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Concentrations of Credit Risk (Details) (Customer Concentration Risk [Member]) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Sales Revenue, Goods, Net [Member] | XCoal Energy and Resources [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Concentration Risk, Customer | 344617 | 495242 | 382843
Sales Revenue, Goods, Net [Member] | Duke Energy [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Concentration Risk, Customer | 394849 | 346424 |
Accounts Receivable [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Concentration Risk, Customer | 259817 | 332574 |
Accounts Receivable [Member] | Gas Customers [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Concentration Risk, Customer | 117985 | 71441 |
Accounts Receivable [Member] | All Other [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Concentration Risk, Customer | 4279 | 43199 |
Accounts Receivable [Member] | Coal Brokers and Distributors [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Concentration Risk, Customer | 41983 | 52233 |
Accounts Receivable [Member] | Steel and Coke Producers [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Concentration Risk, Customer | 10043 | 10963 |
Accounts Receivable [Member] | Steam Coal Utilities [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Concentration Risk, Customer | 85527 | 154738 |

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- Definition Description of risks that arise due to the volume of business transacted with a particular customer. At a minimum, the description informs financial statement users of the general nature of the risk, but excludes "Information about Major Customers" that may be disclosed elsewhere (for instance, segment disclosures). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 16 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6327-108592 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 18 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592 + Details
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