Condensed Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Initial Public Offering	Private Placement	Series A Redeemable Convertible Preferred Stock	Series B Redeemable Convertible Preferred Stock	Series C Redeemable Convertible Preferred Stock	Common Stock	Common Stock Initial Public Offering	Common Stock Private Placement	Additional Paid-In Capital	Additional Paid-In Capital Initial Public Offering	Additional Paid-In Capital Private Placement	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2018	$ (71,469)						$ 1							$ (71,470)
Beginning balance, shares at Dec. 31, 2018				56,000,000	49,501,221
Beginning balance at Dec. 31, 2018				$ 61,516	$ 70,587
Beginning balance, shares at Dec. 31, 2018							1,363,000
Vesting of founders’ common stock and restricted stock awards	8									$ 8
Vesting of founders’ common stock and restricted stock awards, shares							126,057
Accretion to redemption value and cumulative dividends on redeemable convertible preferred stock					$ 1,344
Accretion to redemption value and cumulative dividends on redeemable convertible preferred stock	(1,344)									(320)				(1,024)
Stock-based compensation expense	312									312
Net unrealized gain (loss) on short-term investments	3												$ 3
Net income (loss)	(14,023)													(14,023)
Ending balance at Mar. 31, 2019	(86,513)						$ 1						3	(86,517)
Ending balance, shares at Mar. 31, 2019				56,000,000	49,501,221
Ending balance at Mar. 31, 2019				$ 61,516	$ 71,931
Ending balance, shares at Mar. 31, 2019							1,489,057
Beginning balance at Dec. 31, 2018	(71,469)						$ 1							(71,470)
Beginning balance, shares at Dec. 31, 2018				56,000,000	49,501,221
Beginning balance at Dec. 31, 2018				$ 61,516	$ 70,587
Beginning balance, shares at Dec. 31, 2018							1,363,000
Net unrealized gain (loss) on short-term investments	1
Net income (loss)	(42,800)
Ending balance at Sep. 30, 2019	(116,878)						$ 1						1	(116,880)
Ending balance, shares at Sep. 30, 2019				56,000,000	49,501,221
Ending balance at Sep. 30, 2019				$ 61,516	$ 74,665
Ending balance, shares at Sep. 30, 2019							1,773,999
Beginning balance at Mar. 31, 2019	(86,513)						$ 1						3	(86,517)
Beginning balance, shares at Mar. 31, 2019				56,000,000	49,501,221
Beginning balance at Mar. 31, 2019				$ 61,516	$ 71,931
Beginning balance, shares at Mar. 31, 2019							1,489,057
Vesting of founders’ common stock and restricted stock awards	9									9
Vesting of founders’ common stock and restricted stock awards, shares							139,363
Option exercises	132									132
Option exercises, shares							21,940
Accretion to redemption value and cumulative dividends on redeemable convertible preferred stock					$ 1,359
Accretion to redemption value and cumulative dividends on redeemable convertible preferred stock	(1,359)									(647)				(712)
Stock-based compensation expense	506									506
Net unrealized gain (loss) on short-term investments	8												8
Net income (loss)	(15,522)													(15,522)
Ending balance at Jun. 30, 2019	(102,739)						$ 1						11	(102,751)
Ending balance, shares at Jun. 30, 2019				56,000,000	49,501,221
Ending balance at Jun. 30, 2019				$ 61,516	$ 73,290
Ending balance, shares at Jun. 30, 2019							1,650,360
Vesting of founders’ common stock and restricted stock awards	7									7
Vesting of founders’ common stock and restricted stock awards, shares							116,865
Option exercises	14									14
Option exercises, shares							6,774
Accretion to redemption value and cumulative dividends on redeemable convertible preferred stock					$ 1,375
Accretion to redemption value and cumulative dividends on redeemable convertible preferred stock	(1,375)									(501)				(874)
Stock-based compensation expense	480									480
Net unrealized gain (loss) on short-term investments	(10)												(10)
Net income (loss)	(13,255)													(13,255)
Ending balance at Sep. 30, 2019	(116,878)						$ 1						1	(116,880)
