Net Loss Per Share - Schedule of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Numerator:
Net loss	$ (114,359)	$ (83,509)	$ (76,302)
Denominator:
Weighted-average shares outstanding, basic and diluted (in shares)	83,004	19,038	17,817
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (1.38)	$ (4.39)	$ (4.28)
Class A Common Stock
Denominator:
Weighted-average shares outstanding, basic and diluted (in shares)	24,165	0	0
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (1.38)	$ 0.00	$ 0.00
Class B Common Stock
Denominator:
Weighted-average shares outstanding, basic and diluted (in shares)	58,839	19,038	17,817
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (1.38)	$ (4.39)	$ (4.28)
Common Stock | Class A Common Stock
Numerator:
Net loss	$ (33,293)	$ 0	$ 0
Common Stock | Class B Common Stock
Numerator:
Net loss	$ (81,066)	$ (83,509)	$ (76,302)