Business, Basis of Presentation and Summary of Significant Accounting Policies - Advertising Expense and Credit and Economic Risk (Details) $ in Millions	12 Months Ended
Apr. 30, 2020 USD ($) customer	Apr. 30, 2019 USD ($) customer	Apr. 30, 2018 USD ($)
Selling, general and administrative expenses
Advertising Expense
Advertising Expense \| $	$ 3.3	$ 1.9	$ 1.8
Accounts receivable
Advertising Expense
Number of major customers \| customer	0	0

Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 720
-SubTopic 35
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6420018&loc=d3e36677-107848

Name:	us-gaap_AdvertisingExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration