Earnings Per Common Share - Basic Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended
		Jul. 31, 2019	Jul. 31, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total (in usd per share)	[1]	$ 0.04	$ 0.05
Basic weighted average common shares outstanding (in shares)		31,270	30,725
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
Undistributed losses (in usd per share)		(0.07)	(0.06)
Total (in usd per share)		$ 0.04	$ 0.05
Distributed earnings (in usd)		$ 3,245	$ 3,189
Undistributed losses (in usd)		(2,163)	(1,890)
Total (in usd)		$ 1,082	$ 1,299
Basic weighted average common shares outstanding (in shares)		29,448	28,814
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
Undistributed losses (in usd per share)		(0.07)	(0.06)
Total (in usd per share)		$ 0.04	$ 0.05
Distributed earnings (in usd)		$ 206	$ 211
Undistributed losses (in usd)		(136)	(125)
Total (in usd)		$ 70	$ 86
Basic weighted average common shares outstanding (in shares)		1,822	1,911

[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 $0.04 and $0.05 for the three months ended July 31, 2019 and 2018, respectively. See Note E to the Condensed Consolidated Financial Statements.