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		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Earnings Per Share [Abstract]
Net loss	$ (61,701)	$ (59,550)	$ (124,075)	$ (123,338)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)	209,193	192,730	207,515	191,026
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.29)	$ (0.31)	$ (0.60)	$ (0.65)