Net Loss per Share Attributable to Common Stockholders - Net Loss per Share (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
Earnings Per Share [Abstract]
Net loss	$ (66,018)	$ (60,123)	$ (166,354)	$ (124,427)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)	251,298	229,359	248,366	226,609
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.26)	$ (0.26)	$ (0.67)	$ (0.55)