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Concentration of Credit Risk - Narratives (Details) $ in Thousands | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Jan. 26, 2019 USD ($) customer | Oct. 27, 2018 USD ($) | Jul. 28, 2018 USD ($) | Apr. 28, 2018 USD ($) | Jan. 27, 2018 USD ($) | Oct. 28, 2017 USD ($) | Jul. 29, 2017 USD ($) | Apr. 29, 2017 USD ($) | Jan. 28, 2017 USD ($) | Oct. 29, 2016 USD ($) | Jan. 27, 2018 USD ($) | Jan. 28, 2017 USD ($) | Jan. 26, 2019 USD ($) customer | Jul. 29, 2017 USD ($) | Jul. 30, 2016 USD ($) | Jan. 28, 2018 USD ($)
Concentration Risk [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues | $ 748,619 | $ 848,237 | $ 799,470 | $ 731,375 | $ 655,133 | $ 756,215 | $ 780,188 | $ 786,338 | $ 701,131 | $ 799,223 | $ 1,411,348 | $ 1,500,355 | $ 3,127,700 | $ 3,066,880 | $ 2,672,542 |
Number of customers classified as highly concentrated | customer | 5 |  |  |  |  |  |  |  |  |  |  |  | 5 |  |  |
Concentration risk percentage |  |  |  |  |  |  |  |  |  |  | 100.00% |  | 100.00% | 100.00% | 100.00% |
Accounts receivable, net | $ 625,258 |  |  |  | 318,684 |  |  |  |  |  | $ 318,684 |  | $ 625,258 |  |  | $ 630,400
Sales Revenue, Services, Net | Customer Concentration Risk |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Concentration risk percentage |  |  |  |  |  |  |  |  |  |  |  |  | 10.00% |  |  |
Sales Revenue, Services, Net | Customer Concentration Risk | ATT [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  |  | $ 290,100 |  | $ 664,200 | $ 806,700 | $ 650,900 |
Concentration risk percentage |  |  |  |  |  |  |  |  |  |  | 20.60% |  | 21.20% | 26.30% | 24.40% |
Sales Revenue, Services, Net | Customer Concentration Risk | Five Unnamed Customers |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Concentration risk percentage |  |  |  |  |  |  |  |  |  |  | 75.80% |  | 78.40% | 76.80% | 70.10% |
Trade Accounts Receivable and Costs and Estimated Earnings [Member] | Customer Concentration Risk | ATT [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Concentration risk percentage |  |  |  |  |  |  |  |  |  |  | 11.60% |  | 11.00% |  |  |
Accounts receivable, net | $ 90,600 |  |  |  | $ 79,200 |  |  |  |  |  | $ 79,200 |  | $ 90,600 |  |  |

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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. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130549-203045 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -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 + Details
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