Concentration of Credit Risk - Revenue Concentration Risk (Details) - USD ($) $ in Thousands	3 Months Ended										6 Months Ended		12 Months Ended
	Jan. 26, 2019	Oct. 27, 2018	Jul. 28, 2018	Apr. 28, 2018	Jan. 27, 2018	Oct. 28, 2017	Jul. 29, 2017	Apr. 29, 2017	Jan. 28, 2017	Oct. 29, 2016	Jan. 27, 2018	Jan. 28, 2017	Jan. 26, 2019	Jul. 29, 2017	Jul. 30, 2016
Concentration Risk [Line Items]
Concentration risk percentage											100.00%		100.00%	100.00%	100.00%
Revenues	$ 748,619	$ 848,237	$ 799,470	$ 731,375	$ 655,133	$ 756,215	$ 780,188	$ 786,338	$ 701,131	$ 799,223	$ 1,411,348	$ 1,500,355	$ 3,127,700	$ 3,066,880	$ 2,672,542
Sales Revenue, Services, Net | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk percentage													10.00%
Sales Revenue, Services, Net | Customer Concentration Risk | AT&T Inc.
Concentration Risk [Line Items]
Concentration risk percentage											21.60%		20.80%	17.70%	13.60%
Revenues											$ 304,400		$ 650,200	$ 543,600	$ 363,100
Sales Revenue, Services, Net | Customer Concentration Risk | Comcast Corporation
Concentration Risk [Line Items]
Revenues													$ 113,600
Sales Revenue, Services, Net | Customer Concentration Risk | Verizon Communications Inc.(1)
Concentration Risk [Line Items]
Concentration risk percentage											17.50%		13.60%	18.20%	14.70%
Revenues											$ 247,000		$ 425,600	$ 556,800	$ 394,000
Sales Revenue, Services, Net | Customer Concentration Risk | Verizon Communications Inc
Concentration Risk [Line Items]
Concentration risk percentage											12.00%		19.20%	9.20%	11.20%
Revenues											$ 168,700		$ 599,800	$ 282,700	$ 298,200
Sales Revenue, Services, Net | Customer Concentration Risk | Other Customers [Member]
Concentration Risk [Line Items]
Concentration risk percentage											28.30%		25.20%	28.60%	36.10%
Revenues											$ 401,100		$ 787,900	$ 877,100	$ 966,300