Net Loss per Share - Schedule of Antidilutive Securities Excluded from the Computation of Diluted Net loss per share (Details) - shares	12 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Redeemable convertible preferred stock (as converted)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	0	19,534,014
Redeemable convertible preferred stock warrants (as converted)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	0	22,592
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	0	90,143
Stock options to purchase common stock | Class A Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	2,145,462	3,174,009	2,552,397
Stock options to purchase common stock | Class B Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	5,076,831	7,691,386	9,612,572
Unvested restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	2,914,575	1,447,642	0
Early exercised stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	29,532	126,447	236,675
Shares underlying the conversion spread in the 2024 Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	2,112,279	227,982	0