Condensed Statements of Redeemable Convertible Preferred Stock And Stockholders' Deficit - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Series A Redeemable Convertible Preferred Stock [Member]	Series A Redeemable Convertible Preferred Stock [Member] Preferred Stock [Member]	Series B Redeemable Convertible Preferred Stock [Member]	Series B Redeemable Convertible Preferred Stock [Member] Preferred Stock [Member]	Series C Redeemable Convertible Preferred Stock [Member]	Series C Redeemable Convertible Preferred Stock [Member] Preferred Stock [Member]
Beginning balance at Dec. 31, 2018							$ 30,482		$ 41,491
Beginning balance, shares at Dec. 31, 2018							25,000,000		17,522,259
Beginning balance at Dec. 31, 2018	$ (62,801)		$ 1		$ (62,802)
Beginning balance, shares at Dec. 31, 2018			1,394,961
Issuance of series redeemable convertible preferred, shares									5,072,232
Issuance of series redeemable convertible preferred									$ 10,949
Accretion of issuance costs related to redeemable convertible preferred stock	(51)				(51)				51
Exercise of stock options	74			$ 74
Exercise of stock options, shares			77,876
Exercise of series B preferred stock tranche right	0
Vesting of restricted stock awards, shares			10,276
Stock-based compensation expense	157			157
Accrued dividends on redeemable convertible preferred stock	(2,728)			(231)	(2,497)		$ 992		1,736
Net loss	(14,090)				(14,090)
Ending balance at Jun. 30, 2019							$ 31,474		$ 54,227
Ending balance, shares at Jun. 30, 2019							25,000,000		22,594,491
Ending balance at Jun. 30, 2019	(79,439)		$ 1		(79,440)
Ending balance, shares at Jun. 30, 2019			1,483,113
Beginning balance at Mar. 31, 2019							$ 30,975		$ 53,250
Beginning balance, shares at Mar. 31, 2019							25,000,000		22,594,491
Beginning balance at Mar. 31, 2019	(71,185)		$ 1		(71,186)
Beginning balance, shares at Mar. 31, 2019			1,400,099
Issuance of series redeemable convertible preferred									$ 33
Conversion of convertible loan notes into redeemable preferred stock									(33)
Accretion of issuance costs related to redeemable convertible preferred stock	(33)				(33)
Exercise of stock options	74			74
Exercise of stock options, shares			77,876
Vesting of restricted stock awards, shares			5,138
Stock-based compensation expense	78			78
Accrued dividends on redeemable convertible preferred stock	(1,476)			(152)	(1,324)		$ 499		977
Net loss	(6,897)				(6,897)
Ending balance at Jun. 30, 2019							$ 31,474		$ 54,227
Ending balance, shares at Jun. 30, 2019							25,000,000		22,594,491
Ending balance at Jun. 30, 2019	(79,439)		$ 1		(79,440)
Ending balance, shares at Jun. 30, 2019			1,483,113
Beginning balance at Dec. 31, 2019	$ 96,928					$ 32,482	$ 32,482	$ 64,446	$ 64,446
Beginning balance, shares at Dec. 31, 2019	51,283,386					25,000,000	25,000,000	26,283,386	26,283,386
Beginning balance at Dec. 31, 2019	$ (97,436)		$ 1		(97,437)
Beginning balance, shares at Dec. 31, 2019			1,488,489
Issuance of series redeemable convertible preferred, shares									3,688,898		46,828,167
Issuance of series redeemable convertible preferred									$ 7,973		$ 74,571
Conversion of convertible loan notes into redeemable preferred stock											$ 10,083
Conversion of convertible loan notes into redeemable preferred stock, shares											6,295,756
Accretion of issuance costs related to redeemable convertible preferred stock	$ (456)				(456)				27		$ 429
Exercise of stock options, shares	0
Exercise of series B preferred stock tranche right	$ 300								300
Stock-based compensation expense	201			201
Accrued dividends on redeemable convertible preferred stock	(3,957)			(201)	(3,756)		$ 997		2,568		392
Net loss	(16,149)				(16,149)
Ending balance at Jun. 30, 2020	$ 194,268					$ 33,479	$ 33,479	$ 75,314	$ 75,314	$ 85,475	$ 85,475
Ending balance, shares at Jun. 30, 2020	108,096,207	53,123,923				25,000,000	25,000,000	29,972,284	29,972,284	53,123,923	53,123,923
Ending balance at Jun. 30, 2020	$ (117,797)		$ 1		(117,798)
Ending balance, shares at Jun. 30, 2020			1,488,489
Beginning balance at Mar. 31, 2020							$ 32,980		$ 74,018
Beginning balance, shares at Mar. 31, 2020							25,000,000		29,972,284
Beginning balance at Mar. 31, 2020	(106,933)		$ 1		(106,934)
Beginning balance, shares at Mar. 31, 2020			1,488,489
Issuance of series redeemable convertible preferred, shares											46,828,167
Issuance of series redeemable convertible preferred											$ 74,571
Conversion of convertible loan notes into redeemable preferred stock											$ 10,083
Conversion of convertible loan notes into redeemable preferred stock, shares											6,295,756
Accretion of issuance costs related to redeemable convertible preferred stock	(429)				(429)						$ 429
Stock-based compensation expense	100			100
Accrued dividends on redeemable convertible preferred stock	(2,187)			$ (100)	(2,087)		$ 499		$ 1,296		392
Net loss	(8,348)				(8,348)
Ending balance at Jun. 30, 2020	$ 194,268					$ 33,479	$ 33,479	$ 75,314	$ 75,314	$ 85,475	$ 85,475
Ending balance, shares at Jun. 30, 2020	108,096,207	53,123,923				25,000,000	25,000,000	29,972,284	29,972,284	53,123,923	53,123,923
Ending balance at Jun. 30, 2020	$ (117,797)		$ 1		$ (117,798)
Ending balance, shares at Jun. 30, 2020			1,488,489