Equity Incentive Plans - Early Exercise of Stock Options (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock (in shares)	1,263,722	1,534,211
Common stock subject to repurchase (in shares)	256,640	118,059
Fair value of shares subject to repurchase	$ 2.0	$ 0.8
Early Exercised Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock (in shares)	363,894	240,678
Stock repurchased (in shares)	34,710	6,354