Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net loss attributable to common stockholders	$ (35,505)	$ (42,323)	$ (113,371)	$ (108,817)
Weighted-average shares used in computing net loss per share attributable to Class A and Class B common stockholders, basic and diluted (in shares)	204,096,000	45,287,000	128,009,000	44,344,000
Net loss per share attributable to Class A and Class B common stockholders, basic and diluted (in usd per share)	$ (0.17)	$ (0.93)	$ (0.89)	$ (2.45)
Class A common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net loss attributable to common stockholders	$ (3,602)		$ (9,402)
Weighted-average shares used in computing net loss per share attributable to Class A and Class B common stockholders, basic and diluted (in shares)	20,703,000		10,616,000
Net loss per share attributable to Class A and Class B common stockholders, basic and diluted (in usd per share)	$ (0.17)		$ (0.89)
Class B common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net loss attributable to common stockholders	$ (31,903)		$ (103,969)
Weighted-average shares used in computing net loss per share attributable to Class A and Class B common stockholders, basic and diluted (in shares)	183,393,000		117,393,000
Net loss per share attributable to Class A and Class B common stockholders, basic and diluted (in usd per share)	$ (0.17)		$ (0.89)