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Concentration of Credit Risk - Revenue Concentration Risk (Details) - USD ($) $ in Thousands | 3 Months Ended
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Apr. 28, 2018 | Apr. 29, 2017
Concentration Risk |  |
Contract revenues | $ 731,375 | $ 786,338
Concentration risk percentage | 100.00% | 100.00%
Sales Revenue, Services, Net | Customer Concentration Risk |  |
Concentration Risk |  |
Concentration risk percentage | 10.00% |
Sales Revenue, Services, Net | Customer Concentration Risk | Five Unnamed Customers |  |
Concentration Risk |  |
Concentration risk percentage | 78.80% | 78.40%
Sales Revenue, Services, Net | Customer Concentration Risk | AT&T Inc. |  |
Concentration Risk |  |
Contract revenues | $ 177,000 | $ 213,100
Concentration risk percentage | 24.20% | 27.10%
Sales Revenue, Services, Net | Customer Concentration Risk | Comcast Corporation |  |
Concentration Risk |  |
Contract revenues | $ 159,200 | $ 152,900
Concentration risk percentage | 21.80% | 19.40%
Sales Revenue, Services, Net | Customer Concentration Risk | Verizon Communications Inc. |  |
Concentration Risk |  |
Contract revenues | $ 122,100 | $ 66,800
Concentration risk percentage | 16.70% | 8.50%
Sales Revenue, Services, Net | Customer Concentration Risk | CenturyLink, Inc.(1) |  |
Concentration Risk |  |
Contract revenues | $ 89,700 | $ 146,200
Concentration risk percentage | 12.30% | 18.60%
Sales Revenue, Services, Net | Customer Concentration Risk | Total other customers combined |  |
Concentration Risk |  |
Contract revenues | $ 183,400 | $ 207,300
Concentration risk percentage | 25.00% | 26.40%

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