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INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE (Details) (USD $) | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended | 3 Months Ended
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Sep. 30, 2014 | Sep. 30, 2013 | Sep. 30, 2014 | Sep. 30, 2013 | Sep. 30, 2014 MSC | Sep. 30, 2013 MSC | Jun. 30, 2013 MSC | Mar. 31, 2013 MSC | Sep. 30, 2014 MSC | Sep. 30, 2013 MSC | Dec. 31, 2013 MSC | Dec. 31, 2013 MSC Exploration properties in Santa Cruz, Argentina Vend-in agreement
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  | 49.00% | 49.00% |  |  | 49.00% | 49.00% |  |
Income (loss) on investment in Minera Santa Cruz S.A. (net of amortization) | $ (4,441,000) | $ 2,040,000 | $ 150,000 | $ 252,000 | $ (4,441,000) | $ 2,040,000 |  |  | $ 150,000 | $ 252,000 |  |
Equity method investment, overstatement of income from prior year recorded in current period |  |  |  |  |  |  |  | 3,900,000 |  |  |  |
Entity's share of income in investee, understatement of income from prior year recorded in current period |  |  |  |  |  |  |  |  |  | 1,900,000 |  |
Impairment of investment in MSC |  |  |  | 95,878,000 |  |  | 95,900,000 |  |  | 95,900,000 | 95,878,000 |
Carrying value of properties, net of tax |  |  |  |  |  |  |  |  |  |  | 35,857,000 | 35,900,000
Deferred tax liability related to mineral properties transferred |  |  |  |  |  |  |  |  |  |  |  | 17,300,000
(Gain) loss on sale of assets | (8,000) | (50,000) | (26,000) | 6,741,000 |  |  |  |  |  |  |  | 0
Dividends received |  |  | $ 9,483,000 | $ 1,242,000 | $ 2,400,000 | $ 1,200,000 |  |  | $ 9,500,000 | $ 1,200,000 |  |

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