Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Apr. 23, 2016	Apr. 25, 2015	Apr. 23, 2016	Apr. 25, 2015	Aug. 07, 2015	Jul. 25, 2015
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Goodwill	$ 281,448		$ 281,448			$ 271,653
Amortization expense for finite-lived intangible assets	4,500	$ 4,100	14,000	$ 12,400
Customer relationships
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Carrying amount	211,575		211,575			195,375
Trade names
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Carrying amount	9,800		9,800			8,200
Non-compete agreements
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Carrying amount	685		685			$ 635
TelCom Construction, Inc.
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Goodwill					$ 9,700
TelCom Construction, Inc. | Customer relationships
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Carrying amount	16,200		16,200
TelCom Construction, Inc. | Trade names
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Carrying amount	1,600		1,600
TelCom Construction, Inc. | Non-compete agreements
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Carrying amount	$ 200		$ 200