Financial Instruments - Summary of Cash Equivalents, Marketable Securities and Restricted Cash by Significant Investment Categories (Details) - USD ($) $ in Thousands	Oct. 31, 2016	Jan. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 380,262	$ 52,746
Gross Unrealized Gains	664	0
Gross Unrealized Losses	(192)	0
Fair Value	380,734	52,746
Cash Equivalents	14,949	45,614
Marketable Securities	365,785	0
Restricted Cash	12,734	7,132
Money market funds \| Level 1
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		45,614
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		45,614
Cash Equivalents		45,614
Restricted Cash		0
Certificate of deposits \| Level 2
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		7,132
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		7,132
Cash Equivalents		0
Restricted Cash		$ 7,132
Money market accounts \| Level 1
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	0
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	0
Cash Equivalents	0
Marketable Securities	0
Restricted Cash	12,734
U.S. government treasury notes \| Level 2
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	143,532
Gross Unrealized Gains	67
Gross Unrealized Losses	(27)
Fair Value	143,572
Cash Equivalents	14,949
Marketable Securities	128,623
Restricted Cash	0
U.S. government agencies \| Level 2
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	41,161
Gross Unrealized Gains	13
Gross Unrealized Losses	(55)
Fair Value	41,119
Cash Equivalents	0
Marketable Securities	41,119
Restricted Cash	0
Corporate debt securities \| Level 2
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	192,944
Gross Unrealized Gains	581
Gross Unrealized Losses	(110)
Fair Value	193,415
Cash Equivalents	0
Marketable Securities	193,415
Restricted Cash	0
Foreign government bonds \| Level 2
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,625
Gross Unrealized Gains	3
Gross Unrealized Losses	0
Fair Value	2,628
Cash Equivalents	0
Marketable Securities	2,628
Restricted Cash	$ 0

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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