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SUPPLEMENTAL FINANCIAL INFORMATION - Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Revenue, Major Customer [Line Items] |  |  |
Revenue | $ 31,046 | $ 54,552 | $ 61,351
Deferred revenue | 2,474 | 2,339 |
Sales Revenue, Net | Customer Concentration Risk | Customer 1 |  |  |
Revenue, Major Customer [Line Items] |  |  |
Revenue | 13,080 | 33,360 | 20,980
Sales Revenue, Net | Customer Concentration Risk | Customer 2 |  |  |
Revenue, Major Customer [Line Items] |  |  |
Revenue | 6,990 | 8,690 | 16,310
Sales Revenue, Net | Customer Concentration Risk | Customer 3 |  |  |
Revenue, Major Customer [Line Items] |  |  |
Revenue | 4,400 | 7,000 | 12,530
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 | 20,070 | 50,760 | 37,850
Sales Revenue, Net | South Korea | Geographic Concentration Risk |  |  |
Revenue, Major Customer [Line Items] |  |  |
Revenue |  |  | 20,980
Sales Revenue, Net | Other | Geographic Concentration Risk |  |  |
Revenue, Major Customer [Line Items] |  |  |
Revenue | $ 4,400 | $ 3,690 | $ 1,870

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- Definition The noncurrent portion of deferred revenue amount as of balance sheet date. Deferred revenue is a liability related to a revenue producing activity for which revenue has not yet been recognized, and is not expected to be recognized in the next twelve months. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 8 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6935-107765 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 13.A.3(c).Q3) -URI http://asc.fasb.org/extlink&oid=65893310&loc=d3e214044-122780 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 13.A.4(a).Q1) -URI http://asc.fasb.org/extlink&oid=65893310&loc=d3e214044-122780 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 13.A.3(b)) -URI http://asc.fasb.org/extlink&oid=65893310&loc=d3e214044-122780 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 13.A.3(b).Q1(c)) -URI http://asc.fasb.org/extlink&oid=65893310&loc=d3e214044-122780 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 13.A.3) -URI http://asc.fasb.org/extlink&oid=65893310&loc=d3e214044-122780 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 13.A.3(b).Q2) -URI http://asc.fasb.org/extlink&oid=65893310&loc=d3e214044-122780 + Details
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