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			9 Months Ended
		Jan. 31, 2017		Jan. 31, 2016	Jan. 31, 2017		Jan. 31, 2016
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings		$ 2,243		$ 2,111	$ 4,343		$ 6,836
Basic weighted average common shares outstanding		29,333		28,778	29,136		28,684
Weighted Average Number of Shares Outstanding, Diluted		29,630		29,107	29,447		28,973
Basic, EPS	[1]	$ 0.08		$ 0.07	$ 0.15		$ 0.24
Diluted, EPS	[1]	$ 0.08		$ 0.07	$ 0.15		$ 0.24
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & Distributed Earnings, Class B Conversion		$ 187		$ 189	$ 356		$ 615
Reallocation of Undistributed Earnings		2		1	6		2
Net earnings		$ 189		$ 190	$ 362		$ 617
Basic weighted average common shares outstanding		2,432		2,587	2,448		2,587
Weighted Average Number of Shares Outstanding, Diluted		2,432		2,587	2,448		2,587
Basic, EPS		$ 0.08	[2]	$ 0.07	$ 0.15	[2]	$ 0.24
Diluted, EPS		$ 0.08	[2]	$ 0.07	$ 0.15	[2]	$ 0.24

[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 $0.08 and $0.07 for the three months ended January 31, 2017 and 2016, and $0.15 and $0.24 for the nine months ended January 31, 2017 and 2016, respectively. See Note D to the Condensed Consolidated Financial Statements.

[2] Amounts adjusted for rounding