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, 2021	Jan. 31, 2020	Jan. 31, 2021	Jan. 31, 2020
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Basic weighted average common shares outstanding (in shares)		32,628	31,955	32,485	31,611
Diluted EPS for class B common shares (in shares)		33,293	32,668	33,107	32,260
Basic EPS (in usd per share)	[1]	$ 0.07	$ 0.10	$ 0.16	$ 0.20
Diluted EPS (in usd per share)	[1]	$ 0.07	$ 0.10	$ 0.15	$ 0.19
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & distributed earnings		$ 129	$ 188	$ 282	$ 357
Reallocation of undistributed earnings/losses from Class A Common Shares to Class B Common Shares		2	0	6	5
Net earnings		$ 131	$ 188	$ 288	$ 362
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)		$ 0.07	$ 0.10	$ 0.16	$ 0.20
Diluted EPS (in usd per share)		$ 0.07	$ 0.10	$ 0.16	$ 0.20

[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 $0.07 and $0.10 for the three months ended January 31, 2021 and 2020, respectively, and $0.16 and $0.20 for the nine months ended January 31, 2021 and 2020, respectively. See Note E to the Condensed Consolidated Financial Statements.