CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balances at Jan. 31, 2013	$ 237,544	$ 101	$ 328,277	$ (135)	$ (90,699)
Balances (in shares) at Jan. 31, 2013		100,920,350
Increase (Decrease) in Stockholders' Equity
Stock-based compensation	69,368		69,368
Issuance of common stock upon exercise of options	23,731	$ 7	23,724
Issuance of common stock upon exercise of options (in shares)		7,254,049
Issuance of common stock upon follow-on offering	539,339	$ 7	539,332
Issuance of common stock upon follow-on offering (in shares)		6,900,000
Vesting of early exercised options	112		112
Vesting of restricted stock units (in shares)		475,111
Taxes withholding related to net share settlement of equity awards	(18,156)		(18,156)
Issuance of common stock upon ESPP purchase	11,434	$ 1	11,433
Issuance of common stock upon ESPP purchase (in shares)		550,006
Excess tax benefits from employee stock plans	351		351
Net change in cumulative translation adjustment	193			193
Net loss	(79,008)				(79,008)
Balances at Jan. 31, 2014	784,908	$ 116	954,441	58	(169,707)
Balances (in shares) at Jan. 31, 2014		116,099,516
Increase (Decrease) in Stockholders' Equity
Stock-based compensation	214,179		214,179
Issuance of common stock upon exercise of options	$ 16,792	$ 4	16,788
Issuance of common stock upon exercise of options (in shares)	0	4,213,746
Vesting of early exercised options	$ 112		112
Vesting of restricted stock units (in shares)		2,862,027
Vesting of restricted stock units		$ 3	(3)
Issuance of common stock upon ESPP purchase	14,494	$ 0	14,494
Issuance of common stock upon ESPP purchase (in shares)		363,203
Excess tax benefits from employee stock plans	847		847
Unrealized Gain (Loss) from Investments	2			2
Net change in cumulative translation adjustment	(897)			(897)
Net loss	(217,116)				(217,116)
Balances at Jan. 31, 2015	813,321	$ 123	1,200,858	(837)	(386,823)
Balances (in shares) at Jan. 31, 2015		123,538,492
Increase (Decrease) in Stockholders' Equity
Stock-based compensation	292,257		292,257
Issuance of common stock upon exercise of options	$ 15,269	$ 3	15,266
Issuance of common stock upon exercise of options (in shares)	0	2,755,556
Vesting of early exercised options	$ 55		55
Vesting of restricted stock units (in shares)		4,136,073
Vesting of restricted stock units		$ 5	(5)
Issuance of restricted stock awards		671,782
Issuance of common stock upon ESPP purchase	19,342	$ 0	19,342
Issuance of common stock upon ESPP purchase (in shares)		441,564
Issuance of restricted stock awards	1	$ 1
Excess tax benefits from employee stock plans	874		874
Unrealized Gain (Loss) from Investments	(66)			(66)
Net change in cumulative translation adjustment	(2,867)			(2,867)
Net loss	(278,772)				(278,772)
Balances at Jan. 31, 2016	$ 859,414	$ 132	$ 1,528,647	$ (3,770)	$ (665,595)
Balances (in shares) at Jan. 31, 2016		131,543,467