Effective Income Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Schedule of Effective Tax Rate Reconciliation [Line Items]
Computed "expected" income tax expense	$ 3,641	$ 5,564	$ 5,434
Increase (decrease) in income taxes resulting from:
State income taxes, net of Federal income tax effect	269	493	568
Research and development credits	(516)	(258)	(584)
Change in valuation allowance for deferred tax assets	(5)	45	(187)
Tax contingencies	(955)	(47)	27
Other, net, including permanent items	(160)	(231)	(144)
Income tax expense	$ 2,274	$ 5,566	$ 5,114