Concentration of Credit Risk - Revenue Concentration Risk (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%
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			78.30%	76.70%
Sales Revenue, Services, Net | Customer Concentration Risk | Verizon Communications Inc.
Concentration Risk
Contract revenues	$ 164,600	$ 143,500	$ 506,800	$ 520,100
Concentration risk percentage	19.40%	19.00%	21.30%	22.40%
Sales Revenue, Services, Net | Customer Concentration Risk | Comcast Corporation
Concentration Risk
Contract revenues	$ 176,300	$ 165,000	$ 506,700	$ 471,000
Concentration risk percentage	20.80%	21.80%	21.30%	20.30%
Sales Revenue, Services, Net | Customer Concentration Risk | AT&T Inc.
Concentration Risk
Contract revenues	$ 174,100	$ 80,600	$ 443,500	$ 225,700
Concentration risk percentage	20.50%	10.70%	18.60%	9.70%
Sales Revenue, Services, Net | Customer Concentration Risk | CenturyLink, Inc.(1)
Concentration Risk
Contract revenues	$ 118,800	$ 146,100	$ 316,000	$ 457,600
Concentration risk percentage	14.00%	19.30%	13.30%	19.70%
Sales Revenue, Services, Net | Customer Concentration Risk | Total other customers combined
Concentration Risk
Contract revenues	$ 214,400	$ 221,000	$ 606,100	$ 648,300
Concentration risk percentage	25.30%	29.20%	25.50%	27.90%