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SUPPLEMENTAL FINANCIAL INFORMATION - Narrative (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Revenue, Major Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue | $ 3,043 | $ 451 | $ 26,973 | $ 1,254 | $ 3,908 | $ 5,499 | $ 17,883 | $ 3,756 | $ 31,721 | $ 31,046 | $ 54,552
Deferred revenue | $ 2,724 |  |  |  | $ 2,474 |  |  |  | 2,724 | 2,474 |
Sales Revenue, Net | Customer Concentration Risk | Customer 1 |  |  |  |  |  |  |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 24,520 | 13,080 | 33,360
Sales Revenue, Net | Customer Concentration Risk | Customer 2 |  |  |  |  |  |  |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 5,030 | 6,990 | 8,690
Sales Revenue, Net | Customer Concentration Risk | Customer 3 |  |  |  |  |  |  |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 1,240 | 4,400 | 7,000
Sales Revenue, Net | United States | Geographic Concentration Risk |  |  |  |  |  |  |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 25,760 | 20,070 | 50,760
Sales Revenue, Net | Other | Geographic Concentration Risk |  |  |  |  |  |  |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | $ 5,030 | $ 4,400 | $ 3,690

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