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Concentration of Credit Risk - Revenue Concentration Risk (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 26, 2019	Oct. 27, 2018	Oct. 26, 2019	Oct. 27, 2018
Concentration Risk
Contract revenues	$ 884,115	$ 848,237	$ 2,602,079	$ 2,379,081
Concentration risk percentage	100.00%	100.00%	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			78.70%	78.30%
Sales Revenue, Services, Net | Customer Concentration Risk | CenturyLink, Inc.
Concentration Risk
Contract revenues	$ 162,900	$ 164,600	$ 555,400	$ 506,800
Concentration risk percentage	18.40%	19.40%	21.30%	21.30%
Sales Revenue, Services, Net | Customer Concentration Risk | Verizon Communications Inc.
Concentration Risk
Contract revenues	$ 131,300	$ 176,300	$ 401,600	$ 506,700
Concentration risk percentage	14.90%	20.80%	15.40%	21.30%
Sales Revenue, Services, Net | Customer Concentration Risk | AT&T Inc.
Concentration Risk
Contract revenues	$ 182,100	$ 174,100	$ 566,900	$ 443,500
Concentration risk percentage	20.60%	20.50%	21.80%	18.60%
Sales Revenue, Services, Net | Customer Concentration Risk | Comcast Corporation
Concentration Risk
Contract revenues	$ 164,100	$ 118,800	$ 412,700	$ 316,000
Concentration risk percentage	18.60%	14.00%	15.90%	13.30%
Sales Revenue, Services, Net | Customer Concentration Risk | Total other customers combined
Concentration Risk
Contract revenues	$ 243,700	$ 214,400	$ 665,500	$ 606,100
Concentration risk percentage	27.50%	25.30%	25.60%	25.50%

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