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INCOME TAXES - DEFERRED TAXES (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Significant components of deferred tax assets |  |
Net operating loss carryforwards | $ 217,100,000 | $ 204,600,000
Federal and state tax credits | 42,800,000 | 38,400,000
Capitalized research and development | 6,000,000 | 5,900,000
Stock-based compensation | 9,400,000 | 7,700,000
Operating lease liabilities | 1,200,000 | 700,000
Other | 2,100,000 | 1,200,000
Total deferred tax assets | 278,600,000 | 258,500,000
Less: valuation allowance | (277,200,000) | (257,900,000)
Net deferred tax assets | 1,400,000 | 600,000
Operating leases, right-of-use assets | (1,400,000) | (600,000)
Total deferred tax liabilities | (1,400,000) | (600,000)
Valuation allowance |  |
Increase (decrease) in valuation allowance | $ 19,300,000 | $ 20,800,000

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