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Components of Net Periodic Benefits Costs (Parenthetical) (Detail) | 3 Months Ended
--- | ---
Jul. 31, 2017 | Jul. 31, 2016
Defined Benefit Plan Disclosure [Line Items] |  |
Expected long-term rate of return on plan assets | 6.50% | 6.50%

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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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Data Type: | num:percentItemType
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Period Type: | duration

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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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Namespace Prefix: | us-gaap_
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