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	3 Months Ended		9 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Earnings Per Share [Abstract]
Net loss	$ (41,649)	$ (78,813)	$ (165,724)	$ (202,151)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)	213,274	195,807	209,456	192,637
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.20)	$ (0.40)	$ (0.79)	$ (1.05)