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Concentration of Credit Risk (Details) $ in Millions | 3 Months Ended
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Oct. 29, 2016 USD ($) customer | Jul. 30, 2016 USD ($) | Oct. 24, 2015
Concentration Risk [Line Items] |  |  |
Number of customers classified as highly concentrated | customer | 5 |  |
Sales Revenue, Services, Net | Customer Concentration Risk |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 10.00% |  |
Sales Revenue, Services, Net | Customer Concentration Risk | Five Unnamed Customers |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 74.90% |  | 64.90%
Sales Revenue, Services, Net | Customer Concentration Risk | AT&T Inc. |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 29.00% |  | 19.10%
Sales Revenue, Services, Net | Customer Concentration Risk | Comcast |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 15.70% |  | 15.60%
Sales Revenue, Services, Net | Customer Concentration Risk | CenturyLink |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 15.10% |  | 12.00%
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 10.00% |  |
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | AT&T Inc. |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 22.90% | 20.30% |
Accounts receivable, costs, and estimated earnings in excess of billings | $ 183.5 | $ 138.8 |
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Windstream Corporation |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 11.40% | 11.50% |
Accounts receivable, costs, and estimated earnings in excess of billings | $ 90.9 | $ 79.0 |
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Another Customer |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 9.00% | 10.40% |
Accounts receivable, costs, and estimated earnings in excess of billings | $ 72.1 | $ 71.5 |
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Verizon |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 10.00% | 10.10% |
Accounts receivable, costs, and estimated earnings in excess of billings | $ 80.1 | $ 69.0 |
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Comcast |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 14.60% | 13.90% |
Accounts receivable, costs, and estimated earnings in excess of billings | $ 117.0 | $ 95.3 |
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | CenturyLink |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 13.50% | 11.50% |
Accounts receivable, costs, and estimated earnings in excess of billings | $ 108.3 | $ 79.0 |

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- Definition Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection. This also includes the amount included in cost of uncompleted contracts in excess of related billings, or unbilled accounts receivable. + References No definition available. + Details
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