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Concentration of Credit Risk - Trade Receivable Risk (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jul. 29, 2017	Jul. 29, 2017	Jul. 30, 2016
Concentration Risk [Line Items]
Accounts receivable, net	$ 369,800	$ 369,800	$ 328,030
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings
Concentration Risk [Line Items]
Concentration risk percentage	10.00%
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings | Comcast Corporation
Concentration Risk [Line Items]
Accounts receivable, net	$ 159,700	$ 159,700	$ 95,300
Concentration risk percentage		21.30%	13.90%
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings | CenturyLink, Inc.
Concentration Risk [Line Items]
Accounts receivable, net	136,100	$ 136,100	$ 79,000
Concentration risk percentage		18.10%	11.50%
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings | AT&T Inc.
Concentration Risk [Line Items]
Accounts receivable, net	87,100	$ 87,100	$ 138,800
Concentration risk percentage		11.60%	20.30%
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings | Windstream Corporation
Concentration Risk [Line Items]
Accounts receivable, net	84,700	$ 84,700	$ 79,000
Concentration risk percentage		11.30%	11.50%
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings | Verizon Communications Inc
Concentration Risk [Line Items]
Accounts receivable, net	$ 73,700	$ 73,700	$ 70,200
Concentration risk percentage		9.80%	10.20%

X

- 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Section S99
-Paragraph 1
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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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+ 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
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-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
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