Concentration of Credit Risk (Details) $ in Millions	3 Months Ended		12 Months Ended
	Jul. 30, 2016 USD ($) customer	Jul. 25, 2015 USD ($)	Jul. 30, 2016 USD ($) customer	Jul. 25, 2015 USD ($)	Jul. 26, 2014
Concentration Risk [Line Items]
Number of customers classified as highly concentrated | customer	5		5
Sales Revenue, Services, Net | Customer Concentration Risk | Five Unnamed Customers
Concentration Risk [Line Items]
Concentration risk percentage			69.70%	61.10%	58.30%
Sales Revenue, Services, Net | Customer Concentration Risk | AT&T Inc.
Concentration Risk [Line Items]
Concentration risk percentage			24.40%	20.80%	19.20%
Sales Revenue, Services, Net | Customer Concentration Risk | Verizon
Concentration Risk [Line Items]
Concentration risk percentage			11.00%	7.60%	8.20%
Sales Revenue, Services, Net | Customer Concentration Risk | Comcast
Concentration Risk [Line Items]
Concentration risk percentage			13.60%	12.90%	11.70%
Sales Revenue, Services, Net | Customer Concentration Risk | CenturyLink
Concentration Risk [Line Items]
Concentration risk percentage			14.50%	14.20%	13.80%
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | AT&T Inc.
Concentration Risk [Line Items]
Concentration risk percentage	20.30%	17.70%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 138.8	$ 101.7	$ 138.8	$ 101.7
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Windstream Corporation
Concentration Risk [Line Items]
Concentration risk percentage	11.50%	8.30%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 79.0	$ 47.8	79.0	47.8
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Another Customer
Concentration Risk [Line Items]
Concentration risk percentage	10.40%	11.20%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 71.5	$ 64.5	71.5	64.5
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Verizon
Concentration Risk [Line Items]
Concentration risk percentage	10.10%	8.90%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 69.0	$ 50.8	69.0	50.8
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Comcast
Concentration Risk [Line Items]
Concentration risk percentage	13.90%	11.00%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 95.3	$ 63.0	95.3	63.0
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | CenturyLink
Concentration Risk [Line Items]
Concentration risk percentage	11.50%	14.00%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 79.0	$ 80.1	$ 79.0	$ 80.1