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Financial Instruments - Fair Value of Derivative Designated as Cash Flow Hedge Instrument (Detail) - USD ($) $ in Thousands | Oct. 31, 2017 | Apr. 30, 2017
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Designated as Hedge Instrument | Interest Rate Swap |  |
Derivative liability: |  |
Interest rate swap contract | $ 303 | $ 947

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- Definition Fair value of all liability derivatives designated as cash flow hedging instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4B -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624163-113959 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |