INCOME TAXES - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
NOL carryforwards	$ 66,374	$ 63,381	$ 57,935
R&D credit carryforwards	4,489	4,316	3,787
IRC 174 Capitalized R&D	6,214	0	0
Accruals and other	5,326	4,058	3,811
Capitalized start-up costs	34	53	70
Other	16	41	28
Gross deferred tax assets	82,453	71,849	65,631
Deferred tax liabilities:
IPR&D	0	(3,969)	(12,528)
Gross deferred tax liabilities	0	(3,969)	(12,528)
Valuation allowance	(82,453)	(71,849)	(65,631)
Net Deferred Tax Liability	$ 0	$ (3,969)	$ (12,528)