CONDENSED STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' DEFICIT - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Series A Redeemable Convertible Preferred Stock	Series B Redeemable Convertible Preferred Stock	Total
Beginning Balances at Dec. 31, 2019						$ 31,816
Beginning Balances (in shares) at Dec. 31, 2019						37,269,149
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of redeemable convertible preferred stock, net of issuance costs				$ 24,978
Issuance of redeemable convertible preferred stock, net of issuance costs (in shares)				24,015,368
Ending Balances at Mar. 31, 2020						$ 56,794
Ending Balances (in shares) at Mar. 31, 2020						61,284,517
Beginning Balances at Dec. 31, 2019		$ 470	$ (15,988)			$ (15,518)
Beginning Balances (in shares) at Dec. 31, 2019	1,004,310
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options		1				1
Issuance of common stock upon exercise of stock options (in shares)	522
Vesting of restricted common stock (in shares)	27,866
Vesting of early exercised options		3				3
Vesting of early exercised options (in shares)	3,352
Stock-based compensation		78				78
Net loss			(4,686)			(4,686)
Ending Balances at Mar. 31, 2020		552	(20,674)			(20,122)
Ending Balances (in shares) at Mar. 31, 2020	1,036,050
Beginning Balances at Dec. 31, 2019						$ 31,816
Beginning Balances (in shares) at Dec. 31, 2019						37,269,149
Ending Balances at Sep. 30, 2020						$ 81,658
Ending Balances (in shares) at Sep. 30, 2020						85,299,885
Beginning Balances at Dec. 31, 2019		470	(15,988)			$ (15,518)
Beginning Balances (in shares) at Dec. 31, 2019	1,004,310
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss						(17,850)
Ending Balances at Sep. 30, 2020		790	(33,838)			(33,048)
Ending Balances (in shares) at Sep. 30, 2020	1,153,633
Beginning Balances at Mar. 31, 2020						$ 56,794
Beginning Balances (in shares) at Mar. 31, 2020						61,284,517
Ending Balances at Jun. 30, 2020						$ 56,794
Ending Balances (in shares) at Jun. 30, 2020						61,284,517
Beginning Balances at Mar. 31, 2020		552	(20,674)			$ (20,122)
Beginning Balances (in shares) at Mar. 31, 2020	1,036,050
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options		83				83
Issuance of common stock upon exercise of stock options (in shares)	54,452
Vesting of restricted common stock (in shares)	27,866
Vesting of early exercised options		3				3
Vesting of early exercised options (in shares)	3,700
Stock-based compensation		74				74
Net loss			(6,174)			(6,174)
Ending Balances at Jun. 30, 2020		712	(26,848)			(26,136)
Ending Balances (in shares) at Jun. 30, 2020	1,122,068
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of redeemable convertible preferred stock, net of issuance costs				$ 24,864
Issuance of redeemable convertible preferred stock, net of issuance costs (in shares)				24,015,368
Ending Balances at Sep. 30, 2020						$ 81,658
Ending Balances (in shares) at Sep. 30, 2020						85,299,885
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted common stock (in shares)	27,865
Vesting of early exercised options		3				$ 3
Vesting of early exercised options (in shares)	3,700
Stock-based compensation		75				75
Net loss			(6,990)			(6,990)
Ending Balances at Sep. 30, 2020		790	(33,838)			(33,048)
Ending Balances (in shares) at Sep. 30, 2020	1,153,633
Beginning Balances at Dec. 31, 2020				$ 79,597		$ 81,658
Beginning Balances (in shares) at Dec. 31, 2020				82,879,139		85,299,885
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of redeemable convertible preferred stock, net of issuance costs					$ 115,831
Issuance of redeemable convertible preferred stock, net of issuance costs (in shares)					53,522,099
Ending Balances at Mar. 31, 2021						$ 197,489
Ending Balances (in shares) at Mar. 31, 2021						138,821,984
Beginning Balances at Dec. 31, 2020		1,021	(42,511)			$ (41,490)
Beginning Balances (in shares) at Dec. 31, 2020	1,244,139
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options		29				29
Issuance of common stock upon exercise of stock options (in shares)	16,453
Vesting of restricted common stock (in shares)	4,326
Vesting of early exercised options		8				8
Vesting of early exercised options (in shares)	6,529
Stock-based compensation		164				164
Net loss			(8,380)			(8,380)
Ending Balances at Mar. 31, 2021		1,222	(50,891)			(49,669)
Ending Balances (in shares) at Mar. 31, 2021	1,271,447
Beginning Balances at Dec. 31, 2020				$ 79,597		$ 81,658
Beginning Balances (in shares) at Dec. 31, 2020				82,879,139		85,299,885
Ending Balances at Sep. 30, 2021				$ 79,597	$ 115,831	$ 197,489
Ending Balances (in shares) at Sep. 30, 2021				82,879,139	53,522,099	138,821,984
Beginning Balances at Dec. 31, 2020		1,021	(42,511)			$ (41,490)
Beginning Balances (in shares) at Dec. 31, 2020	1,244,139
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss						(32,711)
Ending Balances at Sep. 30, 2021		2,631	(75,222)			(72,591)
Ending Balances (in shares) at Sep. 30, 2021	1,547,774
Beginning Balances at Mar. 31, 2021						$ 197,489
Beginning Balances (in shares) at Mar. 31, 2021						138,821,984
Ending Balances at Jun. 30, 2021						$ 197,489
Ending Balances (in shares) at Jun. 30, 2021						138,821,984
Beginning Balances at Mar. 31, 2021		1,222	(50,891)			$ (49,669)
Beginning Balances (in shares) at Mar. 31, 2021	1,271,447
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options		212				212
Issuance of common stock upon exercise of stock options (in shares)	119,359
Vesting of restricted common stock (in shares)	4,327
Vesting of early exercised options		18				18
Vesting of early exercised options (in shares)	10,592
Stock-based compensation		326				326
Net loss			(9,901)			(9,901)
Ending Balances at Jun. 30, 2021		1,778	(60,792)			(59,014)
Ending Balances (in shares) at Jun. 30, 2021	1,405,725
Ending Balances at Sep. 30, 2021				$ 79,597	$ 115,831	$ 197,489
Ending Balances (in shares) at Sep. 30, 2021				82,879,139	53,522,099	138,821,984
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options		106				$ 106
Issuance of common stock upon exercise of stock options (in shares)	57,661
Vesting of restricted common stock (in shares)	2,884
Vesting of early exercised options		170				170
Vesting of early exercised options (in shares)	81,504
Stock-based compensation		577				577
Net loss			(14,430)			(14,430)
Ending Balances at Sep. 30, 2021		$ 2,631	$ (75,222)			$ (72,591)
Ending Balances (in shares) at Sep. 30, 2021	1,547,774