CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) - USD ($) $ in Thousands		Total	Redeemable convertible preferred stock		Common Stock		Additional Paid-in- Capital	Notes receivable from stockholders	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2019	[1]		4,384,348
Beginning balance at Dec. 31, 2019			$ 40,016
Ending balance (in shares) at Mar. 31, 2020	[1]		4,384,348
Ending balance at Mar. 31, 2020			$ 40,016
Beginning balance (in shares) at Dec. 31, 2019	[1]				7,902,407
Beginning balance at Dec. 31, 2019		$ (100,319)			$ 0		$ 2,320	$ (44)	$ (102,595)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)	[1]	423
Issuance of common stock upon exercise of stock options		$ 2					2
Vesting of early exercised stock options		12					12
Stock-based compensation expense		175					175
Net loss		(18,693)							(18,693)
Reclassification of a note receivable from a stockholder		44						44
Ending balance (in shares) at Mar. 31, 2020	[1]				7,902,830
Ending balance at Mar. 31, 2020		(118,779)					2,509	0	(121,288)
Beginning balance (in shares) at Dec. 31, 2019	[1]		4,384,348
Beginning balance at Dec. 31, 2019			$ 40,016
Ending balance (in shares) at Sep. 30, 2020	[1]		88,434,754
Ending balance at Sep. 30, 2020			$ 39,225
Beginning balance (in shares) at Dec. 31, 2019	[1]				7,902,407
Beginning balance at Dec. 31, 2019		(100,319)			$ 0		2,320	(44)	(102,595)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss		(49,620)
Ending balance (in shares) at Sep. 30, 2020	[1]				21,169,429
Ending balance at Sep. 30, 2020		(23,624)			$ 0		128,591	0	(152,215)
Beginning balance (in shares) at Mar. 31, 2020	[1]		4,384,348
Beginning balance at Mar. 31, 2020			$ 40,016
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of redeemable convertible preferred stock (in shares)	[1]		43,952,862
Issuance of redeemable convertible preferred stock			$ 18,330
Conversion of redeemable convertible preferred stock to common stock (in shares)	[1]		(4,384,348)
Conversion of redeemable convertible preferred stock to common stock			$ (40,016)
Ending balance (in shares) at Jun. 30, 2020	[1]		43,952,862
Ending balance at Jun. 30, 2020			$ 18,330
Beginning balance (in shares) at Mar. 31, 2020	[1]				7,902,830
Beginning balance at Mar. 31, 2020		(118,779)					2,509	0	(121,288)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of redeemable convertible preferred stock to common stock (in shares)	[1]				4,384,348
Conversion of redeemable convertible preferred stock to common stock		40,016			$ 0		40,016
Vesting of early exercised stock options		12					12
Stock-based compensation expense		460					460
Net loss		(11,312)							(11,312)
Conversion of convertible notes to common stock (in shares)	[1]				7,201,911
Conversion of convertible notes to common stock		78,311					78,311
Ending balance (in shares) at Jun. 30, 2020	[1]				19,489,089
Ending balance at Jun. 30, 2020		(11,292)			$ 0		121,308	0	(132,600)
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of redeemable convertible preferred stock (in shares)	[1]		44,481,892
Issuance of redeemable convertible preferred stock			$ 20,895
Ending balance (in shares) at Sep. 30, 2020	[1]		88,434,754
Ending balance at Sep. 30, 2020			$ 39,225
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)	[1]				63,076
Issuance of common stock upon exercise of stock options		7					7
Vesting of early exercised stock options		12					12
Stock-based compensation expense		7,256					7,256
Net loss		(19,615)							(19,615)
Issuance of common stock upon exercise of restricted stock awards (in shares)	[1]				1,617,264
Issuance of common stock upon exercise of restricted stock awards		8					8
Ending balance (in shares) at Sep. 30, 2020	[1]				21,169,429
Ending balance at Sep. 30, 2020		$ (23,624)			$ 0		128,591	0	(152,215)
Beginning balance (in shares) at Dec. 31, 2020		88,434,754	88,434,754	[1]
