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INCOME AND MINING TAXES - Changes to Valuation Allowance (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Valuation allowance |  |  |
Balance at Beginning of Period | $ 111,621 | $ 122,768 | $ 129,794
Additions | 51,220 | 1,430 | 6,873
Deductions | (39,193) | (12,577) | (13,899)
Balance at End of Period | 123,648 | $ 111,621 | $ 122,768
Black Fox |  |  |
Valuation allowance |  |  |
Change in valuation allowance | $ 12,000 |  |

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- Definition Amount of increase in the valuation allowance for a specified deferred tax asset. + References No definition available. + Details
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- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
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- Definition Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=84176650&loc=d3e32123-109318 + Details
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