Net Loss Per Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares shares in Thousands	12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive shares	13,431	81,972	75,334
Total all series
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive shares	0	68,480	62,145
Shares subject to outstanding common stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive shares	13,297	13,355	13,052
Shares issuable pursuant to the Employee Stock Purchase Plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive shares	134	0	0
Total all series | Convertible preferred stock warrant
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive shares	0	137	137