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Asset Impairment Review (Narrative) (Details) - USD ($) $ in Thousands | 1 Months Ended | 12 Months Ended
--- | --- | ---
Oct. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017
Impairment Effects on Earnings Per Share [Line Items] |  |  |
Proceeds from Bulldog property |  |  | $ 4,940
Carlisle Assets [Member] |  |  |
Impairment Effects on Earnings Per Share [Line Items] |  |  |
Mine carrying value |  | $ 107,000 |
Asset impairment |  | $ 0 |
Bulldog Mine [Member] |  |  |
Impairment Effects on Earnings Per Share [Line Items] |  |  |
Proceeds from Bulldog property | $ 4,900 |  |
Period of rights to repurchase the property |  | 8 years |
Assets with repurchase agreement aggregate net carrying value |  | $ 15,000 |

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- Definition Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2420-110228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 + Details
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- Definition Carrying amount of assets sold under agreements to repurchase when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under repurchase agreements exceeds 10 percent of total assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(m)(1)(i)(A)(i)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
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- Definition Mineral properties, net of adjustments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 360 -Section 25 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=96866604&loc=d3e64895-109465 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 + Details
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