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Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) - Narrative (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2017 USD ($) MMcfe well $ / bbl $ / MMBTU | Dec. 31, 2016 MMcfe well $ / bbl $ / MMBTU | Dec. 31, 2015 MMcfe $ / bbl $ / MMBTU
Reserve Quantities [Line Items] |  |  |
Future development costs estimated to be spent during 2018 | $ | $ 551.0 |  |
Future development costs estimated to be spent during 2019 | $ | 458.8 |  |
Future development costs estimated to be spent during 2020 | $ | $ 514.5 |  |
Oil derivatives |  |  |
Reserve Quantities [Line Items] |  |  |
Price per unit (usd per barrel or MMbtu) | $ / bbl | 51.34 | 42.75 | 50.28
Natural gas, per MMbtu |  |  |
Reserve Quantities [Line Items] |  |  |
Price per unit (usd per barrel or MMbtu) | $ / MMBTU | 2.98 | 2.48 | 2.59
Natural gas liquids |  |  |
Reserve Quantities [Line Items] |  |  |
Price per unit (usd per barrel or MMbtu) | $ / bbl | 18.40 | 9.91 | 13.21
SCOOP Properties |  |  |
Reserve Quantities [Line Items] |  |  |
Proved developed and undeveloped reserve, purchase of mineral in place | 1,500,000 |  |
Utica Shale |  |  |
Reserve Quantities [Line Items] |  |  |
Increase (decrease) in reserve during the period | 1,600,000 | 1,100,000 | 1,044,500
Planned unit development | well | 10 | 34 |
Proved developed and undeveloped reserve, production increase, percentage |  | 14.50% |
Utica Shale | Improved performance |  |  |
Reserve Quantities [Line Items] |  |  |
Proved developed and undeveloped reserve, revision of previous estimate | (201,300) | (26,700) |
Utica Shale | Higher commodity prices |  |  |
Reserve Quantities [Line Items] |  |  |
Proved developed and undeveloped reserve, revision of previous estimate | (214,100) |  |
Utica Shale | Change in ownership interest |  |  |
Reserve Quantities [Line Items] |  |  |
Proved developed and undeveloped reserve, revision of previous estimate | (95,900) |  |
Utica Shale | Decline in performance |  |  |
Reserve Quantities [Line Items] |  |  |
Proved developed and undeveloped reserve, revision of previous estimate | (133,000) |  |
Utica Shale | Rescheduled drilling |  |  |
Reserve Quantities [Line Items] |  |  |
Proved developed and undeveloped reserve, revision of previous estimate | (45,700) | 17,400 |
Planned unit development | well |  | 4 |
Proved undeveloped reserves, postponement of drilling period |  | 5 years |
Utica Shale | Lower commodity prices |  |  |
Reserve Quantities [Line Items] |  |  |
Proved developed and undeveloped reserve, revision of previous estimate |  | 227,900 |
Planned unit development loss | well |  | 35 |
Development wells drilled | well |  | 67 |
Utica Shale | Exclusion of PUD locations |  |  |
Reserve Quantities [Line Items] |  |  |
Proved developed and undeveloped reserve, revision of previous estimate |  |  | 444,314
Utica Shale | Gulfport | Rescheduled drilling |  |  |
Reserve Quantities [Line Items] |  |  |
Planned unit development | well | 5 |  |
Utica Shale | Third Party | Rescheduled drilling |  |  |
Reserve Quantities [Line Items] |  |  |
Planned unit development | well | 5 |  |
Louisiana Field | Rescheduled drilling |  |  |
Reserve Quantities [Line Items] |  |  |
Proved developed and undeveloped reserve, revision of previous estimate | (600) |  |
Planned unit development | well |  | 2 |
Proved undeveloped reserves, postponement of drilling period |  | 5 years |
Paloma and AEU |  |  |
Reserve Quantities [Line Items] |  |  |
Proved developed and undeveloped reserve, purchase of mineral in place |  |  | 371,663
Investment in Grizzly Oil Sands ULC |  |  |
Reserve Quantities [Line Items] |  |  |
Equity investment ownership interest | 24.9999% |  |

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