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Concentration of Credit Risk - Revenue Concentration Risk (Details) - Sales Revenue, Services, Net - Customer Concentration Risk	12 Months Ended
	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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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
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-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
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-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13537-108611

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