Concentration of Credit Risk (Details) (Customer Concentration Risk, USD $) In Millions, unless otherwise specified	3 Months Ended		0 Months Ended						3 Months Ended
	Oct. 27, 2012 Five Unnamed Customers [Member]	Oct. 29, 2011 Five Unnamed Customers [Member]	Oct. 27, 2012 Trade Accountss Receivable and Costs and Estimated Earnings [Member] CenturyLink	Jul. 28, 2012 Trade Accountss Receivable and Costs and Estimated Earnings [Member] CenturyLink	Oct. 27, 2012 Trade Accountss Receivable and Costs and Estimated Earnings [Member] AT&T	Jul. 28, 2012 Trade Accountss Receivable and Costs and Estimated Earnings [Member] AT&T	Oct. 27, 2012 Trade Accountss Receivable and Costs and Estimated Earnings [Member] Windstream Corporation	Jul. 28, 2012 Trade Accountss Receivable and Costs and Estimated Earnings [Member] Windstream Corporation	Oct. 27, 2012 Sales Revenue, Services, Net CenturyLink	Oct. 29, 2011 Sales Revenue, Services, Net CenturyLink	Oct. 27, 2012 Sales Revenue, Services, Net AT&T	Oct. 29, 2011 Sales Revenue, Services, Net AT&T	Oct. 27, 2012 Sales Revenue, Services, Net Comcast	Oct. 29, 2011 Sales Revenue, Services, Net Comcast	Oct. 27, 2012 Sales Revenue, Services, Net Verizon	Oct. 29, 2011 Sales Revenue, Services, Net Verizon
Concentration Risk [Line Items]
Concentration Risk, Percentage	59.60%	59.90%	16.30%	17.70%	9.70%	9.20%	12.90%	13.20%	13.70%	13.30%	13.50%	15.20%	12.70%	12.90%	10.20%	12.00%
Accounts receivable, costs, and estimated earnings in excess of billings			$ 44.3	$ 47.6	$ 26.4	$ 24.7	$ 35.1	$ 35.4