Net Loss Per Share - Schedule of the Calculation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Numerator:
Net loss	$ (64,287)	$ (82,122)	$ (87,043)	$ (103,130)	$ (85,521)	$ (25,857)	$ (28,949)	$ (52,322)	$ (336,582)	$ (192,649)	$ (369,672)
Denominator:
Weighted-average shares used in computing net loss per share, basic and diluted (in shares)									280,772	159,816	114,141
Net loss per share, basic and diluted (in dollars per share)	$ (0.22)	$ (0.29)	$ (0.31)	$ (0.38)	$ (0.45)	$ (0.17)	$ (0.19)	$ (0.36)	$ (1.20)	$ (1.21)	$ (3.24)