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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] |
Cash and cash equivalents | 55.00%
Equity Securities | Maximum |
Schedule Of Pension And Other Postretirement Plan Assets By Fair Value [Line Items] |
Cash and cash equivalents | 75.00%
Debt Securities | Minimum |
Schedule Of Pension And Other Postretirement Plan Assets By Fair Value [Line Items] |
Cash and cash equivalents | 25.00%
Debt Securities | Maximum |
Schedule Of Pension And Other Postretirement Plan Assets By Fair Value [Line Items] |
Cash and cash equivalents | 45.00%
Investment Grade Bonds | Minimum |
Schedule Of Pension And Other Postretirement Plan Assets By Fair Value [Line Items] |
Cash and cash equivalents | 0.00%
Investment Grade Bonds | Maximum |
Schedule Of Pension And Other Postretirement Plan Assets By Fair Value [Line Items] |
Cash and cash equivalents | 20.00%
Cash and Cash Equivalents | Minimum |
Schedule Of Pension And Other Postretirement Plan Assets By Fair Value [Line Items] |
Cash and cash equivalents | 0.00%
Cash and Cash Equivalents | Maximum |
Schedule Of Pension And Other Postretirement Plan Assets By Fair Value [Line Items] |
Cash and cash equivalents | 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/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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