Ending balance, shares at Sep. 30, 2019				56,000,000	49,501,221
Ending balance at Sep. 30, 2019				$ 61,516	$ 74,665
Ending balance, shares at Sep. 30, 2019							1,773,999
Beginning balance at Dec. 31, 2019	$ (76,295)						$ 1						(1)	(76,295)
Beginning balance, shares at Dec. 31, 2019	0			56,000,000	49,501,221	26,360,745
Beginning balance at Dec. 31, 2019				$ 62,468	$ 75,860	$ 47,947
Beginning balance, shares at Dec. 31, 2019	1,846,024						1,846,024
Issuance of Series C redeemable preferred stock, shares						28,527,313
Issuance of Series C redeemable preferred stock						$ 52,038
Vesting of founders’ common stock and restricted stock awards	$ 4									4
Vesting of founders’ common stock and restricted stock awards, shares							52,093
Option exercises	26									26
Option exercises, shares							8,252
Stock-based compensation expense	425									425
Net unrealized gain (loss) on short-term investments	60												60
Net income (loss)	11,029													11,029
Ending balance at Mar. 31, 2020	(64,751)						$ 1			455			59	(65,266)
Ending balance, shares at Mar. 31, 2020				56,000,000	49,501,221	54,888,058
Ending balance at Mar. 31, 2020				$ 62,468	$ 75,860	$ 99,985
Ending balance, shares at Mar. 31, 2020							1,906,349
Beginning balance at Dec. 31, 2019	$ (76,295)						$ 1						(1)	(76,295)
Beginning balance, shares at Dec. 31, 2019	0			56,000,000	49,501,221	26,360,745
Beginning balance at Dec. 31, 2019				$ 62,468	$ 75,860	$ 47,947
Beginning balance, shares at Dec. 31, 2019	1,846,024						1,846,024
Net unrealized gain (loss) on short-term investments	$ (17)
Net income (loss)	(22,506)
Ending balance at Sep. 30, 2020	$ 300,346						$ 3			399,162			(18)	(98,801)
Ending balance, shares at Sep. 30, 2020	0			0	0	0
Ending balance, shares at Sep. 30, 2020	35,465,715						35,465,715
Beginning balance at Mar. 31, 2020	$ (64,751)						$ 1			455			59	(65,266)
Beginning balance, shares at Mar. 31, 2020				56,000,000	49,501,221	54,888,058
Beginning balance at Mar. 31, 2020				$ 62,468	$ 75,860	$ 99,985
Beginning balance, shares at Mar. 31, 2020							1,906,349
Issuance of common/preferred stock		$ 148,400	$ 10,000					$ 1			$ 148,399	$ 10,000
Issuance of common/preferred stock, shares								10,350,000	625,000
Vesting of founders’ common stock and restricted stock awards	1									1
Vesting of founders’ common stock and restricted stock awards, shares							40,102
Option exercises	177									177
Option exercises, shares							73,719
Conversion of Series A, B, Cconvertible preferred stock tocommon stock	238,293						$ 1			238,292
Conversion of Series A, B, C convertible preferred stock to common stock, shares				(56,000,000)	(49,501,221)	(54,888,058)
Conversion of Series A, B, C convertible preferred stock to common stock				$ (62,468)	$ (75,860)	$ (99,985)
Conversion of Series A, B, C convertible preferred stock to common stock, shares							22,432,029
Stock-based compensation expense	786									786
Net unrealized gain (loss) on short-term investments	(89)												(89)
Net income (loss)	(17,001)													(17,001)
Ending balance at Jun. 30, 2020	315,816						$ 3			398,110			(30)	(82,267)
Ending balance, shares at Jun. 30, 2020							35,427,199
Additional issuance costs related to initial public offering		$ (123)									$ (123)
Vesting of founders’ common stock and restricted stock awards	3									3
Vesting of founders’ common stock and restricted stock awards, shares							38,058
Option exercises	3									3
Option exercises, shares							458
Stock-based compensation expense	1,169									1,169
Net unrealized gain (loss) on short-term investments	12												12
Net income (loss)	(16,534)													(16,534)
Ending balance at Sep. 30, 2020	$ 300,346						$ 3			$ 399,162			$ (18)	$ (98,801)
Ending balance, shares at Sep. 30, 2020	0			0	0	0
Ending balance, shares at Sep. 30, 2020	35,465,715						35,465,715