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		9 Months Ended
		Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2020	Jan. 31, 2019
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Basic weighted aveage common shares outstanding (in shares)		31,955	31,010	31,611	30,887
Diluted EPS for class B common shares (in shares)		32,668	31,183	32,260	31,351
Basic EPS (in usd per share)	[1]	$ 0.10	$ 0.07	$ 0.20	$ 0.16
Diluted EPS (in usd per share)	[1]	$ 0.10	$ 0.07	$ 0.19	$ 0.16
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & distributed earnings		$ 188	$ 135	$ 357	$ 294
Reallocation of undistributed earnings/losses from Class A Common Shares to Class B Common Shares		0	1	5	1
Net earnings		$ 188	$ 136	$ 362	$ 295
Basic weighted aveage common shares outstanding (in shares)		1,822	1,822	1,822	1,851
Diluted EPS for class B common shares (in shares)		1,822	1,822	1,822	1,851
Basic EPS (in usd per share)		$ 0.10	$ 0.07	$ 0.20	$ 0.16
Diluted EPS (in usd per share)		$ 0.10	$ 0.07	$ 0.20	$ 0.16

[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 $0.10 and $0.07 for the three months ended January 31, 2020 and 2019, and $0.20 and $0.16 for the nine months ended January 31, 2020 and 2019 respectively. See Note E to the Condensed Consolidated Financial Statements.