Equity Incentive Plans - Schedule of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Shares Available for Grant
Balance - beginning of period (in shares)	678,260	974,433
Authorized (in shares)	6,979,900	3,000,000
Options granted (in shares)	(3,642,275)	(4,404,228)
Early exercised shares repurchased (in shares)	34,710	6,354
Options forfeited and expired (in shares)	(831,715)	(1,101,701)
Balance - end of period (in shares)	4,636,564	678,260	974,433
Shares
Balance - beginning of period (in shares)	11,090,597	9,322,281
Options granted (in shares)	(3,642,275)	(4,404,228)
Options exercised (in shares)	(1,263,722)	(1,534,211)
Options forfeited and expired (in shares)	(831,715)	(1,101,701)
Balance - end of period (in shares)	12,637,435	11,090,597	9,322,281
Options vested and exercisable (in shares)	5,540,858	4,344,092
Options vested and exercisable - Stock options vested and expected to vest (in shares)	12,637,435
Weighted- Average Exercise Price Per Share
Balance - beginning of period (in dollars per share)	$ 6.47	$ 13.20
Options granted (in dollars per share)	10.80	6.74
Options exercised (in dollars per share)	6.59	5.43
Options forfeited and expired (in dollars per share)	7.73	11.09
Balance - end of period (in dollars per share)	7.63	6.47	$ 13.20
Options vested and exercisable (in dollars per share)	6.33	$ 6.21
Options vested and exercisable - Stock options vested and expected to vest (in dollars per share)	$ 7.63
Weighted- Average Remaining Contractual Term (In Years)
Balance	7 years 8 months 12 days	8 years 2 months 12 days	8 years 3 months 18 days
Options vested and exercisable	6 years 7 months 6 days	7 years 3 months 18 days
Stock options vested and expected to vest	7 years 8 months 12 days
Aggregate Intrinsic Value
Balance	$ 246,227	$ 21,717	$ 8,459
Options vested and exercisable	115,122	$ 9,875
Stock options vested and expected to vest, intrinsic value	$ 246,227
Restricted Stock Units (RSUs)
Shares Available for Grant
RSUs granted (in shares)	(245,746)	0