Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	6 Months Ended
	Jan. 23, 2016	Jul. 25, 2015
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangible Assets Gross Excluding Goodwill	$ 231,540	$ 216,986
Accumulated amortization:	102,109	96,060
Intangible assets, net	129,431	120,926
Finite-Lived Intangible Assets, Period Increase (Decrease)	$ 3,400
Customer relationships
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Weighted average remaining useful lives (in years)	11 years 7 months 16 days
Carrying amount	$ 211,575	195,375
Accumulated amortization:	$ 92,079	83,772
Contract backlog
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Weighted average remaining useful lives (in years)	10 months 24 days
Carrying amount	$ 4,780	8,076
Accumulated amortization:	$ 4,472	7,381
Trade names
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Weighted average remaining useful lives (in years)	6 years 11 months 15 days
Carrying amount	$ 9,800	8,200
Accumulated amortization:	$ 5,337	4,650
Non-compete agreements
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Weighted average remaining useful lives (in years)	2 years 10 months 17 days
Carrying amount	$ 685	635
Accumulated amortization:	221	257
UtiliQuest
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
UtiliQuest trade name	$ 4,700	$ 4,700