Concentration of Credit Risk - Trade Receivable Risk (Details) - USD ($) $ in Thousands	3 Months Ended
	Oct. 28, 2017	Jul. 29, 2017
Concentration Risk [Line Items]
Accounts receivable, net	$ 347,727	$ 369,800
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings
Concentration Risk [Line Items]
Concentration risk percentage	10.00%
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings | Comcast Corporation
Concentration Risk [Line Items]
Accounts receivable, net	$ 170,800	$ 159,700
Concentration risk percentage	22.90%	21.30%
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings | CenturyLink, Inc.
Concentration Risk [Line Items]
Accounts receivable, net	$ 130,100	$ 136,100
Concentration risk percentage	17.40%	18.10%
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings | AT&T Inc.
Concentration Risk [Line Items]
Accounts receivable, net	$ 83,700	$ 87,100
Concentration risk percentage	11.20%	11.60%
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings | Windstream Corporation
Concentration Risk [Line Items]
Accounts receivable, net	$ 72,000	$ 84,700
Concentration risk percentage	9.60%	11.30%
Customer Concentration Risk | Trade Accounts Receivable and Costs and Estimated Earnings | Verizon Communications Inc
Concentration Risk [Line Items]
Accounts receivable, net	$ 84,300	$ 73,700
Concentration risk percentage	11.30%	9.80%