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Significant Acquisitions (Details Textuals) (USD $) | 3 Months Ended | 12 Months Ended |  | 12 Months Ended |  | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | --- | ---
Dec. 31, 2011 | Sep. 30, 2011 | Jun. 30, 2011 | Mar. 31, 2011 | Dec. 31, 2010 | Sep. 30, 2010 | Jun. 30, 2010 | Mar. 31, 2010 | Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009 | Feb. 19, 2012 | Dec. 31, 2011 BRP LLC [Member] | Dec. 31, 2010 BRP LLC [Member] | Jun. 30, 2010 BRP LLC [Member] | Sep. 30, 2009 Colt [Member] T | Dec. 31, 2011 Colt [Member] T
Acquisitions (Textual) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Purchase price |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 42,500,000 | $ 255,000,000 |
Amount paid at closing |  |  |  |  |  |  |  |  |  |  |  | 70,000,000 |  |  |  |  | 175,000,000
Percentage of income interest as a result of acquisition |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 51.00% |  |
Percentage of minority voting interest of IPC |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 49.00% |  |
Assets fair value using a cash flows approach |  |  |  |  |  |  |  |  |  |  |  |  | 38,300,000 |  |  |  |
Total asset fair value |  |  |  |  |  |  |  |  |  |  |  |  | 47,200,000 |  |  |  |
Non-controlling interests, Estimated fair value |  |  |  |  |  |  |  |  |  |  |  |  | 4,700,000 |  |  |  |
Net income | (19,357,000) | (30,559,000) | 56,206,000 | 45,282,000 | 42,506,000 | 40,153,000 | 41,611,000 | 30,191,000 | 54,026,000 | 154,461,000 | 114,080,000 |  | 5,200,000 | 2,300,000 |  |  |
Transaction expenses related to acquisition |  |  |  |  |  |  |  |  |  |  |  |  | $ 600,000 | $ 2,500,000 |  |  |
Coal reserve agreed to acquire under partnership agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 200,000,000 | 92,100,000

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