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Customer Concentration and Revenue Information - Trade Receivable Risk (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jan. 25, 2020 | Oct. 26, 2019 | Jul. 27, 2019 | Apr. 27, 2019 | Jan. 26, 2019 | Oct. 27, 2018 | Jul. 28, 2018 | Apr. 28, 2018 | Jan. 27, 2018 | Jan. 28, 2017 | Jan. 25, 2020 | Jan. 26, 2019 | Jul. 29, 2017
Concentration Risk [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues | $ 737,603 | $ 884,115 | $ 884,221 | $ 833,743 | $ 748,619 | $ 848,237 | $ 799,470 | $ 731,375 | $ 1,411,348 | $ 1,500,355 | $ 3,339,682 | $ 3,127,700 | $ 3,066,880
Concentration risk percentage |  |  |  |  |  |  |  |  | 100.00% |  | 100.00% | 100.00% | 100.00%
Customer Concentration Risk | Sales Revenue, Services, Net |  |  |  |  |  |  |  |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Concentration risk percentage |  |  |  |  |  |  |  |  |  |  | 10.00% |  |
Telecommunications | Customer Concentration Risk | Sales Revenue, Services, Net |  |  |  |  |  |  |  |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | $ 1,284,100 |  | $ 3,031,900 | $ 2,855,800 | $ 2,819,900
Concentration risk percentage |  |  |  |  |  |  |  |  | 91.00% |  | 90.80% | 91.30% | 91.90%
Underground facility locating | Customer Concentration Risk | Sales Revenue, Services, Net |  |  |  |  |  |  |  |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | $ 88,600 |  | $ 204,500 | $ 182,700 | $ 167,900
Concentration risk percentage |  |  |  |  |  |  |  |  | 6.30% |  | 6.10% | 5.80% | 5.50%
Electrical and gas utilities and other | Customer Concentration Risk | Sales Revenue, Services, Net |  |  |  |  |  |  |  |  |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | $ 38,600 |  | $ 103,300 | $ 89,200 | $ 79,100
Concentration risk percentage |  |  |  |  |  |  |  |  | 2.70% |  | 3.10% | 2.90% | 2.60%

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