Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Oct. 29, 2016	Oct. 24, 2015	Jul. 30, 2016
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangible Assets Gross Excluding Goodwill	$ 309,732		$ 309,920
Accumulated amortization:	118,068		112,041
Intangible assets, net	191,664		197,879
Amortization of intangible assets	$ 6,200	$ 4,800
Customer relationships
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Weighted average remaining useful lives (in years)	12 years 6 months
Carrying amount	$ 289,917		289,955
Accumulated amortization:	$ 106,716		101,012
Contract backlog
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Weighted average remaining useful lives (in years)	1 month
Carrying amount	$ 4,780		4,780
Accumulated amortization:	$ 4,751		4,666
Trade names
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Weighted average remaining useful lives (in years)	7 years 4 months
Carrying amount	$ 9,650		9,800
Accumulated amortization:	$ 6,220		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
Carrying amount	$ 685		685
Accumulated amortization:	381		329
UtiliQuest
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
UtiliQuest trade name	$ 4,700		$ 4,700