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Stockholders' Equity - Schedule of Assumptions used in Valuing ESPP Purchases (Detail)
12 Months Ended
Apr. 30, 2017
Apr. 30, 2016
Apr. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate [1] 1.44% 0.93% 0.91%
Dividend yield [2] 0.00% 0.00% 0.00%
Employee Stock Purchase Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate 0.60% 0.19% 0.07%
Expected term 6 months 6 months 6 months
Expected volatility 45.30% 40.90% 38.20%
Dividend yield 0.00% 0.00% 0.00%
[1] The risk-free interest rate is based on the yield of a zero-coupon U.S. Treasury bill, commensurate with the three-year performance period.
[2] We do not expect to pay dividends in the foreseeable future.