Concentration of Credit Risk (Details) (USD $) In Millions, unless otherwise specified		6 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended					6 Months Ended			6 Months Ended
	Jan. 25, 2014 Customers	Jan. 25, 2014 Customer Concentration Risk Five Unnamed Customers	Jan. 25, 2014 Sales Revenue, Services, Net Customer Concentration Risk AT&T	Jan. 26, 2013 Sales Revenue, Services, Net Customer Concentration Risk AT&T	Jan. 25, 2014 Sales Revenue, Services, Net Customer Concentration Risk AT&T	Jan. 26, 2013 Sales Revenue, Services, Net Customer Concentration Risk AT&T	Jan. 25, 2014 Sales Revenue, Services, Net Customer Concentration Risk CenturyLink	Jan. 26, 2013 Sales Revenue, Services, Net Customer Concentration Risk CenturyLink	Jan. 25, 2014 Sales Revenue, Services, Net Customer Concentration Risk CenturyLink	Jan. 26, 2013 Sales Revenue, Services, Net Customer Concentration Risk CenturyLink	Jan. 25, 2014 Sales Revenue, Services, Net Customer Concentration Risk Comcast	Jan. 26, 2013 Sales Revenue, Services, Net Customer Concentration Risk Comcast	Jan. 25, 2014 Sales Revenue, Services, Net Customer Concentration Risk Comcast	Jan. 26, 2013 Sales Revenue, Services, Net Customer Concentration Risk Comcast	Jan. 25, 2014 Trade Accounts Receivable and Costs and Estimated Earnings Customer Concentration Risk AT&T	Jan. 26, 2013 Trade Accounts Receivable and Costs and Estimated Earnings Customer Concentration Risk AT&T	Jul. 27, 2013 Trade Accounts Receivable and Costs and Estimated Earnings Customer Concentration Risk AT&T	Jan. 25, 2014 Trade Accounts Receivable and Costs and Estimated Earnings Customer Concentration Risk CenturyLink	Jan. 26, 2013 Trade Accounts Receivable and Costs and Estimated Earnings Customer Concentration Risk CenturyLink	Jul. 27, 2013 Trade Accounts Receivable and Costs and Estimated Earnings Customer Concentration Risk CenturyLink	Jan. 25, 2014 Trade Accounts Receivable and Costs and Estimated Earnings Customer Concentration Risk Windstream Corporation	Jan. 26, 2013 Trade Accounts Receivable and Costs and Estimated Earnings Customer Concentration Risk Windstream Corporation	Jul. 27, 2013 Trade Accounts Receivable and Costs and Estimated Earnings Customer Concentration Risk Windstream Corporation
Concentration Risk [Line Items]
Number of customers classified as highly concentrated	5
Concentration risk percentage		58.20%	18.70%	13.60%	18.00%	13.50%	14.40%	14.70%	15.00%	14.20%	12.00%	11.00%	11.20%	11.80%	14.70%	12.60%		12.00%	13.70%		7.50%	13.00%
Accounts receivable, costs, and estimated earnings in excess of billings															$ 59.7		$ 57.4	$ 48.8		$ 62.6	$ 30.6		$ 59.4