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

Fair value of all liability derivatives designated as cash flow hedging instruments.

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

Name:	us-gaap_CashFlowHedgeDerivativeInstrumentLiabilitiesAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant