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Stockholders' Equity - Summary of Stock Compensation Expense (Detail) - USD ($)
$ in Thousands
12 Months Ended
Apr. 30, 2017
Apr. 30, 2016
Apr. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense $ 8,590 $ 6,472 $ 5,808
Cost of sales      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense 1,139 564 520
Research and development      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense 217 169 139
Selling and marketing      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense 801 494 379
General and administrative      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense $ 6,433 $ 5,245 $ 4,770