Concentration of Credit Risk - Revenue Concentration Risk (Details) - USD ($) $ in Thousands	3 Months Ended
	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%