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Concentration of Credit Risk - Revenue Concentration Risk (Details) - Sales Revenue, Services, Net - Customer Concentration Risk | 12 Months Ended
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Jul. 29, 2017 | Jul. 30, 2016 | Jul. 25, 2015
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 10.00% |  |
AT&T Inc. |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 26.30% | 24.40% | 20.80%
Comcast Corporation |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 17.70% | 13.60% | 12.90%
CenturyLink, Inc. |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 17.50% | 14.50% | 14.20%
Verizon Communications Inc |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk percentage | 9.20% | 11.20% | 7.70%

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