Acquisitions (Details) $ / shares in Units, $ in Thousands	3 Months Ended						12 Months Ended
	Jul. 25, 2015 USD ($)	Jan. 24, 2015 USD ($) business	Oct. 25, 2014 USD ($)	Jul. 26, 2014 USD ($)	Apr. 26, 2014 USD ($)	Jul. 27, 2013 USD ($)	Jul. 25, 2015 USD ($)	Jul. 26, 2014 USD ($)	Jul. 27, 2013 USD ($) $ / shares	Dec. 03, 2012 USD ($)
Business Acquisition [Line Items]
Goodwill acquisitions							$ 2,188	$ 1,278
Goodwill	$ 271,653			$ 269,088		$ 267,810	271,653	$ 269,088	$ 267,810
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles							$ 22,000
Business acquisition, cost of acquired entity, cash paid for other items						3,800			3,800
Hewitt Power & Communications, Inc
Business Acquisition [Line Items]
Payment to acquire business, net of cash acquired			$ 8,000
Cable Installation Contractors
Business Acquisition [Line Items]
Payment to acquire business, net of cash acquired		$ 1,500
Number of businesses acquired | business		2
Moll's Utility Services, LLC
Business Acquisition [Line Items]
Payment to acquire business, net of cash acquired	6,500
Venture Communications Group, LLC
Business Acquisition [Line Items]
Payment to acquire business, net of cash acquired	$ 15,600
Telecommunications Specialty Construction Contractor, Canada [Member]
Business Acquisition [Line Items]
Payment to acquire business, net of cash acquired					$ 700
Watts Brothers
Business Acquisition [Line Items]
Payment to acquire business, net of cash acquired				$ 16,400
Telecommunications Infrastructure Services Subsidiaries of Quanta Services, Inc [Member]
Business Acquisition [Line Items]
Business acquisition, cost of acquired entity, cash paid less working capital received and other items										$ 275,000
Business acquisition, cost of acquired entity, cash paid for working capital										40,400
Business acquisition, cost of acquired entity, cash paid for other items										$ 3,700
Pro forma contract revenue									1,837,000
Pro forma income before taxes									90,000
Pro forma net income									$ 54,400
Business Acquisition, Pro Forma Earnings Per Share, Basic | $ / shares									$ 1.65
Business Acquisition, Pro Forma Earnings Per Share, Diluted | $ / shares									$ 1.61
Sage Telecommunications Corp of Colorado, LLC
Business Acquisition [Line Items]
Payment to acquire business, net of cash acquired						$ 11,300