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Asset Impairments (Details) (USD $) | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Dec. 31, 2011 | Sep. 30, 2011 | Dec. 31, 2011 | Dec. 31, 2010
Net book value and fair values of the assets |  |  |  |
Coal and other mineral rights, net book value | $ 1,257,501,000 |  | $ 1,257,501,000 | $ 1,281,636,000
Intangible assets, net book value | 75,164,000 |  | 75,164,000 | 161,931,000
Plant and equipment, net book value | 46,185,000 |  | 46,185,000 | 62,348,000
Asset Impairment (Textual) [Abstract] |  |  |  |
Non-recoupable minimum royalty balance |  |  | 24,100,000 |
Asset impairment charges | 70,400,000 | 90,900,000 | 161,336,000 |
Gatling LLC West Verginia [Member] |  |  |  |
Net book value and fair values of the assets |  |  |  |
Coal and other mineral rights, net fair value | 6,618,000 |  | 6,618,000 |
Intangible assets, net fair value | 0 |  | 0 |
Plant and equipment, net fair value | 2,600,000 |  | 2,600,000 |
Total, net fair value | 9,218,000 |  | 9,218,000 |
Coal and other mineral rights, net book value | 76,003,000 |  | 76,003,000 |
Intangible assets, net book value | 43,855,000 |  | 43,855,000 |
Plant and equipment, net book value | 7,775,000 |  | 7,775,000 |
Total, net book value | 127,633,000 |  | 127,633,000 |
Asset Impairment (Textual) [Abstract] |  |  |  |
Non-recoupable minimum royalty balance |  |  | 24,100,000 |
Non-recoupable minimum royalty payments |  |  | 3,400,000 |
Net impairment |  |  | 90,900,000 |
Asset impairment charges |  |  | 118,400,000 |
Gatling LLC Ohio [Member] |  |  |  |
Net book value and fair values of the assets |  |  |  |
Coal and other mineral rights, net fair value | 20,035,000 |  | 20,035,000 |
Intangible assets, net fair value | 0 |  | 0 |
Plant and equipment, net fair value | 2,947,000 |  | 2,947,000 |
Total, net fair value | 22,982,000 |  | 22,982,000 |
Coal and other mineral rights, net book value | 56,769,000 |  | 56,769,000 |
Intangible assets, net book value | 33,670,000 |  | 33,670,000 |
Plant and equipment, net book value | 2,947,000 |  | 2,947,000 |
Total, net book value | 93,386,000 |  | 93,386,000 |
Asset Impairment (Textual) [Abstract] |  |  |  |
Recoupable minimum royalty balance |  |  | 9,600,000 |
Asset impairment charges |  |  | $ 70,400,000 |

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