CONDENSED CONSOLIDATED STATEMENT OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' DEFICIT - 9 months ended Oct. 31, 2017 - USD ($) $ in Thousands	Total	Class A and Class B Common Stock	Additional Paid-In Capital	Treasury Stock	Accumulated Other Comprehensive Loss	Accumulated Deficit
Preferred stock, beginning balance (in shares) at Jan. 31, 2017	41,148,282
Beginning Balance, Redeemable Convertible Preferred Stock at Jan. 31, 2017	$ 345,257
Increase (Decrease) in Temporary Equity [Roll Forward]
Exercise of common stock warrants (in shares)	85,170
Exercise of preferred stock warrants	$ 1,171
Conversion of redeemable convertible preferred stock to common stock (in shares)	(41,233,452)
Conversion of redeemable convertible preferred stock to common stock	$ (346,428)
Preferred stock, beginning balance (in shares) at Oct. 31, 2017	0
Ending Balance, Redeemable Convertible Preferred Stock at Oct. 31, 2017	$ 0
Common stock, beginning balance (in shares) at Jan. 31, 2017		13,093,621
Beginning balance at Jan. 31, 2017	(286,514)	$ 13	$ 62,557	$ (1,319)	$ (364)	$ (347,401)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock warrants (in shares)		99,534
Exercise of common stock warrants	$ 1	$ 1
Stock option exercises (in shares)	1,242,172	1,242,172
Stock option exercises (in shares)	$ 5,471	$ 1	5,470
Repurchase of early exercised options (in shares)		(21,721)
Conversion of redeemable convertible preferred stock to common stock (in shares)		26,953,404
Conversion of redeemable convertible preferred stock to common stock	346,428	$ 27	346,401
Issuance of common stock upon initial public offering, net (in shares)		9,200,000
Issuance of common stock upon initial public offering, net	201,620	$ 9	201,611
Vesting of early exercised stock options	950		950
Stock-based compensation	15,066		15,066
Unrealized gain on available-for-sale securities	(33)				(33)
Foreign currency translation adjustment	181				181
Net loss	(69,985)					(69,985)
Common stock, ending balance (in shares) at Oct. 31, 2017		50,567,010
Ending balance at Oct. 31, 2017	$ 213,185	$ 51	$ 632,055	$ (1,319)	$ (216)	$ (417,386)