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Income Taxes (Narrative) (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Operating Loss Carryforwards [Line Items] |  |  |
Alternative minimum tax credits | $ 23,629,000 | $ 24,053,000 | $ 7,968,000
Foreign tax credit carryforwards | 2,074,000 | 2,074,000 | 2,074,000
Valuation allowance of deferred tax assets | 281,782,000 | 3,145,000 | 4,743,000
Change in deferred tax asset valuation | 278,637,000 | 0 | 0
Impairment of oil and gas properties | 1,440,418,000 | 0 | 0
Federal and state income taxes payable | 0 | 17,700,000 |
Diamondback |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Taxable gain on contribution |  | 203,300,000 |
Deferred tax expense |  |  | 35,700,000
Gain from sale of equity investment |  |  | 120,000,000
Current tax expense |  |  | $ 13,200,000
Change in deferred tax asset valuation |  | 79,400,000 |
Investment in Blackhawk Midstream LLC |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Gain from sale of equity investment |  | 83,700,000 |
Change in deferred tax asset valuation |  | $ 32,300,000 |
Federal |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Net operating loss carryforward | 132,000,000 |  |
Louisiana |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Net operating loss carryforward | $ 88,600,000 |  |

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