Schedule of Quarterly Results (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
Quarterly Financial Data [Line Items]
Total revenues	$ 25,925		$ 24,427		$ 26,931		$ 23,318		$ 25,214		$ 23,076		$ 26,263		$ 25,914		$ 100,601		$ 100,467		$ 102,636
Gross margin	15,242		13,963		15,526		12,155		14,185		12,032		14,680		14,010		56,886		54,907		56,796
Operating income	3,211		3,539		5,392		2,383		3,536		2,291		4,236		3,721		14,525		13,784		16,168
Net earnings	$ 2,568		$ 2,477		$ 3,693		$ 1,593		$ 3,078		$ 2,140		$ 2,771		$ 2,422		$ 10,331		$ 10,411		$ 11,343
Diluted earnings per share	$ 0.09	[1]	$ 0.09	[1]	$ 0.13	[1]	$ 0.06	[1]	$ 0.11	[1]	$ 0.08	[1]	$ 0.10	[1]	$ 0.09	[1]	$ 0.37	[1],[2]	$ 0.38	[1],[2]	$ 0.42	[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 $0.37, $0.38 and $0.43 for the years ended April 30, 2014, 2013 and 2012, respectively. See Note 1 to the Consolidated Financial Statements.