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 (Loss) Income	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)			16,487,350
Issuance of common stock upon exercise of stock options, net of repurchases	$ 6,019		$ 17	6,002
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	46,790			46,790
Other comprehensive income (loss)	786				786
Net income	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]
Conversion of convertible preferred stock to common stock upon initial public offering (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 (loss)	719				719
Net income	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)
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)	6,164,676
Issuance of common stock for employee stock purchase plan (in shares)			605,924
Conversion of convertible preferred stock to common stock upon initial public offering (in shares)			6,164,676
Issuance of common stock upon exercise of stock options	$ 24,291		$ 6	24,285
Issuance of common stock upon release of restricted stock units (in shares)			443,836
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
Issuance of common stock for employee stock purchase plan	20,760		$ 1	20,759
Stock-based compensation expense	185,398			185,398
Other comprehensive income (loss)	508				508
Net income	411,706					411,706
Ending balance (in shares) at Oct. 31, 2020		0	285,945,579
Ending balance at Oct. 31, 2020	1,499,918	$ 0	$ 284	1,086,459	1,317	411,858
Beginning balance (in shares) at Jul. 31, 2020		0	284,342,719
Beginning balance at Jul. 31, 2020	1,198,812	$ 0	$ 283	982,541	2,772	213,216
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)			1,333,924
Issuance of common stock upon exercise of stock options	6,610		$ 1	6,609
Issuance of common stock upon release of restricted stock units (in shares)			268,936
Issuance of common stock upon release of restricted stock units	0
Stock-based compensation expense	97,309			97,309
Other comprehensive income (loss)	(1,455)				(1,455)
Net income	198,642					198,642
Ending balance (in shares) at Oct. 31, 2020		0	285,945,579
Ending balance at Oct. 31, 2020	$ 1,499,918	$ 0	$ 284	$ 1,086,459	$ 1,317	$ 411,858