Stock-Based Compensation Expense in Selling and Administrative Expenses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 31, 2015	Jan. 25, 2014	Jan. 31, 2015	Jan. 25, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 3,452	$ 2,466	$ 16,723	$ 8,147
Selling and Administrative Expenses | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	248	390	799	1,683
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	2,990	1,694	13,594	7,688
Selling and Administrative Expenses | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 214	$ 382	$ 2,330	$ (1,224)