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Note 4 - Environmental and Reclamation Activities - Accrued Reclamation and Closure Cost Liability Activity (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Balance | $ 85,580 | $ 95,538 | $ 57,250
Accruals for estimated costs | 16 | 705 | 15,114
Accretion expense | 4,870 | 3,158 | 1,904
Revision of estimated cash flows due to changes in reclamation plans | (578) | 2,759 | 4,112
Addition due to development and production at our San Sebastian unit |  |  | 1,189
Payment of reclamation obligations | (3,843) | (17,704) | (1,544)
Balance | $ 86,045 | 85,580 | 95,538
Revett Mining Company, Inc. [Member] |  |  |
Liability addition due to acquisition of Revett |  |  | $ 17,513
Mines Management [Member] |  |  |
Liability addition due to acquisition of Revett |  | $ 1,124 |

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