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Note 4 - Other Long-term Assets - Other Long-term Assets (Details) - USD ($) $ in Thousands | Mar. 31, 2022 | Dec. 31, 2021
--- | --- | ---
Advanced coal royalties | $ 6,668 | $ 6,678
Other | 1,665 | 1,694
Total other assets | $ 8,333 | $ 8,372

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- Definition Amount of other miscellaneous assets expected to be realized or consumed after one year or normal operating cycle, if longer. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | debit
Period Type: | instant

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- Definition Amount of noncurrent assets classified as other. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(17)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition Carrying amount as of the balance sheet date of capitalized amounts paid for mineral royalties which will be charged against earnings after one year or beyond the normal operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(17)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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