Net Loss Per Share Attributable to Common Stockholders - Antidilutive (Details) - shares shares in Thousands	12 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from diluted net loss per share (in shares)	23,194	158,685	143,095
Shares of common stock issuable upon conversion of redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from diluted net loss per share (in shares)	0	131,268	118,693
Shares of common stock issuable upon conversion of redeemable convertible preferred stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from diluted net loss per share (in shares)	0	336	336
Shares of common stock subject to repurchase from outstanding stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from diluted net loss per share (in shares)	984	546	872
RSUs and PSUs subject to future vesting
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from diluted net loss per share (in shares)	6,063	0	0
Shares of common stock issuable from stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from diluted net loss per share (in shares)	14,689	26,535	23,194
Share purchase rights under the employee stock purchase plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from diluted net loss per share (in shares)	1,458	0	0