Equity Incentive Plans - Early Exercise of Stock Options (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016	Jan. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock (in shares)			1,242,172
Common stock subject to repurchase (in shares)	311,710		311,710		118,059
Fair value of shares subject to repurchase	$ 2.4		$ 2.4		$ 0.8
Early Exercised Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock (in shares)	99,618	21,506	358,380	202,973
Stock repurchased (in shares)	11,362	3,437	21,721	3,516