Concentration of Credit Risk (Details) $ in Millions	3 Months Ended
	Oct. 29, 2016 USD ($) customer	Jul. 30, 2016 USD ($)	Oct. 24, 2015
Concentration Risk [Line Items]
Number of customers classified as highly concentrated | customer	5
Sales Revenue, Services, Net | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk percentage	10.00%
Sales Revenue, Services, Net | Customer Concentration Risk | Five Unnamed Customers
Concentration Risk [Line Items]
Concentration risk percentage	74.90%		64.90%
Sales Revenue, Services, Net | Customer Concentration Risk | AT&T Inc.
Concentration Risk [Line Items]
Concentration risk percentage	29.00%		19.10%
Sales Revenue, Services, Net | Customer Concentration Risk | Comcast
Concentration Risk [Line Items]
Concentration risk percentage	15.70%		15.60%
Sales Revenue, Services, Net | Customer Concentration Risk | CenturyLink
Concentration Risk [Line Items]
Concentration risk percentage	15.10%		12.00%
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk percentage	10.00%
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | AT&T Inc.
Concentration Risk [Line Items]
Concentration risk percentage	22.90%	20.30%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 183.5	$ 138.8
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Windstream Corporation
Concentration Risk [Line Items]
Concentration risk percentage	11.40%	11.50%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 90.9	$ 79.0
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Another Customer
Concentration Risk [Line Items]
Concentration risk percentage	9.00%	10.40%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 72.1	$ 71.5
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Verizon
Concentration Risk [Line Items]
Concentration risk percentage	10.00%	10.10%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 80.1	$ 69.0
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Comcast
Concentration Risk [Line Items]
Concentration risk percentage	14.60%	13.90%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 117.0	$ 95.3
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | CenturyLink
Concentration Risk [Line Items]
Concentration risk percentage	13.50%	11.50%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 108.3	$ 79.0