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Pension and Employee Benefit Plans - Details of Defined Benefit Pension Plan Asset Allocation by Asset Category (Detail) | Dec. 31, 2017 | Dec. 31, 2016
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Defined Benefit Plan Disclosure [Line Items] |  |
Target Allocation | 100.00% |
Percentage of Plan Assets | 100.00% | 100.00%
Cash and cash equivalents [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target Allocation | 0.00% |
Percentage of Plan Assets | 4.00% | 4.00%
Equity Securities [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target Allocation | 70.00% |
Percentage of Plan Assets | 70.00% | 67.00%
Debt Securities [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target Allocation | 30.00% |
Percentage of Plan Assets | 26.00% | 29.00%

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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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- Definition Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2446-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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