Net Loss Per Share Attributable to Common Stockholders - Antidilutive (Details) - shares shares in Thousands	6 Months Ended
	Jul. 31, 2019	Jul. 31, 2018
Computation of diluted net loss per share attributable to common stockholders
Potential common shares excluded from diluted net loss per share	28,312	156,129
Redeemable Convertible Preferred Stock
Computation of diluted net loss per share attributable to common stockholders
Potential common shares excluded from diluted net loss per share		130,843
Redeemable convertible preferred stock warrant
Computation of diluted net loss per share attributable to common stockholders
Potential common shares excluded from diluted net loss per share		336
Shares of common stock subject to repurchase from outstanding stock options
Computation of diluted net loss per share attributable to common stockholders
Potential common shares excluded from diluted net loss per share	1,316	778
Restricted stock awards
Computation of diluted net loss per share attributable to common stockholders
Potential common shares excluded from diluted net loss per share	5,729	31
Stock options
Computation of diluted net loss per share attributable to common stockholders
Potential common shares excluded from diluted net loss per share	21,267	24,141