Accounting Policies Revenue recognition policy (Details)	12 Months Ended
Apr. 30, 2020	Apr. 30, 2019
Revenue recognition policy [Abstract]
Revenue, Transaction Price Measurement, Tax Exclusion [true false]	true	true

Indicates (true false) whether accounting policy was elected to exclude from measurement of transaction price tax assessed by governmental authority that was both imposed on and concurrent with specific revenue-producing transaction, and collected from customer. Includes, but is not limited to, sales, use, value-added, and excise tax.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 32
-Paragraph 2A
-URI http://asc.fasb.org/extlink&oid=116855152&loc=SL82860478-203043

Name:	us-gaap_RevenueTransactionPriceMeasurementTaxExclusion
Namespace Prefix:	us-gaap_
Data Type:	xbrli:booleanItemType
Balance Type:	na
Period Type:	duration