Accounts Receivable, Contract Assets, and Contract Liabilities - Customer Credit Concentration (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 25, 2020	Jul. 27, 2019	Jul. 25, 2020	Jul. 27, 2019	Jan. 25, 2020
Concentration Risk
Amount	$ 897,833		$ 897,833		$ 817,245
% of Total	100.00%	100.00%	100.00%	100.00%
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings | Verizon Communications Inc.
Concentration Risk
Amount	$ 462,300		$ 462,300		$ 440,200
% of Total			40.70%		41.80%
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings | CenturyLink, Inc.
Concentration Risk
Amount	204,100		$ 204,100		$ 175,800
% of Total			18.00%		16.70%
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings | Comcast Corporation
Concentration Risk
Amount	$ 142,700		$ 142,700		$ 114,000
% of Total			12.60%		10.80%