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Asset Retirement Obligations (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018
Segment Reporting Information [Line Items] |  |
Increase (decrease) in asset retirement obligation | $ (5,400) |
Company transferred | 3,400 |
Escrow account | 2,400 |
Net loss on the transactions | 400 |
Revision of estimated cash flows | 3,145 | $ (3,495)
Bellaire |  |
Segment Reporting Information [Line Items] |  |
Fair value of trust assets | 10,100 | 5,000
Operating Segments | Coal Mining |  |
Segment Reporting Information [Line Items] |  |
Revision of estimated cash flows | 3,145 | $ (2,777)
Centennial |  |
Segment Reporting Information [Line Items] |  |
Increase (decrease) in asset retirement obligation | 2,000 |
Revision of estimated cash flows | 2,326 |
Centennial | Operating Segments | Coal Mining |  |
Segment Reporting Information [Line Items] |  |
Revision of estimated cash flows | $ 2,479 |

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- Definition Asset Retirement Obligation, Amount Transferred To Escrow + References No definition available. + Details
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- Definition Asset Retirement Obligation, Gain (Loss) Recognized On Transaction + References No definition available. + Details
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- Definition Amount of cash paid during the period to settle an asset retirement obligation. Amounts paid to settle an asset retirement obligation are generally included in the operating section of the Statement of Cash Flows. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 17 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3367-108585 + Details
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- Definition Carrying amount of an asset that is legally restricted for purposes of settling an asset retirement obligation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Amount of increase (decrease) in asset retirement obligations. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 35 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6392603&loc=d3e7123-110846 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(4) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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