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, 2018	Jul. 31, 2017	[1]	Jul. 31, 2018	Jul. 31, 2017
Earnings Per Share [Abstract]
Net loss	$ (60,123)	$ (58,411)	[2]	$ (124,427)	$ (115,570)	[3]
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)	229,359	209,193		226,609	207,515
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.26)	$ (0.28)		$ (0.55)	$ (0.56)

[1] * Prior period information has been adjusted to reflect the adoption impact of ASC 606, which we adopted on February 1, 2018.

[2] * Prior period information has been adjusted to reflect the adoption impact of ASC 606, which we adopted on February 1, 2018.

[3] * Prior period information has been adjusted to reflect the adoption impact of ASC 606 and ASU 2016-18, which we adopted on February 1, 2018