Beginning balance at Dec. 31, 2020		$ 39,225	$ 39,225
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of redeemable convertible preferred stock (in shares)	[1]		4,232,947
Issuance of redeemable convertible preferred stock			$ 58,097
Conversion of redeemable convertible preferred stock to common stock (in shares)	[1]		(92,667,701)
Conversion of redeemable convertible preferred stock to common stock			$ (97,322)
Ending balance (in shares) at Mar. 31, 2021	[1]		0
Ending balance at Mar. 31, 2021			$ 0
Beginning balance (in shares) at Dec. 31, 2020		33,327,294			33,327,294	[1]
Beginning balance at Dec. 31, 2020		$ (75,907)			$ 0		133,468	0	(209,375)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)	[1]				727,114
Issuance of common stock upon exercise of stock options		190			$ 1		189
Repurchase of common stock (shares)	[1]				(220,561)
Repurchase of common stock		(43)					(43)
Conversion of redeemable convertible preferred stock to common stock (in shares)	[1]				92,667,701
Conversion of redeemable convertible preferred stock to common stock		97,334			$ 12		97,322
Issuance of common stock upon merger and private offering, net of acquired private placement warrants of $19,377 (in shares)	[1]				34,947,657
Issuance of common stock upon merger and private offering, net of acquired private placement warrants of $19,377		272,064			$ 3		272,061
Offering costs in connection with the merger		(26,620)					(26,620)
Vesting of early exercised stock options		438					438
Stock-based compensation expense		5,256					5,256
Net loss		(20,957)							(20,957)
Ending balance (in shares) at Mar. 31, 2021	[1]				161,449,205
Ending balance at Mar. 31, 2021		$ 251,755			$ 16		482,071	0	(230,332)
Beginning balance (in shares) at Dec. 31, 2020		88,434,754	88,434,754	[1]
Beginning balance at Dec. 31, 2020		$ 39,225	$ 39,225
Ending balance (in shares) at Sep. 30, 2021		0	0	[1]
Ending balance at Sep. 30, 2021		$ 0	$ 0
Beginning balance (in shares) at Dec. 31, 2020		33,327,294			33,327,294	[1]
Beginning balance at Dec. 31, 2020		$ (75,907)			$ 0		133,468	0	(209,375)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		913,279
Net loss		$ (65,637)
Ending balance (in shares) at Sep. 30, 2021		161,529,449			161,529,449	[1]
Ending balance at Sep. 30, 2021		$ 220,580			$ 16		495,576	0	(275,012)
Beginning balance (in shares) at Mar. 31, 2021	[1]		0
Beginning balance at Mar. 31, 2021			$ 0
Ending balance (in shares) at Jun. 30, 2021	[1]		0
Ending balance at Jun. 30, 2021			$ 0
Beginning balance (in shares) at Mar. 31, 2021	[1]				161,449,205
Beginning balance at Mar. 31, 2021		251,755			$ 16		482,071	0	(230,332)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of early exercised stock options		104					104
Stock-based compensation expense		6,154					6,154
Net loss		(32,011)							(32,011)
Ending balance (in shares) at Jun. 30, 2021	[1]				161,449,205
Ending balance at Jun. 30, 2021		$ 226,002			$ 16		488,329	0	(262,343)
Ending balance (in shares) at Sep. 30, 2021		0	0	[1]
Ending balance at Sep. 30, 2021		$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)	[1]				186,165
Issuance of common stock upon exercise of stock options		35			$ 0		35
Cancellation of previously issued awards (in shares)					(105,921)
Vesting of early exercised stock options		65					65
Stock-based compensation expense		7,147					7,147
Net loss		$ (12,669)							(12,669)
Ending balance (in shares) at Sep. 30, 2021		161,529,449			161,529,449	[1]
Ending balance at Sep. 30, 2021		$ 220,580			$ 16		$ 495,576	$ 0	$ (275,012)

[1] The shares of the Company’s common and redeemable convertible preferred stock, prior to the Merger (as defined in Note 1), have been retroactively restated as shares reflecting the exchange ratio of approximately 0.703 established in the Merger as described in Note 1.