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, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Basic shares used in calculation of earnings per common share (in shares)		31,609	30,926	31,440	30,825
Diluted EPS for class B common shares (in shares)		32,310	31,477	32,066	31,412
Basic EPS (in usd per share)	[1]	$ 0.06	$ 0.04	$ 0.09	$ 0.09
Diluted EPS (in usd per share)	[1]	$ 0.05	$ 0.04	$ 0.09	$ 0.08
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & distributed earnings		$ 101	$ 76	$ 169	$ 159
Reallocation of undistributed earnings from Class A Common Shares to Class B Common Shares		3	2	6	0
Net earnings		$ 104	$ 78	$ 175	$ 159
Basic shares used in calculation of earnings per common share (in shares)		1,822	1,822	1,822	1,866
Diluted EPS for class B common shares (in shares)		1,822	1,822	1,822	1,866
Basic EPS (in usd per share)		$ 0.06	$ 0.04	$ 0.09	$ 0.09
Diluted EPS (in usd per share)		$ 0.06	$ 0.04	$ 0.10	$ 0.09

[1] (a)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 $0.06 and $0.04 for the three months ended October 31, 2019 and 2018, and $0.10 and $0.09 for the six months ended October 31, 2019 and 2018 respectively. See Note E to the Condensed Consolidated Financial Statements.