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Major Lessee (Details) (USD $) In Thousands, unless otherwise specified | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2011 | Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Major Lessee (Textual) [Abstract] |  |  |  |
Minimum Percentage of revenue derived from major two lessees |  | 46.00% |  |
Total revenue attributable |  | 61.00% |  |
Alpha Natural Resources [Member] |  |  |  |
Revenues from lessees that exceeded ten percent of total revenues |  |  |  |
Revenues |  | $ 107,267 | $ 79,084 | $ 64,626
Percent |  | 28.40% | 26.20% | 25.20%
The Cline Group [Member] |  |  |  |
Revenues from lessees that exceeded ten percent of total revenues |  |  |  |
Revenues |  | $ 64,829 | $ 62,372 | $ 37,369
Percent |  | 17.20% | 20.70% | 14.60%
Percentage of revenue derived from major lessee | 12.00% |  |  |

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- Definition The total amount of revenue recognized for the period from operating leases, including minimum lease revenue, contingent revenue, percentage revenue and sublease revenue. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 13 -Paragraph 19 -Subparagraph b -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6453417&loc=d3e39896-112707 + Details
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