Stockholders' Equity - Summary of Stock Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2020		Apr. 30, 2019	Apr. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 2,921		$ 7,992	$ 7,815
Cost of sales
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	704		746	882
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	121		99	187
Selling and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	340		489	382
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,756	[1]	$ 6,658	$ 6,364

[1] The decrease in general and administrative stock-based compensation expense from fiscal 2019 was because of the separation of our former President and Chief Executive Officer.