Property and Equipment (Details) - USD ($) $ in Thousands	6 Months Ended
	Jan. 27, 2018	Jul. 29, 2017	Jul. 30, 2016
Property, Plant and Equipment [Line Items]
Total	$ 968,822	$ 935,273	$ 781,493
Less: accumulated depreciation	(554,054)	(513,166)	(454,823)
Property and equipment, net	414,768	422,107	326,670
Land
Property, Plant and Equipment [Line Items]
Total	3,470	3,470	3,475
Buildings
Property, Plant and Equipment [Line Items]
Total	$ 12,315	12,073	11,969
Buildings | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (Years)	10 years
Buildings | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (Years)	35 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total	$ 14,202	13,912	13,753
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (Years)	1 year
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (Years)	10 years
Vehicles
Property, Plant and Equipment [Line Items]
Total	$ 536,379	496,820	404,273
Vehicles | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (Years)	1 year
Vehicles | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (Years)	5 years
Computer hardware and software
Property, Plant and Equipment [Line Items]
Total	$ 117,058	107,779	95,570
Computer hardware and software | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (Years)	1 year
Computer hardware and software | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (Years)	7 years
Office furniture and equipment
Property, Plant and Equipment [Line Items]
Total	$ 11,686	12,226	10,374
Office furniture and equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (Years)	1 year
Office furniture and equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (Years)	10 years
Equipment and machinery
Property, Plant and Equipment [Line Items]
Total	$ 273,712	$ 288,993	$ 242,079
Equipment and machinery | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (Years)	1 year
Equipment and machinery | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives (Years)	10 years