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		6 Months Ended
		Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Basic weighted average common shares outstanding		30,926	29,906	30,825	29,788
Weighted Average Number of Shares Outstanding, Diluted		31,477	30,229	31,412	30,110
Basic, EPS	[1]	$ 0.04	$ 0.08	$ 0.09	$ 0.17
Diluted, EPS	[1]	$ 0.04	$ 0.08	$ 0.08	$ 0.17
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & Distributed Earnings, Per Basic		$ 76	$ 184	$ 159	$ 396
Reallocation of undistributed earnings from Class A Common Shares to Class B Common Shares		2			1
Net earnings		$ 78	$ 184	$ 159	$ 397
Basic weighted average common shares outstanding		1,822	2,317	1,866	2,340
Weighted Average Number of Shares Outstanding, Diluted		1,822	2,317	1,866	2,340
Basic, EPS	[2]	$ 0.04	$ 0.08	$ 0.09	$ 0.17
Diluted, EPS	[2]	$ 0.04	$ 0.08	$ 0.09	$ 0.17

[1] 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 $0.08 for the three months ended October 31, 2018 and 2017, and $0.09 and $0.17 for the six months ended October 31, 2018 and 2017, respectively. See Note D to the Condensed Consolidated Financial Statements.

[2] Amounts adjusted for rounding