Concentration of Credit Risk - Revenue Concentration Risk (Details) - USD ($) $ in Thousands	3 Months Ended
	Apr. 25, 2020	Apr. 27, 2019
Concentration Risk
Contract revenues	$ 814,322	$ 833,743
Concentration risk percentage	100.00%	100.00%
Revenue Benchmark | Customer Concentration Risk
Concentration Risk
Concentration risk percentage	10.00%
Revenue Benchmark | Customer Concentration Risk | Five Unnamed Customers
Concentration Risk
Concentration risk percentage	78.50%	80.40%
Revenue Benchmark | Customer Concentration Risk | Verizon Communications Inc.
Concentration Risk
Contract revenues	$ 176,100	$ 179,800
Concentration risk percentage	21.60%	21.60%
Revenue Benchmark | Customer Concentration Risk | AT&T Inc.
Concentration Risk
Contract revenues	$ 154,000	$ 209,300
Concentration risk percentage	18.90%	25.10%
Revenue Benchmark | Customer Concentration Risk | CenturyLink, Inc.
Concentration Risk
Contract revenues	$ 148,800	$ 109,800
Concentration risk percentage	18.30%	13.20%
Revenue Benchmark | Customer Concentration Risk | Comcast Corporation
Concentration Risk
Contract revenues	$ 118,000	$ 137,100
Concentration risk percentage	14.50%	16.40%
Revenue Benchmark | Customer Concentration Risk | Total other customers combined
Concentration Risk
Contract revenues	$ 217,400	$ 197,700
Concentration risk percentage	26.70%	23.70%