Net Loss Per Share Attributable to Common Stockholders - Antidilutive (Details) - shares shares in Thousands	6 Months Ended
	Jul. 31, 2020	Jul. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from diluted net loss per share (in shares)	20,064	29,966
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)	728	1,316
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)	8,311	5,729
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)	9,871	21,267
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)	1,154	1,654