Schedule of Quarterly Results (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2017		Apr. 30, 2016		Apr. 30, 2015
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 26,266	$ 26,441	$ 26,146	$ 27,433	$ 28,866	$ 27,095	$ 29,070	$ 28,858	$ 106,286		$ 113,889		$ 102,873
Gross margin	14,340	14,049	13,018	13,796	15,839	13,607	14,897	15,317	55,202		59,660		52,414
Operating income	2,957	2,455	708	1,646	3,861	2,518	3,328	3,820	7,766		13,527		9,342
Net earnings	$ 10,278	$ 2,243	$ 412	$ 1,688	$ 3,406	$ 2,111	$ 2,153	$ 2,572	$ 14,621		$ 10,242		$ 8,128
Diluted earnings per share	$ 0.34	$ 0.08	$ 0.01	$ 0.06	$ 0.12	$ 0.07	$ 0.07	$ 0.09	$ 0.49	[1]	$ 0.35	[1]	$ 0.28	[1]

[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 $0.49, $0.35 and $0.29 for the years ended April 30, 2017, 2016 and 2015, respectively. See Note 1 to the Consolidated Financial Statements.