Summary of Cash and Cash Equivalents (Detail) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2013	Apr. 30, 2012
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 25,045	$ 74,367
U.S. Treasury securities
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	7,209	7,499
Corporate bonds
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents		21,219
Demand deposit accounts
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	16,522	45,361
Money market funds
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 1,314	$ 288