Debt - Components of the Convertible Notes (Details) - USD ($)		6 Months Ended	12 Months Ended
	Sep. 15, 2015	Jan. 27, 2018	Jul. 29, 2017	Jul. 30, 2016	Jul. 25, 2015
Debt Instrument [Line Items]
Proceeds from sale of warrants		$ 0	$ 0	$ 74,690,000	$ 0
Payments for Hedge, Financing Activities		0	0	115,818,000	0
Equity component of 0.75% senior convertible notes due 2021, net		112,600,000
Amortization of debt discount		9,170,000	17,610,000	14,709,000	$ 0
Reported Value Measurement
Debt Instrument [Line Items]
Net carrying amount of Notes		402,249,000	392,233,000	373,077,000
Estimate of Fair Value Measurement
Debt Instrument [Line Items]
Debt instrument, face amount		659,649,000	567,256,000	570,603,000
Less: Debt discount and debt issuance costs		(82,751,000)	(92,767,000)	(111,923,000)
Net carrying amount of Notes		576,898,000	474,489,000	458,680,000
0.75% Convertible Senior Notes Due 2021
Debt Instrument [Line Items]
Proceeds from sale of warrants	$ 74,700,000
Payments for Hedge, Financing Activities	41,100,000
Debt instrument, face amount	485,000,000.0	485,000,000	485,000,000	485,000,000
Debt Instrument, Unamortized Discount		(74,899,000)	(84,069,000)	(101,679,000)
Debt issuance cost		(7,852,000)	(8,698,000)	(10,244,000)
Net carrying amount of Notes		402,249,000	392,233,000	373,077,000
Amortization of debt discount		$ 9,200,000	$ 17,600,000	$ 14,700,000
Convertible Note Hedge
Debt Instrument [Line Items]
Payments for Hedge, Financing Activities	$ 115,800,000