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Concentration of Credit Risk (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Jul. 26, 2014
Jul. 27, 2013
Jul. 28, 2012
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 58.30% 58.50% 59.60%
Sales Revenue, Services, Net | Customer Concentration Risk | AT&T
      
Concentration Risk [Line Items]      
Concentration risk percentage 19.20% 15.50% 13.70%
Sales Revenue, Services, Net | Customer Concentration Risk | CenturyLink
      
Concentration Risk [Line Items]      
Concentration risk percentage 13.80% 14.60% 13.60%
Sales Revenue, Services, Net | Customer Concentration Risk | Comcast
      
Concentration Risk [Line Items]      
Concentration risk percentage 11.70% 10.90% 12.60%
Sales Revenue, Services, Net | Customer Concentration Risk | Verizon
      
Concentration Risk [Line Items]      
Concentration risk percentage 8.20% 9.60% 11.30%
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | AT&T
      
Concentration Risk [Line Items]      
Concentration risk percentage 17.90% 12.60%  
Accounts receivable, costs, and estimated earnings in excess of billings $ 87.6 $ 57.4  
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | CenturyLink
      
Concentration Risk [Line Items]      
Concentration risk percentage 9.80% 13.70%  
Accounts receivable, costs, and estimated earnings in excess of billings 48.2 62.6  
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Windstream Corporation
      
Concentration Risk [Line Items]      
Concentration risk percentage 8.90% 13.00%  
Accounts receivable, costs, and estimated earnings in excess of billings $ 43.6 $ 59.4