Accrued Insurance Claims - Narratives (Details)	6 Months Ended	12 Months Ended
	Jan. 27, 2018 USD ($) state	Jul. 29, 2017 USD ($)	Jul. 30, 2016 USD ($)	Jul. 25, 2015 USD ($)
Accrued Insurance Claims [Line Items]
Number of states with state-sponsored insurance fund | state	2
Aggregate stop loss coverage for automobile liability, general liability, and workers' compensation claims before adjustment	$ 67,100,000	$ 103,700,000	$ 84,600,000
Insurance liability, annual retained risk loss	400,000			$ 250,000
Losses Incurred but not Recognized from Insurance Claims	53,300,000	$ 50,000,000	$ 45,000,000
Maximum
Accrued Insurance Claims [Line Items]
Retained risk of loss, general liability and workers' compensation, maximum automobile liability	$ 1,000,000