Condensed Consolidated Statement of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Redeemable Convertible Preferred Stock	Common Stock	Additional Pain In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2018	$ (33,516)		$ 1	$ 8,005	$ (41,509)	$ (13)
Balance, temporary equity, shares at Dec. 31, 2018		40,094,850
Balance, temporary equity at Dec. 31, 2018		$ 38,068
Balance, shares at Dec. 31, 2018			2,140,787
Issuance of redeemable convertible preferred stock		$ 88
Issuance of redeemable convertible preferred stock, shares		67,656
Issuance of common stock upon exercise of stock options	9			9
Issuance of common stock upon exercise of stock options, shares			4,300
Vesting of early exercised stock options	47			47
Stock-based compensation expense	251			251
Other comprehensive income	18					18
Net loss	(4,131)				(4,131)
Balance at Mar. 31, 2019	(37,322)		$ 1	8,312	(45,640)	5
Balance, temporary equity, shares at Mar. 31, 2019		40,162,506
Balance, temporary equity at Mar. 31, 2019		$ 38,156
Balance, shares at Mar. 31, 2019			2,145,087
Balance at Dec. 31, 2018	(33,516)		$ 1	8,005	(41,509)	(13)
Balance, temporary equity, shares at Dec. 31, 2018		40,094,850
Balance, temporary equity at Dec. 31, 2018		$ 38,068
Balance, shares at Dec. 31, 2018			2,140,787
Net loss	(21,560)
Unrealized (loss) gain on marketable debt securities, net of tax	11
Balance at Sep. 30, 2019	(54,129)		$ 1	8,941	(63,069)	(2)
Balance, temporary equity, shares at Sep. 30, 2019		97,166,921
Balance, temporary equity at Sep. 30, 2019		$ 114,212
Balance, shares at Sep. 30, 2019			2,152,268
Balance at Mar. 31, 2019	(37,322)		$ 1	8,312	(45,640)	5
Balance, temporary equity, shares at Mar. 31, 2019		40,162,506
Balance, temporary equity at Mar. 31, 2019		$ 38,156
Balance, shares at Mar. 31, 2019			2,145,087
Issuance of common stock upon exercise of stock options	7			7
Issuance of common stock upon exercise of stock options, shares			3,278
Stock-based compensation expense	223			223
Other comprehensive income	(2)					(2)
Net loss	(2,651)				(2,651)
Balance at Jun. 30, 2019	(39,745)		$ 1	8,542	(48,291)	3
Balance, temporary equity, shares at Jun. 30, 2019		40,162,506
Balance, temporary equity at Jun. 30, 2019		$ 38,156
Balance, shares at Jun. 30, 2019			2,148,365
Issuance of redeemable convertible preferred stock		$ 74,913
Issuance of redeemable convertible preferred stock, shares		57,004,415
Issuance of common stock upon exercise of stock options	8			8
Issuance of common stock upon exercise of stock options, shares			3,903
Termination of redeemable convertible preferred stock tranche liability		$ 1,143
Stock-based compensation expense	391			391
Other comprehensive income	(5)					(5)
Net loss	(14,778)				(14,778)
Unrealized (loss) gain on marketable debt securities, net of tax	(5)
Balance at Sep. 30, 2019	(54,129)		$ 1	8,941	(63,069)	(2)
Balance, temporary equity, shares at Sep. 30, 2019		97,166,921
Balance, temporary equity at Sep. 30, 2019		$ 114,212
Balance, shares at Sep. 30, 2019			2,152,268
Balance at Dec. 31, 2019	(60,366)			9,258	(69,647)	(23)
Balance, temporary equity, shares at Dec. 31, 2019		97,166,921
Balance, temporary equity at Dec. 31, 2019	114,083	$ 114,083
Balance, shares at Dec. 31, 2019			2,155,578
Issuance of common stock upon exercise of stock options	42			42
Issuance of common stock upon exercise of stock options, shares			19,947
Stock-based compensation expense	299			299
Net loss	(4,486)				(4,486)
Unrealized (loss) gain on marketable debt securities, net of tax	(15)					(15)
Balance at Mar. 31, 2020	(64,526)			9,599	(74,133)	8
Balance, temporary equity, shares at Mar. 31, 2020		97,166,921
Balance, temporary equity at Mar. 31, 2020		$ 114,083
Balance, shares at Mar. 31, 2020			2,175,525
Balance at Dec. 31, 2019	(60,366)			9,258	(69,647)	(23)
Balance, temporary equity, shares at Dec. 31, 2019		97,166,921
Balance, temporary equity at Dec. 31, 2019	114,083	$ 114,083
Balance, shares at Dec. 31, 2019			2,155,578
Conversion of redeemable convertible preferred stock warrants to common stock warrants	114,083
Net loss	(27,720)
Unrealized (loss) gain on marketable debt securities, net of tax	60
Balance at Sep. 30, 2020	116,930		$ 1	214,213	(97,367)	83
Balance, temporary equity, shares at Sep. 30, 2020		0
Balance, shares at Sep. 30, 2020			19,589,637
Balance at Mar. 31, 2020	(64,526)			9,599	(74,133)	8
Balance, temporary equity, shares at Mar. 31, 2020		97,166,921
Balance, temporary equity at Mar. 31, 2020		$ 114,083
Balance, shares at Mar. 31, 2020			2,175,525
Issuance of common stock upon exercise of stock options	7			7
Issuance of common stock upon exercise of stock options, shares			3,101
Stock-based compensation expense	351			351
Net loss	(8,455)				(8,455)
Unrealized (loss) gain on marketable debt securities, net of tax	189					189
Balance at Jun. 30, 2020	(72,434)			9,957	(82,588)	197
Balance, temporary equity, shares at Jun. 30, 2020		97,166,921
Balance, temporary equity at Jun. 30, 2020		$ 114,083
Balance, shares at Jun. 30, 2020			2,178,626
Issuance of common stock upon exercise of stock options	144			144
Issuance of common stock upon exercise of stock options, shares			100,092
Stock-based compensation expense	2,966			2,966
Conversion of shares of redeemable convertible preferred stock to shares of common stock in connection with the Merger	114,083		$ 1	114,082
Conversion of shares of redeemable convertible preferred stock to shares of common stock in connection with the Merger, shares		(97,166,921)
Conversion of shares of redeemable convertible preferred stock to shares of common stock in connection with the Merger		$ (114,083)
Conversion of shares of redeemable convertible preferred stock to shares of common stock in connection with the Merger, shares			12,048,671
Exchange of common stock in connection with the Merger	84,142			84,142
Exchange of common stock in connection with the Merger, shares			5,262,248
Conversion of redeemable convertible preferred stock warrants to common stock warrants	2,922			2,922
Net loss	(14,779)				(14,779)
Unrealized (loss) gain on marketable debt securities, net of tax	(114)					(114)
Balance at Sep. 30, 2020	$ 116,930		$ 1	$ 214,213	$ (97,367)	$ 83
Balance, temporary equity, shares at Sep. 30, 2020		0
Balance, shares at Sep. 30, 2020			19,589,637