Stock-Based Compensation Expense in Selling and Administrative Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 26, 2019	Jan. 27, 2018	Jan. 26, 2019	Jan. 27, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 1,388	$ 1,656	$ 3,091	$ 4,788
Selling and Administrative Expenses | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	284	250	701	697
Selling and Administrative Expenses | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	679	1,032	1,767	3,020
Selling and Administrative Expenses | Performance Stock Unit
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 425	$ 374	$ 623	$ 1,071