Concentration of Credit Risk (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Oct. 26, 2013	Oct. 27, 2012	Jul. 27, 2013
Concentration Risk [Line Items]
Number of customers classified as highly concentrated	5
Customer Concentration Risk | Five Unnamed Customers
Concentration Risk [Line Items]
Concentration risk percentage	57.20%	59.60%
Sales Revenue, Services, Net | Customer Concentration Risk | AT&T
Concentration Risk [Line Items]
Concentration risk percentage	17.50%	13.50%
Sales Revenue, Services, Net | Customer Concentration Risk | CenturyLink
Concentration Risk [Line Items]
Concentration risk percentage	15.50%	13.70%
Sales Revenue, Services, Net | Customer Concentration Risk | Comcast
Concentration Risk [Line Items]
Concentration risk percentage	10.50%	12.70%
Sales Revenue, Services, Net | Customer Concentration Risk | Verizon
Concentration Risk [Line Items]
Concentration risk percentage	8.40%	10.20%
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | AT&T
Concentration Risk [Line Items]
Concentration risk percentage	13.10%	12.60%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 69.0		$ 57.4
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | CenturyLink
Concentration Risk [Line Items]
Concentration risk percentage	12.60%	13.70%
Accounts receivable, costs, and estimated earnings in excess of billings	66.5		62.6
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Windstream Corporation
Concentration Risk [Line Items]
Concentration risk percentage	9.80%	13.00%
Accounts receivable, costs, and estimated earnings in excess of billings	51.4		59.4
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Verizon
Concentration Risk [Line Items]
Concentration risk percentage	10.40%	7.30%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 54.8		$ 33.4