CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended						6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2023	Dec. 31, 2022
Total revenue	$ 3,699	$ 485	$ 443	$ 466	$ 643	$ 500	$ 928	$ 1,143	$ 4,627	$ 1,609	$ 6,036	$ 2,488
Operating expenses
Research and development	7,048	14,574	10,172	17,937	11,602	9,393	24,746	20,995	31,794	38,932	39,573	56,159
General and administrative	9,082	9,451	8,306	7,639	10,617	10,137	17,757	20,754	26,839	28,393	31,994	35,400
Total operating expenses	16,130	24,025	18,478	25,576	22,219	19,530	42,503	41,749	58,633	67,325	71,567	91,559
Loss from operations	(12,431)	(23,540)	(18,035)	(25,110)	(21,576)	(19,030)	(41,575)	(40,606)	(54,006)	(65,716)	(65,531)	(89,071)
Other income (expense), net	714	475	709	1,197	94	15	1,184	109	1,898	1,306	2,453	2,267
Net loss	(11,717)	(23,065)	(17,326)	(23,913)	(21,482)	(19,015)	(40,391)	(40,497)	(52,108)	(64,410)	(63,078)	(86,804)
Other comprehensive income (loss)
Foreign currency translation adjustment	5	(2)	(1)	20	10	0	(3)	10	2	30	(5)	25
Unrealized gain (loss) on marketable securities	0	(1)		0	0		(1)	0	(1)	0	(1)	1
Comprehensive loss	$ (11,712)	$ (23,068)	$ (17,327)	$ (23,893)	$ (21,472)	$ (19,015)	$ (40,395)	$ (40,487)	$ (52,107)	$ (64,380)	$ (63,084)	$ (86,778)
Shares used in calculating net loss per common share - basic (in shares)	256,492,558	238,311,498	225,523,627	216,591,011	215,862,977	205,693,498	231,952,888	210,806,330	240,222,667	212,755,746	244,327,057	214,600,051
Shares used in calculating net loss per common share - diluted (in shares)	256,492,558	238,311,498	225,523,627	216,591,011	215,862,977	205,693,498	231,952,888	210,806,330	240,222,667	212,755,746	244,327,057	214,600,051
Net loss per share of common stock - basic (in USD per share)	$ (0.05)	$ (0.10)	$ (0.08)	$ (0.11)	$ (0.10)	$ (0.09)	$ (0.17)	$ (0.19)	$ (0.22)	$ (0.30)	$ (0.26)	$ (0.40)
Net loss per share of common stock - diluted (in USD per share)	$ (0.05)	$ (0.10)	$ (0.08)	$ (0.11)	$ (0.10)	$ (0.09)	$ (0.17)	$ (0.19)	$ (0.22)	$ (0.30)	$ (0.26)	$ (0.40)
Collaborative arrangement revenue
Total revenue	$ 3,699	$ 485	$ 443	$ 466	$ 643	$ 500	$ 928	$ 1,143	$ 4,627	$ 1,609	$ 6,036	$ 2,488
Operating expenses
Research and development											$ 5,300	$ 9,100