Earnings Per Common Share - Diluted Earnings per Share for Class B Common Shares Using Two-Class Method (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Basic weighted average common shares outstanding (in shares)		32,489	31,609	32,414	31,440
Diluted EPS for class B common shares (in shares)		32,896	32,310	32,919	32,066
Basic EPS (in usd per share)	[1]	$ 0.02	$ 0.06	$ 0.08	$ 0.09
Diluted EPS (in usd per share)	[1]	$ 0.02	$ 0.05	$ 0.08	$ 0.09
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & distributed earnings		$ 39	$ 101	$ 153	$ 169
Reallocation of undistributed earnings/losses from Class A Common Shares to Class B Common Shares		2	3	4	6
Net earnings		$ 41	$ 104	$ 157	$ 175
Basic weighted average common shares outstanding (in shares)		1,822	1,822	1,822	1,822
Diluted EPS for class B common shares (in shares)		1,822	1,822	1,822	1,822
Basic EPS (in usd per share)		$ 0.02	$ 0.06	$ 0.08	$ 0.09
Diluted EPS (in usd per share)		$ 0.02	$ 0.06	$ 0.09	$ 0.10

[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 $0.02 and $0.06 for the three months ended October 31, 2020 and 2019 and $0.09 and $0.10 for the six months ended October 31, 2020 and 2019. See Note E to the Condensed Consolidated Financial Statements.