Earnings Per Common Share - Diluted Earnings per Share for Class B Common Shares Using Two-Class Method (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
		Jul. 31, 2021	Jul. 31, 2020
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Basic weighted aveage common shares outstanding (in shares)		33,053,000	32,339,000
Diluted EPS for class B common shares (in shares)		33,946,000	32,932,000
Basic EPS (in usd per share)	[1]	$ 0.09	$ 0.06
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & distributed earnings		$ 163	$ 114
Reallocation of undistributed earnings/losses from Class A Common Shares to Class B Common Shares		1	2
Net earnings		$ 164	$ 116
Basic weighted aveage common shares outstanding (in shares)		1,822,000	1,822,000
Diluted EPS for class B common shares (in shares)		1,822,000	1,822,000
Basic EPS (in usd per share)		$ 0.09	$ 0.06
Diluted EPS (in usd per share)		$ 0.09	$ 0.06

[1] Basic per share amounts are the same for Class A and Class B shares. Diluted per share amounts for Class A shares are shown above. Diluted earnings per share for Class B shares under the two-class method are $0.09 and $0.06 for the three months ended July 31, 2021 and 2020. See Note D to the Condensed Consolidated Financial Statements.