Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	Jan. 27, 2018	Jul. 29, 2017	Jul. 30, 2016
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 315,217	$ 315,217	$ 309,920
Accumulated Amortization	143,748	131,656	112,041
Intangible Assets, Net	171,469	183,561	197,879
UtiliQuest
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	4,700	4,700	4,700
Accumulated Amortization	0	0	0
Intangible Assets, Net	4,700	4,700	4,700
Customer relationships
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	299,717	299,717	289,955
Accumulated Amortization	135,544	124,084	101,012
Intangible Assets, Net	164,173	175,633	188,943
Trade names
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	10,350	10,350	9,800
Accumulated Amortization	7,872	7,285	6,034
Intangible Assets, Net	2,478	3,065	3,766
Non-compete agreements
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	450	450	685
Accumulated Amortization	332	287	329
Intangible Assets, Net	$ 118	$ 163	356
Contract backlog
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)			4,780
Accumulated Amortization			4,666
Intangible Assets, Net			$ 114