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Schedule of Minimum and Maximum Market Value of Plan Assets (Detail) | Dec. 31, 2017
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Equity Securities | Minimum |
Schedule of Pension and Other Postretirement Plan Assets by Fair Value [Line Items] |
Market value objective for plan assets | 55.00%
Equity Securities | Maximum |
Schedule of Pension and Other Postretirement Plan Assets by Fair Value [Line Items] |
Market value objective for plan assets | 75.00%
Debt Securities | Minimum |
Schedule of Pension and Other Postretirement Plan Assets by Fair Value [Line Items] |
Market value objective for plan assets | 25.00%
Debt Securities | Maximum |
Schedule of Pension and Other Postretirement Plan Assets by Fair Value [Line Items] |
Market value objective for plan assets | 45.00%
Investment Grade Bonds | Minimum |
Schedule of Pension and Other Postretirement Plan Assets by Fair Value [Line Items] |
Market value objective for plan assets | 0.00%
Investment Grade Bonds | Maximum |
Schedule of Pension and Other Postretirement Plan Assets by Fair Value [Line Items] |
Market value objective for plan assets | 20.00%
Cash and Cash Equivalents | Minimum |
Schedule of Pension and Other Postretirement Plan Assets by Fair Value [Line Items] |
Market value objective for plan assets | 0.00%
Cash and Cash Equivalents | Maximum |
Schedule of Pension and Other Postretirement Plan Assets by Fair Value [Line Items] |
Market value objective for plan assets | 10.00%

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- Definition Schedule of Pension and Other Postretirement Plan Assets by Fair Value [Line Items] + References No definition available. + Details
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- Definition Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one 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 (d)(5)(i) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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