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, shares in Thousands, $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Earnings Per Share [Abstract]
Net loss	$ (177,602)	$ (245,066)	$ (213,752)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)	211,609	194,714	82,460
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.84)	$ (1.26)	$ (2.59)