Diluted Earnings Per Share for Class B Common Shares Using Two-Class Method (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended
		Jul. 31, 2017	Jul. 31, 2016
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Basic weighted average common shares outstanding		29,671	28,938
Weighted Average Number of Shares Outstanding, Diluted		29,989	29,254
Basic, EPS	[1]	$ 0.09	$ 0.06
Diluted, EPS	[1]	$ 0.09	$ 0.06
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & Distributed Earnings, Per Basic		$ 213	$ 138
Reallocation of Undistributed Earnings			2
Net earnings		$ 213	$ 140
Basic weighted average common shares outstanding		2,364	2,481
Weighted Average Number of Shares Outstanding, Diluted		2,364	2,481
Basic, EPS	[2]	$ 0.09	$ 0.06
Diluted, EPS	[2]	$ 0.09	$ 0.06

[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