Pension and Other Postretirement Benefit Plans - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended
	Jan. 31, 2015 Employee	Aug. 02, 2014	Jan. 25, 2014	Jan. 31, 2015 Employee	Jan. 25, 2014
Pension and Other Postretirement Benefit Plans [Line Items]
Pension expense	$ 7,914		$ 582	$ 9,299	$ 1,913
Increase in pension liability		15,747		5,498
Increase (decrease) in other comprehensive income, before tax		15,747		(7,619)
Pension plan, expected termination period				18 months
Pension plan, expected termination period				24 months
Number of terminated vested participants elected to receive lump sum payments	735
Lump sum payments made to plan participants	15,190
Number of remaining active and terminated vested participants elected to receive lump sum payments				2,300
Company contributions, employee benefit expenses	3,574		3,848	12,049	12,384
Company contributions for postretirement plan	38		38	113	113
Selling and Administrative Expenses
Pension and Other Postretirement Benefit Plans [Line Items]
Pension plan settlement charge	$ 7,271