INCOME TAXES - DEFERRED TAXES (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Significant components of deferred tax assets
Net operating loss carryforwards	$ 241,300,000	$ 217,100,000
Federal and state tax credits	49,600,000	42,800,000
Capitalized research and development	6,900,000	6,000,000
Stock-based compensation	10,200,000	9,400,000
Operating lease liabilities	1,400,000	1,200,000
Other	2,600,000	2,100,000
Total deferred tax assets	312,000,000	278,600,000
Less: valuation allowance	(310,700,000)	(277,200,000)
Net deferred tax assets	1,300,000	1,400,000
Operating leases, right-of-use assets	(1,300,000)	(1,400,000)
Total deferred tax liabilities	(1,300,000)	(1,400,000)
Valuation allowance
Increase (decrease) in valuation allowance	$ 33,500,000	$ 19,300,000