Net Loss per Share - Summary of Computation 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	$ (154,960)	$ (151,787)	$ (202,948)
Denominator:
Weighted-average number of shares outstanding—basic and diluted	133,932	127,469	121,240
Net loss per share—basic and diluted	$ (1.16)	$ (1.19)	$ (1.67)
Class A Common Stock
Numerator:
Net loss	$ (115,847)	$ (64,771)	$ (49,448)
Denominator:
Weighted-average number of shares outstanding—basic and diluted	100,127	54,394	29,540
Net loss per share—basic and diluted	$ (1.16)	$ (1.19)	$ (1.67)
Class B Common Stock
Numerator:
Net loss	$ (39,113)	$ (87,016)	$ (153,500)
Denominator:
Weighted-average number of shares outstanding—basic and diluted	33,805	73,075	91,700
Net loss per share—basic and diluted	$ (1.16)	$ (1.19)	$ (1.67)