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Note 2 - Long-lived Asset Impairments (Details Textual) - USD ($) $ in Thousands | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Aug. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2019
Asset Impairment Charges, Total |  |  | $ 0 | $ 1,799 | $ 0 | $ 1,799 |
Hourglass Sands [Member] |  |  |  |  |  |  |
Asset Impairment Charges, Total | $ 1,800 | $ 2,900 |  | $ 1,800 |  |  | $ 2,900
Mineral Properties, Net, Total |  | $ 1,900 |  |  |  |  | $ 1,900

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- Definition Mineral properties, net of adjustments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -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://fasb.org/us-gaap/role/ref/legacyRef -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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