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		9 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Numerator:
Net loss	$ (33,778)	$ (21,931)	$ (89,681)	$ (65,285)
Denominator:
Weighted-average shares outstanding - basic and diluted (in shares)	95,474	19,174	76,950	18,850
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	$ (0.35)	$ (1.14)	$ (1.17)	$ (3.46)
Class A Common Stock
Numerator:
Net loss	$ (8,858)	$ 0	$ (16,908)	$ 0
Denominator:
Weighted-average shares outstanding - basic and diluted (in shares)	25,039	0	14,508	0
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	$ (0.35)	$ 0.00	$ (1.17)	$ 0.00
Class B Common Stock
Numerator:
Net loss	$ (24,919)	$ (21,931)	$ (72,773)	$ (65,285)
Denominator:
Weighted-average shares outstanding - basic and diluted (in shares)	70,435	19,174	62,442	18,850
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	$ (0.35)	$ (1.14)	$ (1.17)	$ (3.46)