Diluted Earnings Per Share for Class B Common Shares Using Two-Class Method (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Oct. 31, 2013		Oct. 31, 2012		Oct. 31, 2013		Oct. 31, 2012
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings	$ 3,693		$ 2,771		$ 5,286		$ 5,193
Basic weighted average common shares outstanding	27,448		27,151		27,406		27,112
Weighted Average Number of Shares Outstanding, Diluted	27,874		27,627		27,841		27,596
Basic, EPS	$ 0.13	[1]	$ 0.10	[1]	$ 0.19	[1]	$ 0.19	[1]
Diluted, EPS	$ 0.13	[1]	$ 0.10	[1]	$ 0.19	[1]	$ 0.19	[1]
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & distributed earnings, Class B Conversion	348		264		498		495
Reallocation of Undistributed Earnings	(1)		(1)		(4)		(1)
Net earnings	$ 347		$ 263		$ 494		$ 494
Basic weighted average common shares outstanding	2,587		2,587		2,587		2,587
Weighted Average Number of Shares Outstanding, Diluted	2,587		2,587		2,587		2,587
Basic, EPS	$ 0.13		$ 0.10		$ 0.19		$ 0.19
Diluted, EPS	$ 0.13		$ 0.10		$ 0.19		$ 0.19

[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 $0.13 and $0.10 for the three months ended October 31, 2013 and 2012 and $0.19 for the six months ended October 31, 2013 and 2012, respectively. See Note D to the Condensed Consolidated Financial Statements.