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, 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]
Issuance of common stock upon exercise of stock options (in shares)		(152,665,804)	152,665,804
Issuance of common stock upon exercise of stock options	159,552	$ (159,552)	$ 153	159,399
Conversion of convertible preferred stock to common stock upon initial public offering (in shares)			426,223
Issuance of common stock upon exercise of stock options	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, net of repurchases (in shares)			13,747,059
Issuance of common stock upon exercise of stock options, net of repurchases	$ 2,174		$ 14	2,160
Issuance of common stock reserved for charitable donation (in shares)	500,000
Charitable donation of common stock	$ 0
Stock-based compensation expense	24,844			24,844
Other comprehensive income	67				67
Net income (loss)	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]
Conversion of convertible preferred stock to common stock upon initial public offering (in shares)			649,305
Issuance of common stock upon exercise of stock options	421		$ 1	420
Issuance of common stock upon release of restricted stock units (in shares)			500,000
Issuance of common stock upon release of restricted stock units	0			0
Stock-based compensation expense	18,182			18,182
Other comprehensive income	(76)				(76)
Net income (loss)	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)
Beginning balance (in shares) at Jan. 31, 2020		0	278,731,143
Beginning balance at Jan. 31, 2020	$ 833,943	$ 0	$ 277	832,705	809	152
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)	4,830,752
Issuance of common stock for employee stock purchase plan (in shares)			605,924
Issuance of common stock for employee stock purchase plan	$ 20,760		$ 1	20,759
Conversion of convertible preferred stock to common stock upon initial public offering (in shares)			4,830,752
Issuance of common stock upon exercise of stock options	17,681		$ 5	17,676
Issuance of common stock upon release of restricted stock units (in shares)			174,900
Issuance of common stock upon release of restricted stock units	0
Issuance of common stock upon exercise of stock options, net of repurchases	23,312			23,312
Charitable donation of common stock	88,089			88,089
Stock-based compensation expense	1,963				1,963
Net income (loss)	213,064					213,064
Ending balance (in shares) at Jul. 31, 2020		0	284,342,719
Ending balance at Jul. 31, 2020	1,198,812	$ 0	$ 283	982,541	2,772	213,216
Beginning balance (in shares) at Apr. 30, 2020		0	281,992,011
Beginning balance at Apr. 30, 2020	901,631	$ 0	$ 280	872,237	1,887	27,227
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)			1,597,761
Issuance of common stock upon exercise of stock options	7,956		$ 2	7,954
Issuance of common stock upon release of restricted stock units (in shares)			147,023
Issuance of common stock upon release of restricted stock units	0
Issuance of common stock for employee stock purchase plan (in shares)			605,924
Issuance of common stock for employee stock purchase plan	20,760		$ 1	20,759
Charitable donation of common stock	22,312			22,312
Stock-based compensation expense	59,279			59,279
Other comprehensive income	885				885
Net income (loss)	185,989					185,989
Ending balance (in shares) at Jul. 31, 2020		0	284,342,719
Ending balance at Jul. 31, 2020	$ 1,198,812	$ 0	$ 283	$ 982,541	$ 2,772	$ 213,216