Equity Incentive Plans - Early Exercise of Stock Options (Details) - USD ($)	12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of common stock upon exercise of stock options (in shares)	9,397,220
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
Repurchase of Common Stock (in shares)	0	0
Common stock subject to repurchase (in shares)	85,262
Common stock subject to repurchase, aggregate price		$ 319,629.60