CONSOLIDATED STATEMENTS OF CHANGES IN REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Redeemable Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (loss)	Accumulated Deficit
Balance at Dec. 31, 2017	$ (76,105)				$ (3)	$ (76,102)
Balance (in shares) at Dec. 31, 2017		64,689,359
Balance at Dec. 31, 2017		$ 90,148
Balance (in shares) at Dec. 31, 2017			300,597
Sale of Series C redeemable convertible preferred stock, net of issuance costs of $0.3 million		$ 69,844
Sale of Series C redeemable convertible preferred stock,net of issuance costs, shares		31,696,436
Share-based compensation expense	865			$ 865
Accretion of redeemable convertible preferred stock to redemption value	(5,910)	$ 5,910		(865)		(5,045)
Unrealized gain on short-term investments	6				6
Net loss	(23,676)					(23,676)
Balance at Dec. 31, 2018	$ (104,820)				3	(104,823)
Balance (in shares) at Dec. 31, 2018	96,385,795	96,385,795
Balance at Dec. 31, 2018	$ 165,902	$ 165,902
Balance (in shares) at Dec. 31, 2018	300,597		300,597
Share-based compensation expense	$ 2,390			2,390
Accretion of redeemable convertible preferred stock to redemption value	(7,178)	7,178		(2,581)		(4,597)
Conversion of redeemable convertible preferred stock into common stock	173,080	$ (173,080)	$ 19	173,061
Conversion of redeemable convertible preferred stock into common stock, shares		(96,385,795)	19,061,502
Sale of common stock in initial public offering, net of issuance costs of $7.3 million	58,021		$ 6	58,015
Sale of common stock in initial public offering, net of issuance costs, shares			5,445,690
Exercise of stock options	$ 10			10
Exercise of stock options, shares	3,778		3,778
Unrealized gain on short-term investments	$ 35				35
Net loss	(51,930)					(51,930)
Balance at Dec. 31, 2019	$ 69,608		$ 25	$ 230,895	$ 38	$ (161,350)
Balance (in shares) at Dec. 31, 2019	24,811,567		24,811,567