Financial Instruments - Fair Value of Derivative Designated as Cash Flow Hedge Instrument (Detail) - USD ($) $ in Thousands	Jan. 31, 2019	Apr. 30, 2018
Designated as Hedge Instrument \| Interest Rate Swap
Derivative asset:
Interest rate swap contract	$ 1,128	$ 2,076

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

Name:	us-gaap_CashFlowHedgeDerivativeInstrumentAssetsAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant