Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net loss attributable to common stockholders	$ (51,889)	$ (32,877)	$ (77,866)	$ (66,494)
Weighted-average shares used in computing net loss per share attributable to Class A and Class B common stockholders, basic and diluted	130,091	44,105	89,335	43,864
Net loss per share attributable to Class A and Class B common stockholders, basic and diluted	$ (0.40)	$ (0.75)	$ (0.87)	$ (1.52)
Class A common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net loss attributable to common stockholders	$ (4,308)		$ (4,784)
Weighted-average shares used in computing net loss per share attributable to Class A and Class B common stockholders, basic and diluted	10,800		5,489
Net loss per share attributable to Class A and Class B common stockholders, basic and diluted	$ (0.40)		$ (0.87)
Class B common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net loss attributable to common stockholders	$ (47,581)		$ (73,082)
Weighted-average shares used in computing net loss per share attributable to Class A and Class B common stockholders, basic and diluted	119,291		83,846
Net loss per share attributable to Class A and Class B common stockholders, basic and diluted	$ (0.40)		$ (0.87)