Effective Income Tax Rate (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Schedule of Effective Tax Rate Reconciliation [Line Items]
Computed "expected" income tax expense	$ 5,564	$ 5,434	$ 6,045
Increase (decrease) in income taxes resulting from:
State income taxes, net of Federal income tax effect	493	568	405
Research and development credits	(258)	(584)	(259)
Change in valuation allowance for deferred tax assets	45	(187)	34
Tax contingencies	(47)	27	(59)
Other, net, including permanent items	(231)	(144)	(238)
Income tax expense	$ 5,566	$ 5,114	$ 5,928