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INCOME TAXES - Tax credit carry forwards (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
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California Enterprise Zone tax credits |  |
Tax Credit Carryforward [Line Items] |  |
Tax credit carry forwards | $ 0.1 | $ 0.1
Federal | Research and development tax credit |  |
Tax Credit Carryforward [Line Items] |  |
Tax credit carry forwards | 0.7 | 1.0
State | Research and development tax credit |  |
Tax Credit Carryforward [Line Items] |  |
Tax credit carry forwards | $ 0.7 | $ 1.0

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- Definition The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319 + Details
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