Accounts Receivable Concentration Risk (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 27, 2019	Jul. 28, 2018	Jul. 27, 2019	Jul. 28, 2018	Jan. 26, 2019
Concentration Risk
Accounts receivable, net	$ 796,908		$ 796,908		$ 625,258
Concentration risk percentage	100.00%	100.00%	100.00%	100.00%
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings | Verizon Communications Inc.
Concentration Risk
Accounts receivable, net	$ 142,900		$ 142,900		$ 127,200
Concentration risk percentage			12.50%		15.40%
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings | CenturyLink, Inc.
Concentration Risk
Accounts receivable, net	481,800		$ 481,800		$ 298,400
Concentration risk percentage			42.30%		36.20%
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings | Comcast Corporation
Concentration Risk
Accounts receivable, net	171,400		$ 171,400		$ 147,200
Concentration risk percentage			15.00%		17.90%
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings | AT&T Inc.
Concentration Risk
Accounts receivable, net	$ 112,300		$ 112,300		$ 90,600
Concentration risk percentage			9.80%		11.00%