Condensed Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Redeemable Convertible Preferred Stock	Follow-on Public Offering	Private Placement	Initial Public Offering	Common Stock	Common Stock Follow-on Public Offering	Common Stock Private Placement	Common Stock Initial Public Offering	Additional Paid-In Capital	Additional Paid-In Capital Follow-on Public Offering	Additional Paid-In Capital Private Placement	Additional Paid-In Capital Initial Public Offering	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2018	$ (48,948)									$ 1,599				$ (31)	$ (50,516)
Beginning balance, shares at Dec. 31, 2018						1,335,690
Redeemable convertible preferred stock, beginning balance, shares at Dec. 31, 2018		13,139,794
Redeemable convertible preferred stock, beginning balance at Dec. 31, 2018		$ 138,391
Issuance of common stock, net of issuance costs					$ 50,247				$ 1				$ 50,246
Issuance of common stock, net of issuance costs, shares									5,750,000
Issuance of common stock upon exercise of stock options	$ 261									261
Issuance of common stock upon exercise of stock options, shares						114,890
Repurchase of early exercised shares, shares	(14,244)					(14,244)
Vesting of early exercised common stock options and restricted stock	$ 91									91
Stock-based compensation	1,449									1,449
Other comprehensive income (loss)	109													109
Net loss	(31,194)														(31,194)
Ending balance at Sep. 30, 2019	110,406					$ 2				192,036				78	(81,710)
Ending balance, shares at Sep. 30, 2019						20,328,242
Conversion of redeemable convertible preferred stock into common stock	138,391					$ 1				138,390
Conversion of redeemable convertible preferred stock into common stock, shares		(13,139,794)
Conversion of redeemable convertible preferred stock into common stock		$ (138,391)
Conversion of redeemable convertible preferred stock into common stock, shares						13,139,794
Early exercised common stock options, shares						2,112
Beginning balance at Jun. 30, 2019	120,608					$ 2				191,310				37	(70,741)
Beginning balance, shares at Jun. 30, 2019						20,268,103
Issuance of common stock upon exercise of stock options	190									190
Issuance of common stock upon exercise of stock options, shares						62,501
Repurchase of early exercised shares, shares						(2,362)
Vesting of early exercised common stock options and restricted stock	18									18
Stock-based compensation	518									518
Other comprehensive income (loss)	41													41
Net loss	(10,969)														(10,969)
Ending balance at Sep. 30, 2019	110,406					$ 2				192,036				78	(81,710)
Ending balance, shares at Sep. 30, 2019						20,328,242
Beginning balance at Dec. 31, 2019	100,400					$ 2				192,824				65	(92,491)
Beginning balance, shares at Dec. 31, 2019						20,339,461
Issuance of common stock, net of issuance costs			$ 100,664	$ 19,988			$ 1				$ 100,663	$ 19,988
Issuance of common stock, net of issuance costs, shares							7,166,667	1,333,333
Issuance of common stock upon exercise of stock options	1,028									1,028
Issuance of common stock upon exercise of stock options, shares						218,724
Employee stock purchase plan (ESPP) purchase	$ 132									132
Employee stock purchase plan (ESPP) purchase, shares						18,494
Repurchase of early exercised shares, shares	(10,518)					(10,518)
Vesting of early exercised common stock options and restricted stock	$ 44									44
Stock-based compensation	2,563									2,563
Other comprehensive income (loss)	(30)													(30)
Net loss	(29,360)														(29,360)
Ending balance at Sep. 30, 2020	195,429					$ 3				317,242				35	(121,851)
Ending balance, shares at Sep. 30, 2020						29,066,161
Beginning balance at Jun. 30, 2020	172,058					$ 3				288,923				57	(116,925)
Beginning balance, shares at Jun. 30, 2020						27,184,824
Issuance of common stock, net of issuance costs			$ 7,040	$ 19,988							$ 7,040	$ 19,988
Issuance of common stock, net of issuance costs, shares							500,000	1,333,333
Issuance of common stock upon exercise of stock options	297									297
Issuance of common stock upon exercise of stock options, shares						53,353
Repurchase of early exercised shares, shares						(5,349)
Vesting of early exercised common stock options and restricted stock	13									13
Stock-based compensation	981									981
Other comprehensive income (loss)	(22)													(22)
Net loss	(4,926)														(4,926)
Ending balance at Sep. 30, 2020	$ 195,429					$ 3				$ 317,242				$ 35	$ (121,851)
Ending balance, shares at Sep. 30, 2020						29,066,161