Annual report pursuant to Section 13 and 15(d)

Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) - Narrative (Details)

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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
Dec. 31, 2016
USD ($)
MMcfe
well
$ / MMBTU
$ / bbl
Dec. 31, 2015
MMcfe
$ / MMBTU
$ / bbl
Dec. 31, 2014
MMcfe
$ / MMBTU
$ / bbl
Reserve Quantities [Line Items]      
Future development costs estimated to be spent year one | $ $ 401.5    
Future development costs estimated to be spent year two | $ 331.4    
Future development costs estimated to be spent year three | $ $ 192.7    
Paloma and AEU      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, purchase of mineral in place 371,663    
Rhino Exploration, LLC, Utica Shale Properties      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, purchase of mineral in place     12,019
Oil derivatives      
Reserve Quantities [Line Items]      
Price per unit (usd per barrel or MMbtu) | $ / bbl 42.75 50.28 94.99
Natural gas, per MMbtu      
Reserve Quantities [Line Items]      
Price per unit (usd per barrel or MMbtu) | $ / MMBTU 2.48 2.59 4.35
Natural gas liquids      
Reserve Quantities [Line Items]      
Price per unit (usd per barrel or MMbtu) | $ / bbl 9.91 13.21 44.84
Utica Shale      
Reserve Quantities [Line Items]      
Increase (decrease) in reserve during the period 1,100,000 1,044,500 786,347
Planned unit development | well 34    
Proved developed and undeveloped reserve, production increase, percentage (Energy) 14.50%    
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, Productive and Non-Productive | well 67    
Utica Shale | Rescheduled drilling      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate 17,400    
Planned unit development | well 4    
Proved undeveloped reserves, postponement of drilling period 5 years    
Utica Shale | Improved performance      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate 26,700    
Southern Louisiana and Utica Fields      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate (444,314)   (15,837)
Proved undeveloped reserves, postponement of drilling period     5 years
Investment in Grizzly Oil Sands ULC      
Reserve Quantities [Line Items]      
Equity investment ownership interest 24.9999%