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Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $)
In Thousands, unless otherwise specified
Jul. 31, 2013
Apr. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents $ 45,869 $ 37,716
Marketable securities 19,888 24,763
Total 65,757 62,479
Quoted Prices in Active Markets for Identical Assets, Level 1
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents 45,869 37,716
Marketable securities 7,466 11,215
Total 53,335 48,931
Significant Other Observable Inputs, Level 2
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 12,422 13,548
Total $ 12,422 $ 13,548