INCOME TAXES - Net deferred tax assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Significant components of net deferred tax asset
Net operating loss carryforward	$ 44,249	$ 42,696
Research and development credit carryforward	1,718	1,663
Stock-based compensation	359	431
Depreciation and amortization	4	17
Capitalized research expenses	1,226
Accrued expenses	189
Lease liability	252	344
Right of use asset	(224)	(323)
Other deferred tax liabilities	(225)
Accruals and other temporary differences	189
Subtotal	47,548	44,828
Valuation allowance	(47,548)	(44,828)
Net deferred taxes	0	0
Retained earnings	(248,619)	(238,129)
Increase (decrease) in valuation allowance	2,700	2,600
Uncertain tax positions that would affect its effective tax rate	0	$ 0
Amount of significant change in uncertain tax positions over the next 12 months	$ 0