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)
12 Months Ended
Dec. 31, 2018
Tcfe
Bcfe
well
$ / bbl
$ / MMBTU
Dec. 31, 2017
Tcfe
Bcfe
well
$ / bbl
$ / MMBTU
Dec. 31, 2016
Tcfe
Bcfe
well
$ / bbl
$ / MMBTU
Reserve Quantities [Line Items]      
Increase (decrease) in reserve during the period | Bcfe 711.2    
Oil derivatives      
Reserve Quantities [Line Items]      
Price per unit (usd per barrel or MMbtu) | $ / bbl 65.56 51.34 42.75
Natural gas, per MMbtu      
Reserve Quantities [Line Items]      
Price per unit (usd per barrel or MMbtu) | $ / MMBTU 3.10 2.98 2.48
Natural gas liquids      
Reserve Quantities [Line Items]      
Price per unit (usd per barrel or MMbtu) | $ / bbl 32.02 18.40 9.91
SCOOP Properties      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, purchase of mineral in place | Tcfe   1.5  
Increase (decrease) in reserve during the period | Bcfe 90.1    
Planned unit development | well 11    
SCOOP Properties | Rescheduled drilling      
Reserve Quantities [Line Items]      
Proved undeveloped reserves, postponement of drilling period   5 years  
SCOOP Properties | Exclusion of PUD locations      
Reserve Quantities [Line Items]      
Planned unit development | well 12    
Utica Shale      
Reserve Quantities [Line Items]      
Increase (decrease) in reserve during the period 556.3 1.6 1.1
Proved developed and undeveloped reserves, sale of mineral in place | Bcfe 44.9    
Planned unit development | well 75 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 | Bcfe (82.4) (201.3) (26.7)
Utica Shale | Higher commodity prices      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate | Bcfe   (214.1)  
Utica Shale | Change in ownership interest      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate | Bcfe (67.6) (95.9)  
Utica Shale | Increase in pricing      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate | Bcfe (27.9)    
Utica Shale | Decline in performance      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate | Bcfe (8.3) (133.0)  
Utica Shale | Rescheduled drilling      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate | Bcfe   (45.7) 17.4
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 (1.0)   227.9
Planned unit development loss | well     35
Development wells drilled | well     67
Utica Shale | Exclusion of PUD locations      
Reserve Quantities [Line Items]      
Planned unit development | well 127    
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      
Reserve Quantities [Line Items]      
Increase (decrease) in reserve during the period | Bcfe 3.0    
Planned unit development | well 13    
Louisiana Field | Rescheduled drilling      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate | Bcfe   (0.6)  
Planned unit development | well   2  
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%