Consolidated Statements of Convertible Preferred Stock and Stockholders' Deficit - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Notes Receivable from Stockholders	Accumulated Other Comprehensive Loss	Accumulated Deficit	Treasury Stock
Beginning Balance at Jan. 31, 2015	$ (121,400)		$ 1	$ 11,464	$ (766)	$ (151)	$ (131,948)
Temporary equity Beginning Balance, Shares at Jan. 31, 2015		7,782,781
Temporary equity Beginning Balance at Jan. 31, 2015		$ 134,371
Beginning Balance, Shares at Jan. 31, 2015			3,131,353
Issuance of Series F Convertible Preferred Stock at $44.04 per share for cash, net of issuance costs of $1,784		$ 122,770
Issuance of Series F Convertible Preferred Stock at $7.34 per share for cash, net of issuance costs of $1,784, Shares		2,828,185
Issuance of common stock upon exercise of stock options	3,132			3,132
Issuance of common stock upon exercise of stock options, Shares			329,717
Repurchase of unvested early exercised stock options	(5)			(5)
Repurchase of unvested early exercised stock options, Shares			(1,702)
Vesting of early exercise of stock options	23			23
Vesting of stock options exercised with notes receivable				556	(556)
Accrued interest for notes receivable from stockholders	(39)				(39)
Stock-based compensation	9,755			9,755
Repurchase of common stock by way of note forgiveness	0
Other comprehensive loss	(55)					(55)
Net loss	(100,968)						(100,968)
Ending Balance at Jan. 31, 2016	(209,557)		$ 1	24,925	(1,361)	(206)	(232,916)
Temporary equity Ending Balance, Shares at Jan. 31, 2016		10,610,966
Temporary equity Ending Balance at Jan. 31, 2016		$ 257,141
Ending Balance, Shares at Jan. 31, 2016			3,459,368
Issuance of common stock upon exercise of stock options	2,292			2,292
Issuance of common stock upon exercise of stock options, Shares			168,380
Vesting of early exercise of stock options	65			65
Vesting of stock options exercised with notes receivable				558	(558)
Proceeds from repayment of notes receivable from stockholder	411				411
Accrued interest for notes receivable from stockholders	(36)				(36)
Stock-based compensation	13,834			13,834
Repurchase of common stock by way of note forgiveness	0
Excess tax benefit from stock-based compensation	71			71
Other comprehensive loss	(260)					(260)
Net loss	(105,801)						(105,801)
Ending Balance at Jan. 31, 2017	$ (298,981)		$ 1	41,745	(1,544)	(466)	(338,717)
Temporary equity Ending Balance, Shares at Jan. 31, 2017	10,610,966	10,610,966
Temporary equity Ending Balance at Jan. 31, 2017	$ 257,141	$ 257,141
Ending Balance, Shares at Jan. 31, 2017			3,627,748
Issuance of common stock upon exercise of stock options	$ 470			470
Issuance of common stock upon exercise of stock options, Shares	219,896		33,011
Early exercise of stock options	$ (665)			(665)
Vesting of early exercise of stock options	891			891
Vesting of stock options exercised with notes receivable				231	(231)
Proceeds from initial public offering, net of underwriting discounts and commissions	62,314			62,314
Proceeds from initial public offering, net of underwriting discounts and commisions, Shares			9,572,000
Payment of offering costs	(6,601)			(6,601)
Accrued interest for notes receivable from stockholders	(19)				(19)
Repayment of notes receivable from stockholder through repurchase of common stock, Shares			186,885
Stock-based compensation	51,818			51,818
Impact of adjustment to Series E, E-1, and F ConvertiblePreferred Stock	26,336						26,336
Impact of adjustment to Series E, E-1, and F ConvertiblePreferred Stock		$ (26,336)
Reclassification of convertible preferred stock warrant liabilityto additional paid in capital	375			375
Conversion of convertible preferred stock to common stock	237,393		$ 1	237,392
Conversion of convertible preferred stock to common stock, Shares		(10,610,966)
Conversion of convertible preferred stock to common stock		$ (237,393)
Conversion of convertible preferred stock to common stock, Shares			17,992,973
Repurchase of common stock by way of note forgiveness	(1,211)							$ (1,211)
Repurchase of common stock by way of note forgiveness, Shares			(88,520)
Repayment of executive employee promissory notes throughrepurchase of common stock					1,044
Repurchase of common stock by way of note forgiveness, Net	(167)
Deemed dividend to Series E and E-1 Convertible Preferred Stock	(6,588)						(6,588)
Deemed dividend to Series E and E-1 Convertible Preferred Stock		$ 6,588
Stock-based compensation reversal due to restructuring	(738)			(738)
Other comprehensive loss	111					111
Net loss	(157,659)						(157,659)
Ending Balance at Jan. 31, 2018	$ (91,710)		$ 2	$ 387,232	$ (750)	$ (355)	$ (476,628)	$ (1,211)
Temporary equity Ending Balance, Shares at Jan. 31, 2018	0
Ending Balance, Shares at Jan. 31, 2018			31,324,097