Concentration of Credit Risk (Details) $ in Millions	12 Months Ended
	Jul. 25, 2015 USD ($) customer	Jul. 26, 2014 USD ($)	Jul. 27, 2013
Concentration Risk [Line Items]
Number of customers classified as highly concentrated | customer	5
Customer Concentration Risk | Five Unnamed Customers
Concentration Risk [Line Items]
Concentration risk percentage	61.10%	58.30%	58.50%
Sales Revenue, Services, Net | Customer Concentration Risk | AT&T Inc.
Concentration Risk [Line Items]
Concentration risk percentage	20.80%	19.20%	15.50%
Sales Revenue, Services, Net | Customer Concentration Risk | CenturyLink, Inc.
Concentration Risk [Line Items]
Concentration risk percentage	14.20%	13.80%	14.60%
Sales Revenue, Services, Net | Customer Concentration Risk | Comcast Corporation
Concentration Risk [Line Items]
Concentration risk percentage	12.90%	11.70%	10.90%
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | AT&T Inc.
Concentration Risk [Line Items]
Concentration risk percentage	17.70%	17.90%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 101.7	$ 87.6
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | CenturyLink, Inc.
Concentration Risk [Line Items]
Concentration risk percentage	14.00%	9.80%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 80.1	$ 48.2
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Comcast Corporation
Concentration Risk [Line Items]
Concentration risk percentage	11.00%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 63.0
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Another Customer
Concentration Risk [Line Items]
Concentration risk percentage	11.20%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 64.5