Acquisitions (Details) $ in Millions	3 Months Ended
	Oct. 24, 2015 USD ($)	Jul. 25, 2015 USD ($)	Oct. 25, 2014 USD ($) business
TelCom Construction, Inc.
Business Acquisition [Line Items]
Payment to acquire business, net of cash acquired	$ 48.8
Hewitt Power & Communications, Inc
Business Acquisition [Line Items]
Payment to acquire business, net of cash acquired			$ 8.0
Cable Installation Contractors
Business Acquisition [Line Items]
Payment to acquire business, net of cash acquired			$ 1.5
Number of businesses acquired | business			2
Moll's Utility Services, LLC
Business Acquisition [Line Items]
Payment to acquire business, net of cash acquired		$ 6.5
Venture Communications Group, LLC
Business Acquisition [Line Items]
Payment to acquire business, net of cash acquired		$ 15.6