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Note 2 - Long-lived Asset Impairments (Details Textual) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2019
Asset Impairment Charges, Total | $ 1,799 |  |  |  | $ 0 | $ 1,799 | $ 0 |
Carlisle Mine [Member] |  |  |  |  |  |  |  |
Asset Impairment Charges, Total |  |  | $ 0 | $ 65,700 |  |  |  |
Mineral Properties, Net, Total | 1,800 |  |  | 1,800 |  | 1,800 |  | $ 1,800
Equipment, Redeployed |  |  | 23,000 |  |  |  |  |
Carlisle Mine [Member] | Closing of Mine [Member] |  |  |  |  |  |  |  |
Restructuring and Related Costs, Incurred Cost, Total |  | $ 1,100 | $ 1,100 |  |  |  |  |
Bulldog Reserves [Member] |  |  |  |  |  |  |  |
Asset Impairment Charges, Total |  |  |  | $ 9,200 |  |  |  |
Hourglass Sands [Member] |  |  |  |  |  |  |  |
Asset Impairment Charges, Total | 1,800 |  |  |  |  |  |  | $ 2,900
Mineral Properties, Net, Total | $ 1,900 |  |  |  |  | $ 1,900 |  |

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- Definition Discloses the amount charged against the accrued restructuring reserves, or earnings if not previously accrued, during the period for the specified type of restructuring cost. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 5.P.4(b)(1)) -URI http://asc.fasb.org/extlink&oid=115931487&loc=d3e140904-122747 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 5.P.4(d)) -URI http://asc.fasb.org/extlink&oid=115931487&loc=d3e140904-122747 + Details
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