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, 2016		Oct. 31, 2015	Oct. 31, 2016		Oct. 31, 2015
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings		$ 412		$ 2,153	$ 2,100		$ 4,725
Basic weighted average common shares outstanding		29,135		28,660	29,037		28,637
Weighted Average Number of Shares Outstanding, Diluted		29,548		28,941	29,398		28,910
Basic, EPS	[1]	$ 0.01		$ 0.08	$ 0.07		$ 0.16
Diluted, EPS	[1]	$ 0.01		$ 0.07	$ 0.07		$ 0.16
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & Distributed Earnings, Class B Conversion		$ 34		$ 194	$ 171		$ 426
Reallocation of Undistributed Earnings		4		1	5
Net earnings		$ 38		$ 195	$ 176		$ 426
Basic weighted average common shares outstanding		2,432		2,587	2,457		2,587
Weighted Average Number of Shares Outstanding, Diluted		2,432		2,587	2,457		2,587
Basic, EPS		$ 0.01	[2]	$ 0.08	$ 0.07	[2]	$ 0.16
Diluted, EPS		$ 0.01	[2]	$ 0.08	$ 0.07	[2]	$ 0.16

[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 $0.01 and $0.08 for the three months ended October 31, 2016 and 2015, and $0.07 and $0.16 for the six months ended October 31, 2016 and 2015, respectively. See Note D to the Condensed Consolidated Financial Statements.

[2] Amounts adjusted for rounding