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		6 Months Ended
		Oct. 31, 2021	Oct. 31, 2020	Oct. 31, 2021	Oct. 31, 2020
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Basic weighted aveage common shares outstanding (in shares)		33,337,000	32,489,000	33,195,000	32,414,000
Diluted EPS for class B common shares (in shares)		34,685,000	32,896,000	34,448,000	32,919,000
Basic EPS (in usd per share)	[1]	$ 0.10	$ 0.02	$ 0.19	$ 0.08
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & distributed earnings		$ 181	$ 39	$ 342	$ 153
Reallocation of undistributed earnings/losses from Class A Common Shares to Class B Common Shares		1	2	2	4
Net earnings		$ 182	$ 41	$ 344	$ 157
Basic weighted aveage common shares outstanding (in shares)		1,822,000	1,822,000	1,822,000	1,822,000
Diluted EPS for class B common shares (in shares)		1,822,000	1,822,000	1,822,000	1,822,000
Basic EPS (in usd per share)		$ 0.10	$ 0.02	$ 0.19	$ 0.08
Diluted EPS (in usd per share)		$ 0.10	$ 0.02	$ 0.19	$ 0.09

[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 $0.10 and $0.02 for the three months ended October 31, 2021 and 2020 and $0.19 and $0.09 for the six months ended October 31, 2021 and 2020. See Note D to the Condensed Consolidated Financial Statements.