Summary of Cash and Cash Equivalents (Detail) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2013	Apr. 30, 2013
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 26,740	$ 25,045
U.S. Treasury securities
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents		7,209
Demand deposit accounts
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	21,486	16,522
Money Market Funds
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 5,254	$ 1,314