Schedule of Quarterly Results (Detail) - USD ($) $ / shares in Units, $ 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
Schedule Of Quarterly Financial Data [Line Items]
Total revenues	$ 27,600		$ 25,839		$ 24,577		$ 24,857		$ 25,925		$ 24,427		$ 26,931		$ 23,318		$ 102,873		$ 100,601		$ 100,467
Gross margin	14,124		12,849		12,096		13,345		15,242		13,963		15,526		12,155		52,414		56,886		54,907
Operating income	3,425		2,375		1,379		2,163		3,211		3,539		5,392		2,383		9,342		14,525		13,784
Net earnings	$ 2,578		$ 2,841		$ 1,175		$ 1,534		$ 2,568		$ 2,477		$ 3,693		$ 1,593		$ 8,128		$ 10,331		$ 10,411
Diluted earnings per share	$ 0.09	[1]	$ 0.10	[1]	$ 0.04	[1]	$ 0.05	[1]	$ 0.09	[1]	$ 0.09	[1]	$ 0.13	[1]	$ 0.06	[1]	$ 0.28	[1],[2]	$ 0.37	[1],[2]	$ 0.38	[2]

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

[2] 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.