Earnings Per Common share - 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, 2018	Jul. 31, 2017
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Basic weighted average common shares outstanding		30,725	29,671
Weighted Average Number of Shares Outstanding, Diluted		31,343	29,989
Basic, EPS	[1]	$ 0.05	$ 0.09
Diluted, EPS	[1]	$ 0.04	$ 0.09
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & Distributed Earnings, Per Basic		$ 86	$ 213
Reallocation of undistributed earnings from Class A Common Shares to Class B Common Shares		2
Net earnings		$ 88	$ 213
Basic weighted average common shares outstanding		1,911	2,364
Weighted Average Number of Shares Outstanding, Diluted		1,911	2,364
Basic, EPS	[2]	$ 0.05	$ 0.09
Diluted, EPS	[2]	$ 0.05	$ 0.09

[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