Accounts Receivable Concentration Credit Risk (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jan. 27, 2018	Jan. 25, 2020	Jan. 26, 2019	Jul. 29, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Net, Current		$ 817,245	$ 625,258
Concentration Risk, Percentage	100.00%	100.00%	100.00%	100.00%
Verizon Communications Inc | Trade Accounts Receivable and Costs and Estimated Earnings [Member] | Customer Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Net, Current		$ 440,200	$ 298,400
Concentration Risk, Percentage		41.80%	36.20%
Century Link, Inc | Trade Accounts Receivable and Costs and Estimated Earnings [Member] | Customer Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Net, Current		$ 175,800	$ 147,200
Concentration Risk, Percentage		16.70%	17.90%
Comcast Corporation | Trade Accounts Receivable and Costs and Estimated Earnings [Member] | Customer Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Net, Current		$ 114,000	$ 127,200
Concentration Risk, Percentage		10.80%	15.40%
AT&T Inc. | Trade Accounts Receivable and Costs and Estimated Earnings [Member] | Customer Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Net, Current		$ 97,200	$ 90,600
Concentration Risk, Percentage		9.20%	11.00%