Property and Equipment (Details) (USD $)	3 Months Ended		6 Months Ended
	Jan. 26, 2013	Jan. 28, 2012	Jan. 26, 2013	Jan. 28, 2012	Jul. 28, 2012
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 483,117,000		$ 483,117,000		$ 435,872,000
Less: accumulated depreciation	(295,875,000)		(295,875,000)		(277,625,000)
Property and equipment, net	187,242,000		187,242,000		158,247,000
Depreciation and repairs and maintenance expenses [Abstract]
Depreciation expense	15,868	13,911	29,588	28,179
Repairs and maintenance expense	4,376	3,704	8,188	8,237
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	5,039,000		5,039,000		4,674,000
Vehicles
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	235,496,000		235,496,000		220,669,000
Computer hardware and software
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	62,156,000		62,156,000		57,965,000
Office furniture and equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	7,203,000		7,203,000		5,552,000
Equipment and machinery
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 158,333,000		$ 158,333,000		$ 133,467,000