Net Loss Per Share Attributable to Common Stockholders - Summary of Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Earnings Per Share Diluted [Line Items]
Net loss	$ (157,659)	$ (105,801)	$ (100,968)
Net loss attributable to common stockholders	$ (137,911)	$ (105,801)	$ (100,968)
Weighted-average common shares outstanding	19,805,320	3,523,695	3,299,908
Weighted-average unvested common shares subject to repurchase	(41,636)	(81,146)	(158,961)
Weighted-average shares used in computing net loss per share attributable to common stockholders—basic and diluted	19,763,684	3,442,549	3,140,947
Net loss per share attributable to common stockholders— basic and diluted	$ (6.98)	$ (30.73)	$ (32.15)
Series E and E-1 Converible Preferred Stock
Earnings Per Share Diluted [Line Items]
Deemed dividend to Series E and E-1 Convertible Preferred Stock	$ (6,588)	$ 0	$ 0
Series E, E-1 and F Convertible Preferred Stock
Earnings Per Share Diluted [Line Items]
Impact of adjustment to Series E, E-1 and F Convertible Preferred Stock	$ 26,336	$ 0	$ 0