Summary of Fair Value of Financial Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2014	Apr. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 24,704	$ 31,934
Short-term investments	67,898	40,700
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	3,030	7,213
Restricted cash	500	604
Short-term investments	67,898	40,700
Total assets	71,428	48,517
Fair Value, Measurements, Recurring | Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		242
Short-term investments	7,224	7,474
Fair Value, Measurements, Recurring | Municipal Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	887
Short-term investments	3,407
Fair Value, Measurements, Recurring | Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	5,996
Fair Value, Measurements, Recurring | US Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	701
Short-term investments	51,271	33,226
Fair Value, Measurements, Recurring | Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	1,442	6,971
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	2,143	7,213
Restricted cash	500	604
Short-term investments	51,271	33,226
Total assets	53,914	41,043
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		242
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | US Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	701
Short-term investments	51,271	33,226
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	1,442	6,971
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	887
Short-term investments	16,627	7,474
Total assets	17,514	7,474
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	7,224	7,474
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Municipal Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	887
Short-term investments	3,407
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 5,996