Net Loss Per Share - Schedule of Basic and Diluted Net Loss Per Share (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
Numerator:
Net loss	$ (27,002)	$ (20,601)	$ (55,903)	$ (43,354)
Denominator:
Weighted-average shares outstanding - basic and diluted (in shares)	93,576	18,802	67,125	18,687
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	$ (0.29)	$ (1.10)	$ (0.83)	$ (2.32)
Class A Common Stock
Numerator:
Net loss	$ (4,227)	$ 0	$ (7,546)	$ 0
Denominator:
Weighted-average shares outstanding - basic and diluted (in shares)	14,650	0	9,061	0
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	$ (0.29)	$ 0.00	$ (0.83)	$ 0.00
Class B Common Stock
Numerator:
Net loss	$ (22,775)	$ (20,601)	$ (48,357)	$ (43,354)
Denominator:
Weighted-average shares outstanding - basic and diluted (in shares)	78,926	18,802	58,064	18,687
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	$ (0.29)	$ (1.10)	$ (0.83)	$ (2.32)