Equity Incentive Plans - Early Exercise of Stock Options (Details) - USD ($)	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of common stock upon exercise of stock options (in shares)	8,814,019
Early Exercise of Stock Options | Employee Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of common stock upon exercise of stock options (in shares)	0	0	0
Unvested stock option, common stock repurchased during the period (in shares)	0	0	15,000
Common stock subject to repurchase (in shares)	85,262	494,117
Common stock subject to repurchase, aggregate price	$ 300,000.0	$ 1,400,000.0