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SEGMENT INFORMATION - General Information (Details) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2020 segment | Feb. 08, 2019 USD ($) | Jul. 19, 2017 USD ($)
Reportable segment results |  |  |
Number of reportable segments | 3 |  |
Number of coal reportable segments | 2 |  |
Number of mining complex | 7 |  |
Kodiak |  |  |
Reportable segment results |  |  |
Equity securities | $ |  | $ 0.0 | $ 100.0

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- Definition Amount of investment in equity security without readily determinable fair value. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=120269885&loc=SL75117539-209714 + Details
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- Definition Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8672-108599 + Details
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- Details
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