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SUPPLEMENTAL FINANCIAL INFORMATION - Schedule of Other Nonoperating Income (Expense) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract] |  |  |
Interest income | $ 153 | $ 482 | $ 336
Change in value of investments accounted for at fair value | 1,835 | (153) | 769
Change in value of warrant liabilities | (5,436) | 3,726 | (3,469)
Change in value of Convertible Debentures | 155 | 291 | (612)
Foreign exchange gain (loss) | 767 | (46) | 0
Sales and property tax refunds | 0 | 0 | 341
Sale of surplus assets | 0 | 0 | 293
Other | 233 | (322) | 14
Other income (loss) | $ (2,293) | $ 3,978 | $ (2,328)

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