  | 4.30%
Net periodic pension expense, Long-term rate of return on plan assets (percentage) |  | 7.25%
Employees’ Retirement Plan | Pension Plans, Defined Benefit |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Discount rate (percentage) | 3.60% | 4.10%
Net periodic pension expense, discount rate (percentage) | 4.10% | 4.40%
Net periodic pension expense, Long-term rate of return on plan assets (percentage) | 7.25% | 7.25%

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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan. + 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 (k)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan. + 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 (k)(2) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan. + 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 (k)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + 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 (k)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan. + 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 (k)(2) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + 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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