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Income Taxes (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Components of the provision for income taxes |  |  |
Federal | $ 5,698,000 | $ 2,932,000 | $ 0
State | 3,398,000 | 1,539,000 | 1,571,000
Deferred portion of income tax benefit | (192,066,000) | (448,643,000) | (276,722,000)
Total income tax benefit | $ (182,970,000) | $ (444,172,000) | $ (275,151,000)
Effective tax rate (as a percent) | 53.20% | 37.00% | 38.10%
Deferred income taxes [Abstract] |  |  |
Deferred tax liabilities, oil and gas properties | $ 142,467,000 | $ 518,394,000 |
Deferred tax liabilities, other | 3,412,000 | 7,733,000 |
Total deferred tax liabilities | 145,879,000 | 526,127,000 |
Deferred tax assets, derivative liabilities | 29,463,000 | 31,349,000 |
Deferred tax assets, credit carryover | 22,537,000 | 12,448,000 |
Deferred tax assets, pension | 7,986,000 | 10,366,000 |
Deferred tax assets, federal and state tax net operating loss carryovers | 3,867,000 | 151,343,000 |
Deferred tax assets, stock-compensation | 3,545,000 | 10,083,000 |
Deferred tax assets, other liabilities | 1,470,000 | 201,000 |
Total deferred tax assets | 68,868,000 | 215,790,000 |
Deferred tax assets, valuation allowance | (2,978,000) | (5,335,000) |
Net deferred tax assets | 65,890,000 | 210,455,000 |
Total net deferred tax liabilities | 79,989,000 | 315,672,000 |
Proceeds from income tax refunds | 5,500,000 |  |
Net R&D tax credit recorded for IRS settlement |  | 2,000,000 |
Reconciliation of unrecognized tax benefits [Roll Forward] |  |  |
Unrecognized tax benefits, Beginning balance | 446,000 | 2,782,000 | $ 1,582,000
Unrecognized tax benefits, additions for tax positions of prior years | 0 | 9,000 | 1,200,000
Unrecognized tax benefits, settlements | 0 | (2,345,000) | 0
Unrecognized tax benefits, Ending balance | $ 446,000 | 446,000 | $ 2,782,000
Tax year 2017 [Member] |  |  |
Deferred income taxes [Abstract] |  |  |
Federal enacted statutory income tax rate, percent | 35.00% |  |
Future tax years [Member] |  |  |
Deferred income taxes [Abstract] |  |  |
Federal enacted statutory income tax rate, percent | 21.00% |  |
State and local jurisdiction [Member] |  |  |
Deferred income taxes [Abstract] |  |  |
Current state income tax payable | $ 3,009,000 | 1,181,000 |
Net operating loss carryforwards | 71,800,000 |  |
State tax credits [Member] | State and local jurisdiction [Member] |  |  |
Deferred income taxes [Abstract] |  |  |
Tax credit carryforwards | 283,000 |  |
Internal Revenue Service (IRS) [Member] | Domestic tax authority [Member] |  |  |
Deferred income taxes [Abstract] |  |  |
Current federal income tax refundable | 37,000 | $ 644,000 |
Net operating loss carryforwards | 1,300,000 |  |
Internal Revenue Service (IRS) [Member] | R&D tax credit carryforwards [Member] | Domestic tax authority [Member] |  |  |
Deferred income taxes [Abstract] |  |  |
Tax credit carryforwards | 7,200,000 |  |
Internal Revenue Service (IRS) [Member] | Alternative minimum tax credit carryforward [Member] | Domestic tax authority [Member] |  |  |
Deferred income taxes [Abstract] |  |  |
Tax credit carryforwards | $ 15,700,000 |  |

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