Earnings Per Common Share - Basic Earnings Per Common Share (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, Basic, by Common Class, Including Two Class Method [Line Items]
Total (in usd per share)	[1]	$ 0.07	$ 0.10	$ 0.16	$ 0.20
Basic weighted average common shares outstanding (in shares)		32,628	31,955	32,485	31,611
Class A Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings (in usd per share)		$ 0.11	$ 0.11	$ 0.33	$ 0.33
Undistributed losses (in usd per share)		(0.04)	(0.01)	(0.17)	(0.13)
Total (in usd per share)		$ 0.07	$ 0.10	$ 0.16	$ 0.20
Distributed earnings		$ 3,396	$ 3,321	$ 10,142	$ 9,873
Undistributed losses		(1,214)	(223)	(5,387)	(4,033)
Total		$ 2,182	$ 3,098	$ 4,755	$ 5,840
Basic weighted average common shares outstanding (in shares)		30,806	30,133	30,663	29,789
Class B Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings (in usd per share)		$ 0.11	$ 0.11	$ 0.33	$ 0.33
Undistributed losses (in usd per share)		(0.04)	(0.01)	(0.17)	(0.13)
Total (in usd per share)		$ 0.07	$ 0.10	$ 0.16	$ 0.20
Distributed earnings		$ 201	$ 201	$ 602	$ 604
Undistributed losses		(72)	(13)	(320)	(247)
Total		$ 129	$ 188	$ 282	$ 357
Basic weighted average common shares outstanding (in shares)		1,822	1,822	1,822	1,822

[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.