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, 2015		Jan. 31, 2014		Jan. 31, 2015		Jan. 31, 2014
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings	$ 2,841		$ 2,477		$ 5,550		$ 7,763
Basic weighted average common shares outstanding	28,239		27,686		28,247		27,499
Weighted Average Number of Shares Outstanding, Diluted	28,554		28,187		28,580		27,972
Basic, EPS	$ 0.10	[1]	$ 0.09	[1]	$ 0.20	[1]	$ 0.28	[1]
Diluted, EPS	$ 0.10	[1]	$ 0.09	[1]	$ 0.19	[1]	$ 0.28	[1]
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & Distributed Earnings, Class B Conversion	261		230		508		727
Reallocation of Undistributed Earnings (loss)	(1)		1		3		(4)
Net earnings	$ 260		$ 231		$ 511		$ 723
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	$ 0.10		$ 0.09		$ 0.20		$ 0.28
Diluted, EPS	$ 0.10		$ 0.09		$ 0.20		$ 0.28

[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 $0.10 and $0.09 for the three months ended January 31, 2015 and 2014 and $0.20 and $0.28 for the nine months ended January 31, 2015 and 2014, respectively. See Note D to the Condensed Consolidated Financial Statements.