INCOME TAXES - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
U.S. Federal and State
U.S. federal and state deferred tax assets—long term:
Accrued payroll	$ 200	$ 180
Accrued expenses	54	53
Fixed assets	36	17
Charitable contributions	28	14
Intangibles	473	431
Research & development credit	4,874	3,830
Net operating loss	44,772	35,279
Stock compensation	658	519
Lease liabilities	499	700
New jobs credit	8	8
Total deferred tax assets	51,602	41,031
U.S. federal and state deferred tax liabilities—long term:
Right of use assets	(432)	(621)
Total deferred tax liabilities	(432)	(621)
Total long-term assets	51,170	40,410
Less: Valuation allowance	(51,170)	(40,410)
Net deferred tax assets	0	0
Foreign
U.S. federal and state deferred tax assets—long term:
Net operating loss	8	6
U.S. federal and state deferred tax liabilities—long term:
Total long-term assets	8	6
Less: Valuation allowance	(8)	(6)
Net deferred tax assets	$ 0	$ 0