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Debt - Components of the Convertible Notes (Details) - USD ($)	3 Months Ended		9 Months Ended
	Oct. 27, 2018	Oct. 28, 2017	Oct. 27, 2018	Oct. 28, 2017	Jan. 27, 2018	Sep. 15, 2015
Debt Instrument [Line Items]
Equity component of 0.75% senior convertible notes due 2021, net	$ 112,600,000		$ 112,600,000
Amortization of debt discount			14,223,000	$ 13,471,000
Estimate of Fair Value Measurement
Debt Instrument [Line Items]
Debt instrument, face amount	492,275,000		492,275,000		$ 659,649,000
Less: Debt discount and debt issuance costs	(67,165,000)		(67,165,000)		(82,751,000)
Net carrying amount of Notes	425,110,000		425,110,000		576,898,000
0.75% Convertible Senior Notes Due 2021
Debt Instrument [Line Items]
Debt instrument, face amount	485,000,000		485,000,000		485,000,000	$ 485,000,000.0
Debt Instrument, Unamortized Discount	(60,676,000)		(60,676,000)		(74,899,000)
Debt issuance cost	(6,489,000)		(6,489,000)		(7,852,000)
Net carrying amount of Notes	417,835,000		417,835,000		$ 402,249,000
Amortization of debt discount	$ 4,800,000	$ 4,500,000	$ 14,200,000	$ 13,500,000