Stock-Based Compensation, Director Stock Awards (Details) - Director Stock Plan [Member] - Class A Common Stock [Member] - Non-Employee Directors [Member] - shares	12 Months Ended
Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Value of annual award as percentage of annual director retainer fee based on stock price on date of grant	100.00%
Shares awarded under the plan (in shares)	28,360	20,048	18,991

Number of shares issued pursuant to the terms of a deferred compensation arrangement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (l)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

Name:	us-gaap_DeferredCompensationArrangementWithIndividualSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration