Concentration of Credit Risk (Details) (USD $) In Millions, unless otherwise specified		3 Months Ended		0 Months Ended						3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jan. 26, 2013 Customers	Jan. 26, 2013 Customer Concentration Risk Five Unnamed Customers [Member]	Jan. 28, 2012 Customer Concentration Risk Five Unnamed Customers [Member]	Jan. 26, 2013 Trade Accountss Receivable and Costs and Estimated Earnings [Member] Customer Concentration Risk CenturyLink	Jul. 28, 2012 Trade Accountss Receivable and Costs and Estimated Earnings [Member] Customer Concentration Risk CenturyLink	Jan. 26, 2013 Trade Accountss Receivable and Costs and Estimated Earnings [Member] Customer Concentration Risk Windstream Corporation	Jul. 28, 2012 Trade Accountss Receivable and Costs and Estimated Earnings [Member] Customer Concentration Risk Windstream Corporation	Jan. 26, 2013 Trade Accountss Receivable and Costs and Estimated Earnings [Member] Customer Concentration Risk Verizon [Member]	Jul. 28, 2012 Trade Accountss Receivable and Costs and Estimated Earnings [Member] Customer Concentration Risk Verizon [Member]	Jan. 26, 2013 Sales Revenue, Services, Net Customer Concentration Risk CenturyLink	Jan. 28, 2012 Sales Revenue, Services, Net Customer Concentration Risk CenturyLink	Jan. 26, 2013 Sales Revenue, Services, Net Customer Concentration Risk CenturyLink	Jan. 28, 2012 Sales Revenue, Services, Net Customer Concentration Risk CenturyLink	Jan. 26, 2013 Sales Revenue, Services, Net Customer Concentration Risk AT&T	Jan. 28, 2012 Sales Revenue, Services, Net Customer Concentration Risk AT&T	Jan. 26, 2013 Sales Revenue, Services, Net Customer Concentration Risk AT&T	Jan. 28, 2012 Sales Revenue, Services, Net Customer Concentration Risk AT&T	Jan. 26, 2013 Sales Revenue, Services, Net Customer Concentration Risk Comcast	Jan. 28, 2012 Sales Revenue, Services, Net Customer Concentration Risk Comcast	Jan. 26, 2013 Sales Revenue, Services, Net Customer Concentration Risk Comcast	Jan. 28, 2012 Sales Revenue, Services, Net Customer Concentration Risk Comcast	Jan. 26, 2013 Sales Revenue, Services, Net Customer Concentration Risk Verizon [Member]	Jan. 28, 2012 Sales Revenue, Services, Net Customer Concentration Risk Verizon [Member]	Jan. 26, 2013 Sales Revenue, Services, Net Customer Concentration Risk Verizon [Member]	Jan. 28, 2012 Sales Revenue, Services, Net Customer Concentration Risk Verizon [Member]
Concentration Risk [Line Items]
Number of customers classified as highly concentrated	5
Concentration Risk, Percentage		58.20%	59.10%	12.80%	17.70%	14.30%	13.20%	7.10%	11.30%	14.70%	14.50%	14.20%	13.90%	13.60%	13.50%	13.50%	14.40%	11.00%	12.50%	11.80%	12.70%	9.10%	9.90%	9.60%	11.00%
Accounts receivable, costs, and estimated earnings in excess of billings				$ 48.1	$ 47.6	$ 54.0	$ 35.4	$ 26.6	$ 30.5