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INCOME TAXES - Changes to valuation allowance (Details) - USD ($) $ in Thousands |  | 12 Months Ended
--- | --- | ---
Jan. 01, 2014 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Valuation allowance |  |  |  |
Change in valuation allowance |  | $ 7,000 | $ 4,600 |
Balance at Beginning of Period | $ 125,202 | 129,794 | 125,202 | $ 90,477
Additions |  | 6,873 | 11,514 | 35,547
Deductions |  | (13,899) | (6,922) | (822)
Balance at End of Period |  | $ 122,768 | $ 129,794 | $ 125,202
Special mining duty (as a percent) |  | 7.50% |  |
Mexico |  |  |  |
Valuation allowance |  |  |  |
Deductions related to development type costs | $ 0 |  |  |
Special mining duty (as a percent) | 7.50% |  |  |

X
- Definition Represents the amount of deductions related to development type costs. + References No definition available. + Details
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- Definition Represents the percentage of special mining duty. + References No definition available. + Details
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- Definition Amount of decrease in the valuation allowance for a specified deferred tax asset. + References No definition available. + Details
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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=6907707&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=37586315&loc=d3e32123-109318 + Details
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