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Income Taxes (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Components of the provision for income taxes |  |  |
Federal | $ 0 | $ 5,698,000 | $ 2,932,000
State | 1,662,000 | 3,398,000 | 1,539,000
Deferred portion of income tax expense (benefit) | 141,708,000 | (192,066,000) | (448,643,000)
Total income tax expense (benefit) | $ 143,370,000 | $ (182,970,000) | $ (444,172,000)
Effective tax rate (as a percent) | 22.00% | 53.20% | 37.00%
Deferred income taxes [Abstract] |  |  |
Deferred tax liabilities, oil and gas properties | $ 218,094,000 | $ 142,467,000 |
Deferred tax liabilities, derivatives assets | 35,247,000 | 0 |
Deferred tax liabilities, other | 4,812,000 | 3,412,000 |
Total deferred tax liabilities | 258,153,000 | 145,879,000 |
Deferred tax assets, derivative liabilities | 0 | 29,463,000 |
Deferred tax assets, credit carryover | 22,554,000 | 22,537,000 |
Deferred tax assets, pension | 6,427,000 | 7,986,000 |
Deferred tax assets, federal and state tax net operating loss carryovers | 4,217,000 | 3,867,000 |
Deferred tax assets, stock compensation | 3,263,000 | 3,545,000 |
Deferred tax assets, other liabilities | 1,497,000 | 1,470,000 |
Total deferred tax assets | 37,958,000 | 68,868,000 |
Deferred tax assets, valuation allowance | (3,083,000) | (2,978,000) |
Net deferred tax assets | 34,875,000 | 65,890,000 |
Total net deferred tax liabilities | 223,278,000 | 79,989,000 |
Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount | 1,000,000 |  |
Proceeds from income tax refunds | 5,900,000 | 5,500,000 |
Reconciliation of unrecognized tax benefits [Roll Forward] |  |  |
Unrecognized tax benefits, Beginning balance | 446,000 | 446,000 | $ 2,782,000
Unrecognized tax benefits, additions for tax positions of prior years | 0 | 0 | 9,000
Unrecognized tax benefits, settlements | 0 | 0 | (2,345,000)
Unrecognized tax benefits, Ending balance | $ 446,000 | 446,000 | $ 446,000
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 | $ 1,331,000 | 3,009,000 |
Net operating loss carryforwards | 79,700,000 |  |
State tax credits [Member] | State and local jurisdiction [Member] |  |  |
Deferred income taxes [Abstract] |  |  |
Tax credit carryforwards | 212,000 |  |
Internal Revenue Service (IRS) [Member] | Domestic tax authority [Member] |  |  |
Deferred income taxes [Abstract] |  |  |
Current federal income tax refundable | 59,000 | $ 37,000 |
Net operating loss carryforwards | 2,300,000 |  |
Internal Revenue Service (IRS) [Member] | R&D tax credit carryforwards [Member] | Domestic tax authority [Member] |  |  |
Deferred income taxes [Abstract] |  |  |
Tax credit carryforwards | 7,400,000 |  |
Internal Revenue Service (IRS) [Member] | Alternative minimum tax credit carryforward [Member] | Domestic tax authority [Member] |  |  |
Deferred income taxes [Abstract] |  |  |
Tax credit carryforwards | $ 15,600,000 |  |

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