CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance (in shares) at Jan. 31, 2018		152,665,804	82,609,638
Beginning balance at Jan. 31, 2018	$ (26,671)	$ 159,552	$ 80	$ 6,517	$ (531)	$ (32,737)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)			6,145,184
Issuance of common stock upon exercise of stock options	1,406		$ 7	1,399
Stock-based compensation expense	4,627			4,627
Other comprehensive income	142				142
Net income (loss)	1,887					1,887
Ending balance (in shares) at Oct. 31, 2018		152,665,804	88,754,822
Ending balance at Oct. 31, 2018	(18,609)	$ 159,552	$ 87	12,543	(389)	(30,850)
Beginning balance (in shares) at Jul. 31, 2018		152,665,804	86,396,013
Beginning balance at Jul. 31, 2018	(21,478)	$ 159,552	$ 84	9,164	(474)	(30,252)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)			2,358,809
Issuance of common stock upon exercise of stock options	730		$ 3	727
Stock-based compensation expense	2,652			2,652
Other comprehensive income	85				85
Net income (loss)	(598)					(598)
Ending balance (in shares) at Oct. 31, 2018		152,665,804	88,754,822
Ending balance at Oct. 31, 2018	(18,609)	$ 159,552	$ 87	12,543	(389)	(30,850)
Beginning balance (in shares) at Jan. 31, 2019		152,665,804	90,327,435
Beginning balance at Jan. 31, 2019	(7,439)	$ 159,552	$ 89	17,760	(135)	(25,153)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of convertible preferred stock to common stock upon initial public offering (in shares)		(152,665,804)	152,665,804
Conversion of convertible preferred stock to common stock upon initial public offering	159,552	$ (159,552)	$ 153	159,399
Conversion of convertible promissory notes and accrued interest to common stock upon initial public offering (in shares)			426,223
Conversion of convertible promissory notes and accrued interest to common stock upon initial public offering	15,344			15,344
Issuance of common stock upon initial public offering and private placement net of underwriting discounts and commissions and other offering costs (in shares)			15,819,646
Issuance of common stock upon initial public offering and private placement, net of underwriting discounts and commissions and other offering costs	$ 541,499		$ 16	541,483
Issuance of common stock upon exercise of stock options (in shares)	17,012,350
Issuance of common stock upon exercise of stock options, net of repurchases (in shares)			16,487,350
Issuance of common stock upon exercise of stock options	$ 6,019		$ 17	6,002
Issuance of common stock reserved for charitable donation (in shares)			500,000
Issuance of common stock reserved for charitable donations	0
Stock-based compensation expense	46,790			46,790
Other comprehensive income	786				786
Net income (loss)	9,966					9,966
Ending balance (in shares) at Oct. 31, 2019		0	276,226,458
Ending balance at Oct. 31, 2019	772,517	$ 0	$ 275	786,778	651	(15,187)
Beginning balance (in shares) at Jul. 31, 2019		0	273,486,167
Beginning balance at Jul. 31, 2019	743,796	$ 0	$ 272	760,990	(68)	(17,398)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)			2,740,291
Issuance of common stock upon exercise of stock options	3,845		$ 3	3,842
Stock-based compensation expense	21,946			21,946
Other comprehensive income	719				719
Net income (loss)	2,211					2,211
Ending balance (in shares) at Oct. 31, 2019		0	276,226,458
Ending balance at Oct. 31, 2019	$ 772,517	$ 0	$ 275	$ 786,778	$ 651	$ (15,187)