Earnings Per Common share - Basic Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended
		Jul. 31, 2018	Jul. 31, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total	[1]	$ 0.05	$ 0.09
Basic weighted average common shares outstanding		30,725	29,671
Class A Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings		$ 0.11	$ 0.11
Undistributed earnings		(0.06)	(0.02)
Total	[2]	$ 0.05	$ 0.09
Distributed earnings		$ 3,189	$ 3,014
Undistributed earnings		(1,890)	(502)
Total		$ 1,299	$ 2,512
Basic weighted average common shares outstanding		28,814	27,307
Class B Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings		$ 0.11	$ 0.11
Undistributed earnings		(0.06)	(0.02)
Total	[2]	$ 0.05	$ 0.09
Distributed earnings		$ 211	$ 256
Undistributed earnings		(125)	(43)
Total		$ 86	$ 213
Basic weighted average common shares outstanding		1,911	2,364

[1] Basic per share amounts are the same for Class A and Class B Common Shares. Diluted per share amounts for Class A Common Shares are shown above. Diluted earnings per share for Class B Common Shares under the two-class method are $0.04 and $0.09 for the three months ended July 31, 2018 and 2017, respectively. See Note D to the Condensed Consolidated Financial Statements.

[2] Amounts adjusted for rounding