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Concentration of Credit Risk - Customer Type (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Oct. 27, 2018 | Oct. 28, 2017 | Oct. 27, 2018 | Oct. 28, 2017
Concentration Risk |  |  |  |
Contract revenues | $ 848,237 | $ 756,215 | $ 2,379,081 | $ 2,322,741
Concentration risk percentage | 100.00% | 100.00% | 100.00% | 100.00%
Customer Concentration Risk | Sales Revenue, Services, Net |  |  |  |
Concentration Risk |  |  |  |
Concentration risk percentage |  |  | 10.00% |
Customer Concentration Risk | Sales Revenue, Services, Net | Telecommunications |  |  |  |
Concentration Risk |  |  |  |
Contract revenues | $ 773,200 | $ 687,300 | $ 2,167,100 | $ 2,124,700
Concentration risk percentage | 91.10% | 90.90% | 91.10% | 91.50%
Customer Concentration Risk | Sales Revenue, Services, Net | Underground facility locating |  |  |  |
Concentration Risk |  |  |  |
Contract revenues | $ 48,800 | $ 48,400 | $ 142,900 | $ 138,000
Concentration risk percentage | 5.80% | 6.40% | 6.00% | 5.90%
Customer Concentration Risk | Sales Revenue, Services, Net | Electrical and gas utilities and other |  |  |  |
Concentration Risk |  |  |  |
Contract revenues | $ 26,200 | $ 20,500 | $ 69,100 | $ 60,000
Concentration risk percentage | 3.10% | 2.70% | 2.90% | 2.60%
Five Unnamed Customers | Customer Concentration Risk | Sales Revenue, Services, Net |  |  |  |
Concentration Risk |  |  |  |
Concentration risk percentage |  |  | 78.30% | 76.70%

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