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)			3,786,375
Issuance of common stock upon exercise of stock options	676		$ 4	672
Stock-based compensation expense	1,975			1,975
Other comprehensive income (loss)	57				57
Net income	2,485					2,485
Ending balance (in shares) at Jul. 31, 2018		152,665,804	86,396,013
Ending balance at Jul. 31, 2018	(21,478)	$ 159,552	$ 84	9,164	(474)	(30,252)
Beginning balance (in shares) at Apr. 30, 2018		152,665,804	83,122,778
Beginning balance at Apr. 30, 2018	(27,006)	$ 159,552	$ 81	7,603	(613)	(34,077)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)			3,273,235
Issuance of common stock upon exercise of stock options	438		$ 3	435
Stock-based compensation expense	1,126			1,126
Other comprehensive income (loss)	139				139
Net income	3,825					3,825
Ending balance (in shares) at Jul. 31, 2018		152,665,804	86,396,013
Ending balance at Jul. 31, 2018	(21,478)	$ 159,552	$ 84	9,164	(474)	(30,252)
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)	14,272,059
Issuance of common stock upon exercise of stock options, net of repurchases (in shares)			13,747,059
Issuance of common stock upon exercise of stock options	$ 2,174		$ 14	2,160
Issuance of common stock reserved for charitable donation (in shares)			500,000
Issuance of common stock reserved for charitable donation	0
Stock-based compensation expense	24,844			24,844
Other comprehensive income (loss)	67				67
Net income	7,755					7,755
Ending balance (in shares) at Jul. 31, 2019		0	273,486,167
Ending balance at Jul. 31, 2019	743,796	$ 0	$ 272	760,990	(68)	(17,398)
Beginning balance (in shares) at Apr. 30, 2019		0	272,336,862
Beginning balance at Apr. 30, 2019	719,728	$ 0	$ 271	742,388	8	(22,939)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)			649,305
Issuance of common stock upon exercise of stock options	421		$ 1	420
Issuance of common stock reserved for charitable donation (in shares)			500,000
Issuance of common stock reserved for charitable donation	0
Stock-based compensation expense	18,182			18,182
Other comprehensive income (loss)	(76)				(76)
Net income	5,541					5,541
Ending balance (in shares) at Jul. 31, 2019		0	273,486,167
Ending balance at Jul. 31, 2019	$ 743,796	$ 0	$ 272	$ 760,990	$ (68)	$ (17,398)