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				9 Months Ended
	Jan. 31, 2013		Jan. 31, 2012		Jan. 31, 2013		Jan. 31, 2012
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings	$ 2,140		$ 2,592		$ 7,333		$ 7,862
Basic weighted average common shares outstanding	27,193		26,531		27,139		26,308
Weighted Average Number of Shares Outstanding, Diluted	27,614		27,271		27,601		26,959
Basic, EPS	$ 0.08	[1]	$ 0.10	[1]	$ 0.27	[1]	$ 0.30	[1]
Diluted, EPS	$ 0.08	[1]	$ 0.10	[1]	$ 0.27	[1]	$ 0.29	[1]
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & distributed earnings, Class B Conversion	204		251		698		770
Basic, EPS							$ 0.29
Reallocation of Undistributed Earnings	9		(1)		9		(2)
Net earnings	$ 213		$ 250		$ 707		$ 768
Basic weighted average common shares outstanding	2,587		2,587		2,587		2,624
Weighted Average Number of Shares Outstanding, Diluted	2,587		2,587		2,587		2,624
Basic, EPS	$ 0.08		$ 0.10		$ 0.27		$ 0.30
Diluted, EPS	$ 0.08		$ 0.10		$ 0.27		$ 0.29

[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 $0.10 for the three months ended January 31, 2013 and 2012 and $0.27 and $0.29 for the nine months ended January 31, 2013 and 2012, respectively. See Note D to the Condensed Consolidated Financial Statements.