INCOME TAXES - Significant Components of Deferred Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets (liabilities):
Net operating loss carryforward	$ 100,346	$ 94,132
Stock compensation	3,541	3,539
Intangible assets	7,156	7,682
Research and development credit	18,076	17,787
Operating lease assets	0	(213)
Operating lease liabilities	0	354
Other	(144)
Other		976
Total deferred tax assets, net of deferred tax liabilities	128,975	124,257
Valuation allowance	(128,975)	(124,257)
Net deferred tax	$ 0	$ 0