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
		Jul. 31, 2019	Jul. 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)		31,270	30,725
Diluted EPS for class B common shares (in shares)		31,951	31,343
Basic EPS (in usd per share)	[1]	$ 0.04	$ 0.05
Diluted EPS (in usd per share)	[1]	$ 0.04	$ 0.04
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & distributed earnings		$ 70	$ 86
Reallocation of undistributed earnings from Class A Common Shares to Class B Common Shares		3	2
Net earnings		$ 73	$ 88
Basic shares used in calculation of earnings per common share (in shares)		1,822	1,911
Diluted EPS for class B common shares (in shares)		1,822	1,911
Basic EPS (in usd per share)		$ 0.04	$ 0.05
Diluted EPS (in usd per share)		$ 0.04	$ 0.05

[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 $0.04 and $0.05 for the three months ended July 31, 2019 and 2018, respectively. See Note E to the Condensed Consolidated Financial Statements.