Stockholders' Equity - Additional Information (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Jan. 31, 2018 USD ($) vote class $ / shares shares	Jan. 31, 2017 $ / shares shares	Oct. 31, 2015 shares	Sep. 30, 2015 shares
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)	20,000,000	20,000,000	20,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Number of classes of stock | class	2
Common stock, shares authorized (in shares)	2,250,000,000	2,250,000,000
Common stock, shares issued (in shares)	220,979,000	204,364,000
Common stock, shares outstanding (in shares)	220,979,000	204,364,000
Convertible stock, automatic conversion, period after founders death	9 months
Convertible stock, automatic conversion, period after IPO	10 years
Class A common stock
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	2,000,000,000	2,000,000,000
Common stock, par value per share (in dollars per share) | $ / shares	$ 0.0001	$ 0.0001
Common stock, shares issued (in shares)	129,502,242	87,027,000
Common stock, shares outstanding (in shares)	129,502,000	87,027,000
Common stock, entitled votes per share (in votes per share) | vote	1
Class B common stock
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	250,000,000	250,000,000
Common stock, par value per share (in dollars per share) | $ / shares	$ 0.0001	$ 0.0001
Common stock, shares issued (in shares)	91,476,735	117,337,000
Common stock, shares outstanding (in shares)	91,477,000	117,337,000
Common stock, entitled votes per share (in votes per share) | vote	10
Convertible stock, automatic conversion, portion of outstanding stock, percentage	10.00%
Class B common stock | Pure Good Foundation
Class of Stock [Line Items]
Common stock, shares issued (in shares)				700,000
Non cash general and administrative expense | $	$ 11.9