Basic Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended
		Jul. 31, 2017	Jul. 31, 2016
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total	[1]	$ 0.09	$ 0.06
Basic weighted average common shares outstanding		29,671	28,938
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		(0.02)	(0.05)
Total	[2]	$ 0.09	$ 0.06
Distributed earnings		$ 3,014	$ 2,933
Undistributed earnings		(502)	(1,383)
Total		$ 2,512	$ 1,550
Basic weighted average common shares outstanding		27,307	26,457
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		(0.02)	(0.05)
Total	[2]	$ 0.09	$ 0.06
Distributed earnings		$ 256	$ 268
Undistributed earnings		(43)	(130)
Total		$ 213	$ 138
Basic weighted average common shares outstanding		2,364	2,481

[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 $0.09 and $0.06 for the three months ended July 31, 2017 and 2016, respectively. See Note D to the Condensed Consolidated Financial Statements.

[2] Amounts adjusted for rounding