Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Total	IPO [Member]	Series Seed Redeemable Convertible Preferred Stock [Member]	Series A Redeemable Convertible Preferred Stock [Member]	Series B Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member] IPO [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] IPO [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2017	$ (23,135)		$ 1,500	$ 25,000				$ 339		$ (23,474)
Beginning balance, shares at Dec. 31, 2017			3,333,333	31,450,499		2,305,173
Issuance of redeemable convertible preferred stock,					$ 58,257
Issuance of redeemable convertible preferred stock, shares					28,285,557
Issuance of series B redeemable convertible preferred stock to settle accrued liability of license cost					$ 500
Issuance of series B redeemable convertible preferred stock to settle accrued liability of license cost, shares					233,765
Accretion of issuance costs related to redeemable convertible preferred stock	(2,243)				$ 2,243			(339)		(1,904)
Issuance of common stock upon IPO/public offering, net of issuance/offering costs		$ 104,013					$ 1		$ 104,012
Issuance of common stock upon IPO/public offering, net of issuance/offering costs, shares							6,035,151
Stock-based compensation expense	2,196							2,196
Reclassification of warrants to purchase redeemable convertible stock into warrants to purchase common stock	197							197
Conversion of redeemable convertible preferred stock into common stock	87,500		$ (1,500)	$ (25,000)	$ (61,000)	$ 1		87,499
Conversion of redeemable convertible preferred stock into common stock, shares			(3,333,333)	(31,450,499)	(28,519,322)	15,320,213
Exercise of warrants to purchase common stock, shares						6,091
Vesting of restricted stock awards, shares						123,026
Exercise of stock options	17							17
Exercise of stock options, shares						16,974
Net loss	(46,361)									(46,361)
Ending balance at Dec. 31, 2018	122,184					$ 2		193,921		(71,739)
Ending balance, shares at Dec. 31, 2018						23,806,628
Issuance of common stock upon IPO/public offering, net of issuance/offering costs		$ 129,465					$ 1		$ 129,464
Issuance of common stock upon IPO/public offering, net of issuance/offering costs, shares							7,475,000
Issuance of common stock under 2018 employee stock purchase plan	27							27
Issuance of common stock under 2018 employee stock purchase plan, shares						1,671
Stock-based compensation expense	6,800							6,800
Vesting of restricted stock awards, shares						123,024
Exercise of stock options	$ 502							502
Exercise of stock options, shares	236,483					236,483
Net loss	$ (72,965)									(72,965)
Ending balance at Dec. 31, 2019	$ 186,013					$ 3		$ 330,714		$ (144,704)
Ending balance, shares at Dec. 31, 2019						31,642,806