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SUPPLEMENTAL FINANCIAL INFORMATION - Narrative (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Revenue, Major Customer [Line Items] |  |  |  |  |
Revenue | $ 54,552 | $ 61,351 | $ 54,552 | $ 61,351 | $ 46,253
Deferred revenue | $ 2,339 | $ 2,165 | 2,339 | 2,165 |
Sales Revenue, Net | Customer Concentration Risk | Customer 1 |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |
Revenue |  |  | 33,360 | 20,980 | 20,660
Sales Revenue, Net | Customer Concentration Risk | Customer 2 |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |
Revenue |  |  | 8,690 | 16,310 | 8,570
Sales Revenue, Net | Customer Concentration Risk | Customer 3 |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |
Revenue |  |  | 7,000 | 12,530 | 16,530
Sales Revenue, Net | Customer Concentration Risk | Customer 4 |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |
Revenue |  |  |  | 9,000 |
Sales Revenue, Net | United States | Geographic Concentration Risk |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |
Revenue |  |  | 50,760 | 37,850 | 25,590
Sales Revenue, Net | South Korea | Geographic Concentration Risk |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |
Revenue |  |  |  | 20,980 | $ 20,660
Sales Revenue, Net | Other | Geographic Concentration Risk |  |  |  |  |
Revenue, Major Customer [Line Items] |  |  |  |  |
Revenue |  |  | $ 3,690 | $ 1,870 |

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