Condensed Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Series A Redeemable Convertible Preferred Stock	Series B Redeemable Convertible Preferred Stock	Series C Redeemable Convertible Preferred Stock	Series D Redeemable Convertible Preferred Stock
Beginning balance at Dec. 31, 2019	$ (106,373)	$ 7	$ 2,967	$ (109,347)
Beginning balance, shares at Dec. 31, 2019		4,059,909
Beginning balance at Dec. 31, 2019						$ 24,967	$ 55,151	$ 80,192
Beginning balance, shares at Dec. 31, 2019						6,225,719	6,786,896	7,377,480
Exercise of stock options	49		49
Exercise of stock options (in shares)		28,837
Issuance of common stock related to early exercised stock options		14,819
Vesting of early exercised stock options	128		128
Issuance of preferred stock									$ 109,875
Issuance of preferred stock, net of issuance cost (in shares)									8,220,242
Stock-based compensation expense	372		372
Net Loss	(27,142)			(27,142)
Ending balance at Mar. 31, 2020	(132,966)	$ 7	3,516	(136,489)
Ending balance, shares at Mar. 31, 2020		4,103,565
Ending balance at Mar. 31, 2020						$ 24,967	$ 55,151	$ 80,192	$ 109,875
Ending balance, shares at Mar. 31, 2020						6,225,719	6,786,896	7,377,480	8,220,242
Beginning balance at Dec. 31, 2019	(106,373)	$ 7	2,967	(109,347)
Beginning balance, shares at Dec. 31, 2019		4,059,909
Beginning balance at Dec. 31, 2019						$ 24,967	$ 55,151	$ 80,192
Beginning balance, shares at Dec. 31, 2019						6,225,719	6,786,896	7,377,480
Net Loss	(68,480)
Ending balance at Sep. 30, 2020	364,075	$ 54	541,848	(177,827)
Ending balance, shares at Sep. 30, 2020		50,949,490
Beginning balance at Mar. 31, 2020	(132,966)	$ 7	3,516	(136,489)
Beginning balance, shares at Mar. 31, 2020		4,103,565
Beginning balance at Mar. 31, 2020						$ 24,967	$ 55,151	$ 80,192	$ 109,875
Beginning balance, shares at Mar. 31, 2020						6,225,719	6,786,896	7,377,480	8,220,242
Conversion of preferred stock	270,190	$ 29	270,161			$ (24,967)	$ (55,151)	$ (80,192)	$ (109,879)
Conversion of preferred stock (in shares)						(6,225,719)	(6,786,896)	(7,377,480)	(8,220,242)
Conversion of preferred stock (in shares)		28,610,337
Conversion of common stock warrant		30,278
Conversion of preferred stock warrant		16,591
Warrant liability write-off	629		629
Issuance of common stock upon initial public offering or at-the-market offering, net of issuance costs	264,079	$ 18	264,061
Issuance of common stock upon initial public offering or at-the-market offering, net of issuance costs (in shares)		17,968,750
Exercise of stock options	297		297
Exercise of stock options (in shares)		152,177
Vesting of early exercised stock options	12		12
Issuance costs		$ (3,296)
Issuance of preferred stock									$ 4
Stock-based compensation expense	1,289		1,289
Net Loss	(20,320)			(20,320)
Ending balance at Jun. 30, 2020	383,210	$ 54	539,965	(156,809)
Ending balance, shares at Jun. 30, 2020		50,881,698
Exercise of stock options	108		108
Exercise of stock options (in shares)		67,792
Vesting of early exercised stock options	9		9
Issuance costs	(72)		(72)
Stock-based compensation expense	1,838		1,838
Net Loss	(21,018)			(21,018)
Ending balance at Sep. 30, 2020	364,075	$ 54	541,848	(177,827)
Ending balance, shares at Sep. 30, 2020		50,949,490
Beginning balance at Dec. 31, 2020	345,843	$ 54	544,353	(198,564)
Beginning balance, shares at Dec. 31, 2020		51,071,593
Exercise of stock options	487		487
Exercise of stock options (in shares)		267,208
Vesting of early exercised stock options	9		9
Stock-based compensation expense	1,865		1,865
Unrealized gains (losses) on investments	(47)				$ (47)
Net Loss	(21,220)			(21,220)
Ending balance at Mar. 31, 2021	326,937	$ 54	546,714	(219,784)	(47)
Ending balance, shares at Mar. 31, 2021		51,338,801
Beginning balance at Dec. 31, 2020	345,843	$ 54	544,353	(198,564)
Beginning balance, shares at Dec. 31, 2020		51,071,593
Net Loss	(71,514)
Ending balance at Sep. 30, 2021	305,956	$ 56	575,990	(270,078)	(12)
Ending balance, shares at Sep. 30, 2021		52,587,855
Beginning balance at Mar. 31, 2021	326,937	$ 54	546,714	(219,784)	(47)
Beginning balance, shares at Mar. 31, 2021		51,338,801
Exercise of stock options	466		466
Exercise of stock options (in shares)		190,003
Vesting of early exercised stock options	2		2
Issuance of common stock under Employee Stock Purchase Plan	490		490
Issuance of common stock under Employee Stock Purchase Plan (in shares)		35,286
Issuance of common stock to Lonza Ltd.	10,001	$ 1	10,000
Issuance of common stock to Lonza Ltd. (in shares)		399,680
Stock-based compensation expense	2,769		2,769
Unrealized gains (losses) on investments	39				39
Net Loss	(23,679)			(23,679)
Ending balance at Jun. 30, 2021	317,025	$ 55	560,441	(243,463)	(8)
Ending balance, shares at Jun. 30, 2021		51,963,770
Issuance of common stock upon initial public offering or at-the-market offering, net of issuance costs	12,120	$ 1	12,119
Issuance of common stock upon initial public offering or at-the-market offering, net of issuance costs (in shares)		498,502
Exercise of stock options	491		491
Exercise of stock options (in shares)		125,583
Vesting of early exercised stock options	2		2
Issuance costs		$ (41)
Stock-based compensation expense	2,937		2,937
Unrealized gains (losses) on investments	(4)				(4)
Net Loss	(26,615)			(26,615)
Ending balance at Sep. 30, 2021	$ 305,956	$ 56	$ 575,990	$ (270,078)	$ (12)
Ending balance, shares at Sep. 30, 2021		52,587,855