Condensed Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	IPO	Common Stock	Common Stock IPO	Additional Paid-in Capital	Additional Paid-in Capital IPO	Accumulated Deficit	Accumulated Other Comprehensive Income
Temporary equity, beginning balance (in shares) at Dec. 31, 2018	21,233,190
Temporary equity, beginning balance at Dec. 31, 2018	$ 105,235
Redeemable Convertible Preferred Stock
Exercise of Series C preferred stock warrants (in shares)	4,915
Exercise of Series C preferred stock warrants	$ 30
Temporary equity, ending balance (in shares) at Mar. 31, 2019	21,238,105
Temporary equity, ending balance at Mar. 31, 2019	$ 105,265
Beginning balance (in shares) at Dec. 31, 2018			1,135,310
Beginning balance at Dec. 31, 2018	(134,553)		$ 1		$ 4,557		$ (139,111)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)			251,305
Exercise of stock options	375				375
Stock-based compensation	262				262
Net loss and comprehensive loss	(24,158)						(24,158)
Ending balance (in shares) at Mar. 31, 2019			1,386,615
Ending balance at Mar. 31, 2019	$ (158,074)		$ 1		5,194		(163,269)
Temporary equity, beginning balance (in shares) at Dec. 31, 2018	21,233,190
Temporary equity, beginning balance at Dec. 31, 2018	$ 105,235
Temporary equity, ending balance (in shares) at Sep. 30, 2019	0
Temporary equity, ending balance at Sep. 30, 2019	$ 0
Beginning balance (in shares) at Dec. 31, 2018			1,135,310
Beginning balance at Dec. 31, 2018	(134,553)		$ 1		4,557		(139,111)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(44,124)
Net loss and comprehensive loss	(44,124)
Ending balance (in shares) at Sep. 30, 2019			30,775,980
Ending balance at Sep. 30, 2019	$ 77,443		$ 31		260,647		(183,235)
Temporary equity, beginning balance (in shares) at Mar. 31, 2019	21,238,105
Temporary equity, beginning balance at Mar. 31, 2019	$ 105,265
Redeemable Convertible Preferred Stock
Exercise of Series C preferred stock warrants (in shares)	287,446	1,653,004
Exercise of Series C preferred stock warrants	$ 1,754	$ 37,121
Conversion of preferred stock to common stock issued upon the conversion of preferred stock into common stock in IPO (in shares)		(23,178,555)
Conversion of preferred stock to common stock issued upon the conversion of preferred stock into common stock in IPO		$ (144,140)
Temporary equity, ending balance (in shares) at Jun. 30, 2019	0
Temporary equity, ending balance at Jun. 30, 2019	$ 0
Beginning balance (in shares) at Mar. 31, 2019			1,386,615
Beginning balance at Mar. 31, 2019	(158,074)		$ 1		5,194		(163,269)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock warrants (in shares)			3,764	2,204
Exercise of common stock warrants	31				31
Exercise of stock options (in shares)			176,576	6,000,000
Exercise of stock options	364	109,039	$ 1	$ 6	363	$ 109,033
Conversion of preferred stock to common stock issued upon the conversion of preferred stock into common stock in IPO (in shares)				23,178,555
Conversion of preferred stock to common stock issued upon the conversion of preferred stock into common stock in IPO		144,140		$ 23		144,117
Stock-based compensation	836				836
Net loss and comprehensive loss	(11,959)						(11,959)
Ending balance (in shares) at Jun. 30, 2019			30,747,714
Ending balance at Jun. 30, 2019	$ 84,377		$ 31		259,574		(175,228)
Temporary equity, ending balance (in shares) at Sep. 30, 2019	0
Temporary equity, ending balance at Sep. 30, 2019	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)			28,266
Exercise of stock options	68				68
Decrease in IPO offering costs	80				80
Stock-based compensation	925				925
Net loss	(8,007)
Net loss and comprehensive loss	(8,007)						(8,007)
Ending balance (in shares) at Sep. 30, 2019			30,775,980
Ending balance at Sep. 30, 2019	77,443		$ 31		260,647		(183,235)
Beginning balance (in shares) at Dec. 31, 2019			31,255,267
Beginning balance at Dec. 31, 2019	71,891		$ 31		263,384		(191,526)	$ 2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)			140,370
Exercise of stock options	274				274
Stock-based compensation	1,293				1,293
Net loss	(9,941)						(9,941)
Unrealized gain (loss) on investments, net	440							440
Ending balance (in shares) at Mar. 31, 2020			31,395,637
Ending balance at Mar. 31, 2020	63,957		$ 31		264,951		(201,467)	442
Beginning balance (in shares) at Dec. 31, 2019			31,255,267
Beginning balance at Dec. 31, 2019	$ 71,891		$ 31		263,384		(191,526)	2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	684,815
Net loss	$ (30,608)
Net loss and comprehensive loss	(30,458)
Ending balance (in shares) at Sep. 30, 2020			33,889,077
Ending balance at Sep. 30, 2020	119,738		$ 34		341,687		(222,135)	152
Beginning balance (in shares) at Mar. 31, 2020			31,395,637
Beginning balance at Mar. 31, 2020	63,957		$ 31		264,951		(201,467)	442
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)			265,467	1,923,076
Exercise of stock options	604	$ 70,543	$ 1	$ 2	603	$ 70,541
Issuance of common stock under employee stock purchase plan (in shares)			25,919
Issuance of common stock under employee stock purchase plan	801				801
Stock-based compensation	1,654				1,654
Net loss	(10,353)						(10,353)
Unrealized gain (loss) on investments, net	(126)							(126)
Ending balance (in shares) at Jun. 30, 2020			33,610,099
Ending balance at Jun. 30, 2020	127,080		$ 34		338,550		(211,820)	316
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)			278,978
Exercise of stock options	1,131				1,131
Stock-based compensation	2,006				2,006
Net loss	(10,315)						(10,315)
Net loss and comprehensive loss	(10,479)
Unrealized gain (loss) on investments, net	(164)							(164)
Ending balance (in shares) at Sep. 30, 2020			33,889,077
Ending balance at Sep. 30, 2020	$ 119,738		$ 34		$ 341,687		$ (222,135)	$ 152