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Debt - Convertible Note Hedge and Warrant Transactions (Details) - USD ($) $ / shares in Units, shares in Thousands		6 Months Ended	12 Months Ended
	Sep. 15, 2015	Jan. 27, 2018	Jan. 25, 2020	Jan. 26, 2019	Jul. 29, 2017
Debt Instrument [Line Items]
Proceeds from borrowings on senior credit agreement, including term loans		$ 0	$ 475,000,000	$ 423,188,000	$ 707,000,000
Convertible Note Hedge
Debt Instrument [Line Items]
Debt instrument, convertible, conversion price (per share)	$ 96.89		$ 96.89	$ 96.89
Payment for financing derivatives	$ 115,800,000
Proceeds from borrowings on senior credit agreement, including term loans			$ 25,000,000
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (shares)	4,748
Deferred tax liability	$ 43,400,000
Deferred tax asset, derivative instrument	43,200,000
0.75% Convertible Senior Notes Due 2021
Debt Instrument [Line Items]
Debt instrument, face amount	$ 485,000,000.0		$ 460,000,000.0	$ 485,000,000
Debt instrument, convertible, conversion price (per share)	$ 96.89
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (shares)			4,748	5,006
Class of warrant or right, exercise price of warrants or rights (per warrant)			$ 130.43
Warrant Transaction
Debt Instrument [Line Items]
Proceeds from borrowings on senior credit agreement, including term loans			$ 25,000,000
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (shares)	4,748			5,006
Class of warrant or right, exercise price of warrants or rights (per warrant)	$ 130.43