Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 28, 2017	Jan. 23, 2016	Jan. 28, 2017	Jan. 23, 2016	Jul. 30, 2016
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangible Assets Gross Excluding Goodwill	$ 304,952		$ 304,952		$ 309,920
Accumulated amortization:	119,384		119,384		112,041
Intangible assets, net	185,568		185,568		197,879
Decrease in intangible assets	4,800
Amortization of intangible assets	$ 6,100	$ 4,700	12,300	$ 9,500
Customer relationships
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Weighted average remaining useful lives (in years)	12 years 4 months 1 day
Carrying amount	$ 289,917		289,917		289,955
Accumulated amortization:	$ 112,395		112,395		101,012
Contract backlog
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Weighted average remaining useful lives (in years)	0 years
Carrying amount	$ 0		0		4,780
Accumulated amortization:	$ 0		0		4,666
Trade names
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Weighted average remaining useful lives (in years)	7 years 7 months 1 day
Carrying amount	$ 9,650		9,650		9,800
Accumulated amortization:	$ 6,556		6,556		6,034
Non-compete agreements
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Weighted average remaining useful lives (in years)	2 years 5 months 1 day
Carrying amount	$ 685		685		685
Accumulated amortization:	433		433		329
UtiliQuest
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
UtiliQuest trade name	$ 4,700		$ 4,700		$ 4,700