CONDENSED CONSOLIDATED STATEMENT OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (Unaudited) - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Series C-2 Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Related Party Promissory Notes for the Purchase of Common Stock	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2018		$ 161,111
Beginning balance, shares at Dec. 31, 2018		98,491,880
Beginning balance at Dec. 31, 2018	$ (97,113)			$ 1	$ 22,441	$ (598)	$ (118,953)	$ (4)
Beginning balance, shares at Dec. 31, 2018				878,413
Issuance of convertible preferred stock, net of issuance cost			$ 6,947
Issuance of convertible preferred stock, net of issuance cost, shares			3,039,908
Issuance of common stock upon exercise of stock options, net of repurchase	66				66
Issuance of common stock upon exercise of stock options, net of repurchase, shares				3,685
Repurchase of common stock from related party	109					109
Repurchase of common stock from related party, shares				(53,649)
Interest on promissory notes from related parties for purchase of common stock	(2)					(2)
Stock-based compensation	377				377
Net loss	(9,188)						(9,188)
Ending balance at Mar. 31, 2019		$ 168,058
Ending balance, shares at Mar. 31, 2019		101,531,788
Ending balance at Mar. 31, 2019	(105,751)			$ 1	22,884	(491)	(128,141)	(4)
Ending balance, shares at Mar. 31, 2019				828,449
Beginning balance at Dec. 31, 2018		$ 161,111
Beginning balance, shares at Dec. 31, 2018		98,491,880
Beginning balance at Dec. 31, 2018	(97,113)			$ 1	22,441	(598)	(118,953)	(4)
Beginning balance, shares at Dec. 31, 2018				878,413
Foreign currency translation adjustment	17
Net loss	(29,781)
Ending balance at Sep. 30, 2019		$ 175,490
Ending balance, shares at Sep. 30, 2019		104,803,325
Ending balance at Sep. 30, 2019	(124,797)			$ 1	23,923		(148,734)	13
Ending balance, shares at Sep. 30, 2019				935,040
Beginning balance at Mar. 31, 2019		$ 168,058
Beginning balance, shares at Mar. 31, 2019		101,531,788
Beginning balance at Mar. 31, 2019	(105,751)			$ 1	22,884	(491)	(128,141)	(4)
Beginning balance, shares at Mar. 31, 2019				828,449
Issuance of convertible preferred stock, net of issuance cost			$ 7,451
Issuance of convertible preferred stock, net of issuance cost, shares			3,271,537
Issuance of common stock upon exercise of stock options, net of repurchase	34				34
Issuance of common stock upon exercise of stock options, net of repurchase, shares				13,996
Repurchase of common stock from related party	65					65
Repurchase of common stock from related party, shares				29,686
Paydown of promissory notes from related parties for purchase of common stock	73					73
Forgiveness of promissory notes from related parties for purchase of common stock	353					$ 353
Stock-based compensation	347				347
Foreign currency translation adjustment	2							2
Net loss	(10,622)						(10,622)
Ending balance at Jun. 30, 2019		$ 175,509
Ending balance, shares at Jun. 30, 2019		104,803,325
Ending balance at Jun. 30, 2019	(115,499)			$ 1	23,265		(138,763)	(2)
Ending balance, shares at Jun. 30, 2019				812,759
Issuance cost related to convertible preferred stock			$ (19)
Issuance of common stock upon exercise of stock options, net of repurchase	227				227
Issuance of common stock upon exercise of stock options, net of repurchase, shares				122,281
Stock-based compensation	431				431
Foreign currency translation adjustment	15							15
Net loss	(9,971)						(9,971)
Ending balance at Sep. 30, 2019		$ 175,490
Ending balance, shares at Sep. 30, 2019		104,803,325
Ending balance at Sep. 30, 2019	(124,797)			$ 1	23,923		(148,734)	13
Ending balance, shares at Sep. 30, 2019				935,040
Beginning balance at Dec. 31, 2019	$ 73,121			$ 2	235,049		(161,950)	20
Beginning balance, shares at Dec. 31, 2019	21,833,037			21,833,037
Issuance of common stock, net of issuance costs	$ 69,842				69,842
Issuance of common stock, net of issuance costs, shares				2,500,000
Issuance of common stock upon exercise of stock options, net of repurchase	30				30
Issuance of common stock upon exercise of stock options, net of repurchase, shares				970
Stock-based compensation	2,088				2,088
Foreign currency translation adjustment	204							204
Unrealized gain (loss) on marketable securities	(217)							(217)
Net loss	(13,139)						(13,139)
Ending balance at Mar. 31, 2020	131,929			$ 2	307,009		(175,089)	7
Ending balance, shares at Mar. 31, 2020				24,334,007
Beginning balance at Dec. 31, 2019	$ 73,121			$ 2	235,049		(161,950)	20
Beginning balance, shares at Dec. 31, 2019	21,833,037			21,833,037
Foreign currency translation adjustment	$ (65)
Unrealized gain (loss) on marketable securities	119
Net loss	(40,157)
Ending balance at Sep. 30, 2020	$ 110,047			$ 2	312,078		(202,107)	74
Ending balance, shares at Sep. 30, 2020	24,495,525			24,495,525
Beginning balance at Mar. 31, 2020	$ 131,929			$ 2	307,009		(175,089)	7
Beginning balance, shares at Mar. 31, 2020				24,334,007
Issuance of common stock upon exercise of stock options, net of repurchase	453				453
Issuance of common stock upon exercise of stock options, net of repurchase, shares				68,485
Stock-based compensation	2,035				2,035
Issuance of common stock under the employee stock purchase plan	411				411
Issuance of common stock under the employee stock purchase plan, shares				40,350
Foreign currency translation adjustment	(199)							(199)
Unrealized gain (loss) on marketable securities	369							369
Net loss	(12,387)						(12,387)
Ending balance at Jun. 30, 2020	122,611			$ 2	309,908		(187,476)	177
Ending balance, shares at Jun. 30, 2020				24,442,842
Issuance of common stock upon exercise of stock options, net of repurchase	165				165
Issuance of common stock upon exercise of stock options, net of repurchase, shares				52,683
Stock-based compensation	2,005				2,005
Foreign currency translation adjustment	(70)							(70)
Unrealized gain (loss) on marketable securities	(33)							(33)
Net loss	(14,631)						(14,631)
Ending balance at Sep. 30, 2020	$ 110,047			$ 2	$ 312,078		$ (202,107)	$ 74
Ending balance, shares at Sep. 30, 2020	24,495,525			24,495,525