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																12 Months Ended
	Apr. 30, 2014		Jan. 31, 2014		Oct. 31, 2013		Jul. 31, 2013		Apr. 30, 2013		Jan. 31, 2013		Oct. 31, 2012		Jul. 31, 2012		Apr. 30, 2014		Apr. 30, 2013		Apr. 30, 2012
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings	$ 2,568		$ 2,477		$ 3,693		$ 1,593		$ 3,078		$ 2,140		$ 2,771		$ 2,422		$ 10,331		$ 10,411		$ 11,343
Basic weighted average common shares outstanding																	27,636		27,173		26,455
Weighted Average Number of Shares Outstanding, Diluted																	28,111		27,629		27,098
Basic, EPS																	$ 0.37	[1]	$ 0.38	[1]	$ 0.43	[1]
Diluted, EPS	$ 0.09	[2]	$ 0.09	[2]	$ 0.13	[2]	$ 0.06	[2]	$ 0.11	[2]	$ 0.08	[2]	$ 0.10	[2]	$ 0.09	[2]	$ 0.37	[1],[2]	$ 0.38	[1],[2]	$ 0.42	[1]
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & distributed earnings, Class B Conversion																	961		992		1,106
Reallocation of Undistributed Earnings																	(3)		4		(4)
Net earnings																	$ 958		$ 996		$ 1,102
Basic weighted average common shares outstanding																	2,587		2,587		2,615
Weighted Average Number of Shares Outstanding, Diluted																	2,587		2,587		2,615
Basic, EPS																	$ 0.37	[3]	$ 0.38	[3]	$ 0.43	[3]
Diluted, EPS																	$ 0.37	[3]	$ 0.38	[3]	$ 0.43	[3]

[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 per share for Class B shares under the two-class method are $0.37, $0.38 and $0.43 for the years ended April 30, 2014, 2013 and 2012, respectively. See Note 1 to the Consolidated Financial Statements.

[2] Quarterly amounts may not sum to full year total due to rounding.

[3] Amounts adjusted for rounding