Net Loss Per Share Attributable to Common Stockholders - Summary of Potential Absolute Shares Excluded from Computation of Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - shares	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share	12,969,701	15,479,245
Convertible preferred stock (on an if-converted basis)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share	0	10,610,966
Stock Options and RSUs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share	11,072,139	4,753,796
Early Exercised Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share	0	49,233
Convertible Preferred Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share	0	40,250
Common Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share	1,897,562	25,000