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Concentration of Credit Risk (Details) $ in Millions	3 Months Ended
	Oct. 24, 2015 USD ($) customer	Jul. 25, 2015 USD ($)	Oct. 25, 2014
Concentration Risk [Line Items]
Number of customers classified as highly concentrated | customer	5
Sales Revenue, Services, Net | Customer Concentration Risk | Five Unnamed Customers
Concentration Risk [Line Items]
Concentration risk percentage	64.90%		59.40%
Sales Revenue, Services, Net | Customer Concentration Risk | AT&T Inc.
Concentration Risk [Line Items]
Concentration risk percentage	19.10%		21.20%
Sales Revenue, Services, Net | Customer Concentration Risk | CenturyLink, Inc.
Concentration Risk [Line Items]
Concentration risk percentage	15.60%		13.10%
Sales Revenue, Services, Net | Customer Concentration Risk | Comcast Corporation
Concentration Risk [Line Items]
Concentration risk percentage	12.00%		12.80%
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | AT&T Inc.
Concentration Risk [Line Items]
Concentration risk percentage	16.90%	17.70%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 115.8	$ 101.7
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | CenturyLink, Inc.
Concentration Risk [Line Items]
Concentration risk percentage	14.70%	14.00%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 100.8	$ 80.1
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Comcast Corporation
Concentration Risk [Line Items]
Concentration risk percentage	10.30%	11.00%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 70.6	$ 63.0
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Windstream Corporation [Member]
Concentration Risk [Line Items]
Concentration risk percentage	10.50%	8.30%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 71.8	$ 47.8
Trade Accounts Receivable and Costs and Estimated Earnings | Customer Concentration Risk | Another Customer
Concentration Risk [Line Items]
Concentration risk percentage	13.10%	11.20%
Accounts receivable, costs, and estimated earnings in excess of billings	$ 89.9	$ 64.5

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. This also includes the amount included in cost of uncompleted contracts in excess of related billings, or unbilled accounts receivable.

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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=6927468&loc=d3e6351-108592



Reference 2: http://www.xbrl.org/2003/role/presentationRef



-Publisher FASB



-Name Accounting Standards Codification



-Topic 825



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-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13531-108611



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-Name Accounting Standards Codification



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