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, 2020	Jan. 31, 2019	Jan. 31, 2020	Jan. 31, 2019
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total (in usd per share)	[1]	$ 0.10	$ 0.07	$ 0.20	$ 0.16
Basic weighted aveage common shares outstanding (in shares)		31,955	31,010	31,611	30,887
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)		(0.01)	(0.04)	(0.13)	(0.17)
Total (in usd per share)		$ 0.10	$ 0.07	$ 0.20	$ 0.16
Distributed earnings		$ 3,321	$ 3,213	$ 9,873	$ 9,609
Undistributed losses		(223)	(1,047)	(4,033)	(4,974)
Total		$ 3,098	$ 2,166	$ 5,840	$ 4,635
Basic weighted aveage common shares outstanding (in shares)		30,133	29,188	29,789	29,036
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)		(0.01)	(0.04)	(0.13)	(0.17)
Total (in usd per share)		$ 0.10	$ 0.07	$ 0.20	$ 0.16
Distributed earnings		$ 201	$ 204	$ 604	$ 613
Undistributed losses		(13)	(69)	(247)	(319)
Total		$ 188	$ 135	$ 357	$ 294
Basic weighted aveage common shares outstanding (in shares)		1,822	1,822	1,822	1,851

[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.