Organization and Business (Details) - Item	3 Months Ended
Sep. 30, 2015	Dec. 31, 2014
Schedule of Capitalization, Equity [Line Items]
Number of surface coal mines operated by entity	3
Number of major development projects	2
Percentage of electricity generated in the U.S. from the coal produced		4.00%

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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