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																12 Months Ended
		Apr. 30, 2015		Jan. 31, 2015		Oct. 31, 2014		Jul. 31, 2014		Apr. 30, 2014		Jan. 31, 2014		Oct. 31, 2013		Jul. 31, 2013		Apr. 30, 2015		Apr. 30, 2014		Apr. 30, 2013
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings		$ 2,578		$ 2,841		$ 1,175		$ 1,534		$ 2,568		$ 2,477		$ 3,693		$ 1,593		$ 8,128		$ 10,331		$ 10,411
Basic weighted average common shares outstanding																		28,283		27,636		27,173
Weighted Average Number of Shares Outstanding, Diluted																		28,614		28,111		27,629
Basic, EPS	[1]																	$ 0.29		$ 0.37		$ 0.38
Diluted, EPS		$ 0.09	[2]	$ 0.10	[2]	$ 0.04	[2]	$ 0.05	[2]	$ 0.09	[2]	$ 0.09	[2]	$ 0.13	[2]	$ 0.06	[2]	$ 0.28	[1],[2]	$ 0.37	[1],[2]	$ 0.38	[1]
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & Distributed Earnings, Class B Conversion																		$ 741		$ 961		$ 992
Reallocation of Undistributed Earnings																		4		(3)		4
Net earnings																		$ 745		$ 958		$ 996
Basic weighted average common shares outstanding																		2,587		2,587		2,587
Weighted Average Number of Shares Outstanding, Diluted																		2,587		2,587		2,587
Basic, EPS																		$ 0.29	[3]	$ 0.37	[3]	$ 0.38
Diluted, EPS																		$ 0.29	[3]	$ 0.37	[3]	$ 0.38

[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 $0.29, $0.37 and $0.38 for the years ended April 30, 2015, 2014 and 2013, 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