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Mineral Rights Schedule of Impairment Expense (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2015 | Sep. 30, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Asset impairment expenses | $ 50,953 | $ 626,838 | $ 3,803 | $ 0 | $ 20,585 | $ 0 | $ 5,624 | $ 0 | $ 681,594 | $ 26,209 | $ 734
Oil And Gas Mineral Rights |  |  |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Asset impairment expenses | 31,900 | 335,700 |  |  |  |  |  |  | 367,576 | 0 | 0
Fair value of impaired assets | 108,000 |  |  |  |  |  |  |  | 108,000 |  |
Coal Mineral Rights |  |  |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Asset impairment expenses | 8,200 | 247,800 | $ 1,500 |  | 16,800 |  |  |  | 257,468 | 16,793 | 734
Fair value of impaired assets | 400 |  |  |  |  |  |  |  | 400 |  |
Hard Mineral Royalty |  |  |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Asset impairment expenses |  | $ 43,400 |  |  |  |  |  |  | 43,402 | 3,013 |
Fair value of impaired assets | $ 0 |  |  |  |  |  |  |  | 0 |  |
Mining Properties and Mineral Rights |  |  |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Asset impairment expenses |  |  |  |  |  |  |  |  | $ 668,446 | $ 19,806 | $ 734
Aggregate Mineral Rights |  |  |  |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Asset impairment expenses |  |  |  |  | $ 3,000 |  |  |  |  |  |

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