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INCOME AND MINING TAXES - Tax Effects of Temporary Differences (Details) - USD ($) $ in Thousands | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Deferred tax assets: |  |  |  |
Net operating loss carryforward | $ 57,667 | $ 55,515 |  |
Mineral properties | 60,299 | 62,345 |  |
Other temporary differences | 14,356 | 15,198 |  |
Total gross deferred tax assets | 132,322 | 133,058 |  |
Less: valuation allowance | (121,212) | (124,153) | $ (123,648) | $ (111,621)
Net deferred tax assets | 11,110 | 8,905 |  |
Deferred tax liabilities: |  |  |  |
Acquired mineral property interests | (16,024) | (15,331) |  |
Total deferred tax liabilities | (16,024) | (15,331) |  |
Total net deferred tax liability | (4,914) | $ (6,426) |  |
Valuation allowances | $ 2,900 |  |  |

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