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Debt - Convertible Senior Notes Due 2021 (Details)			3 Months Ended				12 Months Ended
	Sep. 15, 2015 USD ($) $ / shares shares	Sep. 09, 2015 USD ($) shares	Jul. 29, 2017 USD ($)	Apr. 29, 2017 shares	Jan. 28, 2017 shares	Oct. 24, 2015 trading_day	Jul. 29, 2017 USD ($) shares	Jul. 30, 2016 USD ($) shares	Jul. 25, 2015 USD ($) shares	Jul. 15, 2015 USD ($)
Debt Instrument [Line Items]
Stock repurchased and retired during period, value	$ 60,000,000	$ 60,000,000					$ 62,909,000	$ 169,997,000	$ 87,146,000
Stock repurchased and retired during period, shares | shares	805,000	805,000		400,000	313,006		713,006	2,511,578	1,669,924
Purchase of convertible note hedges							$ 0	$ 115,818,000	$ 0
Amortization of debt issuance costs and other							17,610,000	14,709,000	$ 0
0.75% Convertible Senior Notes Due 2021
Debt Instrument [Line Items]
Debt instrument, face amount	$ 485,000,000		$ 485,000,000				$ 485,000,000	485,000,000
Debt, interest rate (in percent)			0.75%				0.75%
Proceeds from convertible debt	471,700,000
Purchase of convertible note hedges	41,100,000
Proceeds from the issuance of debt for corporate purposes	$ 73,900,000
Debt instrument conversion ratio	0.0103211
Debt instrument, convertible, conversion price (per share) | $ / shares	$ 96.89
Convertible debt, trading day threshold | trading_day						20
Convertible debt, consecutive trading day threshold						30 days
Convertible debt, percentage of stock trigger price threshold						130.00%
Convertible debt, measurement period for consecutive periods threshold						5 days
Convertible debt, measurement for consecutive periods threshold						5 days
Convertible debt, measurement period for percentage of product sale price of common stock and applicable conversion threshold						98.00%
Convertible debt, comparable yield			5.50%
Amortization of debt issuance costs and other							$ 17,600,000	14,700,000
Long-termdebt, fair value			$ 474,500,000				474,500,000	458,700,000
Convertible Debt			392,233,000				392,233,000	373,077,000
Unamortized discount			84,069,000				84,069,000	101,679,000
Debt issuance cost	$ 15,100,000		$ 8,698,000				$ 8,698,000	$ 10,244,000
7.125% Senior Subordinated Notes Due 2021
Debt Instrument [Line Items]
Debt instrument, face amount										$ 277,500,000.0
Debt, interest rate (in percent)			7.125%			7.125%	7.125%			7.125%
Repayments of debt	$ 296,600,000

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