Property and Equipment (Details) (USD $)	3 Months Ended		9 Months Ended
	Apr. 27, 2013	Apr. 28, 2012	Apr. 27, 2013	Apr. 28, 2012	Jul. 28, 2012
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 497,402,000		$ 497,402,000		$ 435,872,000
Less: accumulated depreciation	(308,257,000)		(308,257,000)		(277,625,000)
Property and equipment, net	189,145,000		189,145,000		158,247,000
Depreciation and repairs and maintenance expenses [Abstract]
Depreciation expense	17,477	13,953	47,065	42,132
Repairs and maintenance expense	5,616	3,699	13,804	11,936
Land
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	3,479,000		3,479,000		2,915,000
Buildings
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	11,411,000		11,411,000		10,630,000
Leasehold Improvements
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	5,085,000		5,085,000		4,674,000
Vehicles
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	243,650,000		243,650,000		220,669,000
Computer hardware and software
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	63,740,000		63,740,000		57,965,000
Office furniture and equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	8,087,000		8,087,000		5,552,000
Equipment and machinery
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 161,950,000		$ 161,950,000		$ 133,467,000