Financial Instruments - Summary of Cash Equivalents, Marketable Securities and Restricted Cash by Significant Investment Categories (Details) - USD ($) $ in Thousands	Jul. 31, 2016	Jan. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 385,953	$ 52,746
Gross Unrealized Gains	1,375	0
Gross Unrealized Losses	(24)	0
Fair Value	387,304	52,746
Cash Equivalents	22,948	45,614
Marketable Securities	364,356	0
Restricted Cash	12,732	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 Deposit \| 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	12,732
U.S. Government Treasury Notes \| Level 2
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	135,581
Gross Unrealized Gains	181
Gross Unrealized Losses	(3)
Fair Value	135,759
Cash Equivalents	18,546
Marketable Securities	117,213
Restricted Cash	0
U.S. Government Agencies \| Level 2
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	47,655
Gross Unrealized Gains	41
Gross Unrealized Losses	(6)
Fair Value	47,690
Cash Equivalents	4,001
Marketable Securities	43,689
Restricted Cash	0
Corporate Debt Securities \| Level 2
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	200,093
Gross Unrealized Gains	1,146
Gross Unrealized Losses	(15)
Fair Value	201,224
Cash Equivalents	401
Marketable Securities	200,823
Restricted Cash	0
Foreign Government Bonds \| Level 2
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,624
Gross Unrealized Gains	7
Gross Unrealized Losses	0
Fair Value	2,631
Cash Equivalents	0
Marketable Securities	2,631
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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