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Coal and Other Mineral Rights (Tables) | 12 Months Ended
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Dec. 31, 2011
Coal and Other Mineral Rights [Abstract] |
Coal and other mineral rights |
|  | December 31, 2011 |  |  | December 31, 2010 |
|  | (In thousands) |
Coal and other mineral rights |  | $ | 1,645,451 |  |  | $ | 1,629,286 |
Less accumulated depletion and amortization |  |  | (387,950 | ) |  |  | (347,650 | )
Net book value |  | $ | 1,257,501 |  |  | $ | 1,281,636 |
|  | For the years ended December 31, |
|  | 2011 |  |  | 2010 |  |  | 2009 |
|  | (In thousands) |
Total depletion and amortization expense on coal and other mineral interests |  | $ | 47,230 |  |  | $ | 38,501 |  |  | $ | 48,591 |

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