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SUPPLEMENTAL FINANCIAL INFORMATION - Narrative (Details) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Revenue, Major Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue | $ 384,000 | $ 486,000 | $ 395,000 | $ 393,000 | $ 701,000 | $ 423,000 | $ 3,071,000 | $ 1,670,000 | $ 1,658,000 | $ 5,865,000 | $ 31,721,000
Contract with Customer, Liability | $ 0 |  |  |  | $ 0 |  |  |  | 0 | 0 | 2,720,000
Sales Revenue, Net | Customer Concentration Risk | Customer 1 |  |  |  |  |  |  |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 1,550,000 | 2,720,000 | 24,520,000
Sales Revenue, Net | Customer Concentration Risk | Customer 2 |  |  |  |  |  |  |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  | 770,000 | 5,030,000.00
Sales Revenue, Net | Customer Concentration Risk | Customer 3 |  |  |  |  |  |  |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  | 750,000 | 1,240,000
Sales Revenue, Net | Customer Concentration Risk | Customer 4 |  |  |  |  |  |  |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  | 740,000 |
Sales Revenue, Net | United States | Geographic Concentration Risk |  |  |  |  |  |  |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | $ 1,660,000 | 5,800,000 | 25,760,000
Sales Revenue, Net | Other | Geographic Concentration Risk |  |  |  |  |  |  |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  | $ 70,000.00 | $ 5,030,000.00

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