Earnings Per Common Share - Basic Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total (in usd per share)	[1]	$ 0.06	$ 0.04	$ 0.09	$ 0.09
Basic (in shares)		31,609	30,926	31,440	30,825
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	$ 0.22	$ 0.22
Undistributed losses (in usd per share)		(0.05)	(0.07)	(0.13)	(0.13)
Total (in usd per share)		$ 0.06	$ 0.04	$ 0.09	$ 0.09
Distributed earnings		$ 3,303	$ 3,200	$ 6,552	$ 6,396
Undistributed losses		(1,645)	(2,033)	(3,810)	(3,927)
Total		$ 1,658	$ 1,167	$ 2,742	$ 2,469
Basic (in shares)		29,787	29,104	29,618	28,959
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	$ 0.22	$ 0.22
Undistributed losses (in usd per share)		(0.05)	(0.07)	(0.13)	(0.13)
Total (in usd per share)		$ 0.06	$ 0.04	$ 0.09	$ 0.09
Distributed earnings		$ 202	$ 205	$ 403	$ 409
Undistributed losses		(101)	(129)	(234)	(250)
Total		$ 101	$ 76	$ 169	$ 159
Basic (in shares)		1,822	1,822	1,822	1,866

[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 $0.06 and $0.04 for the three months ended October 31, 2019 and 2018, and $0.10 and $0.09 for the six months ended October 31, 2019 and 2018 respectively. See Note E to the Condensed Consolidated Financial Statements.