Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Total	Series Seed Redeemable Convertible Preferred Stock [Member]	Series A Redeemable Convertible Preferred Stock [Member]	Series B Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
Begining balance at Dec. 31, 2016	$ (4,579)	$ 1,500	$ 7,500			$ 247	$ (4,826)
Begining balance, shares at Dec. 31, 2016		3,333,333	5,714,286		2,172,068
Issuance of series A redeemable convertible preferred stock dividend	0	$ 0	$ 0	$ 0	$ 0	0	0
Issuance of series A redeemable convertible preferred stock dividend, shares			3,720,864
Issuance of redeemable convertible preferred stock,			$ 17,415
Issuance of redeemable convertible preferred stock, shares			22,015,349
Vesting of restricted stock awards	0	0	$ 0	0	$ 0	0	0
Vesting of restricted stock awards, shares					133,105
Stock-based compensation expense	109					177
Accretion of issuance costs related to redeemable convertible preferred stock	(85)		85			(85)
Net loss	(18,648)						(18,648)
Ending balance at Dec. 31, 2017	(23,135)	$ 1,500	$ 25,000			339	(23,474)
Ending 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
Vesting of restricted stock awards	0	$ 0	$ 0	$ 0	$ 0	0	0
Issuance of series B redeemable convertible preferred stock to settle accrued liability of license cost				$ 500
Vesting of restricted stock awards, shares					123,026
Issuance of series B redeemable convertible preferred stock to settle accrued liability of license cost, shares				233,765
Stock-based compensation expense	2,196					2,196
Accretion of issuance costs related to redeemable convertible preferred stock	(2,243)			$ 2,243		(339)	(1,904)
Issuance of common stock upon IPO	104,013				$ 1	104,012
Issuance of common stock upon IPO, shares					6,035,151
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	0	$ 0	$ 0	$ 0	$ 0	0	0
Exercise of warrants to purchase common stock, shares					6,091
Exercise of stock options	$ 17					17
Exercise of stock options, shares	16,974				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