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INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE (Details) (USD $) | 3 Months Ended | 8 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Sep. 30, 2013 | Jun. 30, 2013 | Mar. 31, 2013 | Sep. 30, 2012 | Sep. 30, 2012 | Sep. 30, 2013 | Sep. 30, 2012 | Dec. 31, 2012 | Jan. 24, 2012
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE |  |  |  |  |  |  |  |  |
Net loss | $ 3,264,000 |  |  | $ (2,654,000) |  | $ (136,399,000) | $ (40,369,000) |  |
Impairment |  |  |  |  |  | 95,878,000 |  |  |
Exploration properties in Santa Cruz, Argentina |  |  |  |  |  |  |  |  |
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE |  |  |  |  |  |  |  |  |
Tax on mining real estate property (as a percent) |  | 1.00% |  |  |  |  |  |  |
Reported |  |  |  |  |  |  |  |  |
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE |  |  |  |  |  |  |  |  |
Net loss |  |  |  | (2,583,000) |  |  | (40,578,000) |  |
Adjustment |  |  |  |  |  |  |  |  |
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE |  |  |  |  |  |  |  |  |
Net loss |  |  |  | (71,000) |  |  | 209,000 |  |
MSC |  |  |  |  |  |  |  |  |
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE |  |  |  |  |  |  |  |  |
Interest acquired (as a percent) | 49.00% |  |  |  |  | 49.00% |  |  |
Entity's share in earnings and losses from its investment in MSC | 2,658,000 |  |  | 12,908,000 | 18,505,000 | 3,914,000 |  | 25,301,000 |
Net income | 5,424,000 |  |  | 26,343,000 | 37,765,000 | 7,988,000 |  |  |
Interest held (as a percent) | 49.00% |  |  |  |  | 49.00% |  |  | 49.00%
Fair value of investment in MSC from acquisition of Minera Andes |  |  |  | 261,200,000 | 261,200,000 |  | 261,200,000 | 262,883,000 |
Amortization of fair value increments | 618,000 |  |  | 1,668,000 | 3,537,000 | 3,662,000 | 3,537,000 | 4,466,000 |
Equity method investment, overstatement of income from prior year recorded in current period |  |  | 3,900,000 |  |  |  |  |  |
Entity's share of income in investee, overstatement of income from prior year recorded in current period |  |  | 1,900,000 |  |  |  |  |  |
Impairment |  | 95,900,000 |  |  |  | 95,878,000 |  |  |
MSC | Exploration properties in Santa Cruz, Argentina |  |  |  |  |  |  |  |  |
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE |  |  |  |  |  |  |  |  |
Tax on mining real estate property (as a percent) |  | 1.00% |  |  |  |  |  |  |
MSC | Minimum | Exploration properties in Santa Cruz, Argentina |  |  |  |  |  |  |  |  |
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE |  |  |  |  |  |  |  |  |
Tax payable |  | 2,000,000 |  |  |  |  |  |  |
MSC | Maximum | Exploration properties in Santa Cruz, Argentina |  |  |  |  |  |  |  |  |
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE |  |  |  |  |  |  |  |  |
Tax payable |  | 3,000,000 |  |  |  |  |  |  |
MSC | Reported |  |  |  |  |  |  |  |  |
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE |  |  |  |  |  |  |  |  |
Amortization of fair value increments |  |  |  | 1,597,000 |  |  | 3,746,000 |  |
MSC | Adjustment |  |  |  |  |  |  |  |  |
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE |  |  |  |  |  |  |  |  |
Amortization of fair value increments |  |  |  | 71,000 |  |  | (209,000) |  |
MSC | Purchase price allocation adjustment |  |  |  |  |  |  |  |  |
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE |  |  |  |  |  |  |  |  |
Fair value of investment in MSC from acquisition of Minera Andes |  |  |  |  |  |  |  | $ 262,900,000 |

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