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 Thousands
12 Months Ended
Dec. 31, 2019
USD ($)
Bcfe
well
$ / bbl
$ / MMBTU
Dec. 31, 2018
USD ($)
Tcfe
Bcfe
well
$ / bbl
$ / MMBTU
Dec. 31, 2017
USD ($)
Tcfe
Bcfe
well
$ / bbl
$ / MMBTU
Reserve Quantities [Line Items]      
Interest capitalized | $ $ 3,372 $ 4,470 $ 9,470
Interest cost capitalized, acquisition and development activities | $ $ 30,100 $ 37,700 $ 35,700
Increase (decrease) in reserve during the period 1,100 711.2  
Proved developed and undeveloped reserve, decrease, percentage 0.50%    
Decline in performance      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate 733.8    
Lower commodity prices      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate 296.4    
Oil derivatives      
Reserve Quantities [Line Items]      
Price per unit (usd per barrel or MMbtu) | $ / bbl 55.85 65.56 51.34
Natural gas, per MMbtu      
Reserve Quantities [Line Items]      
Price per unit (usd per barrel or MMbtu) | $ / MMBTU 2.58 3.10 2.98
Natural gas liquids      
Reserve Quantities [Line Items]      
Price per unit (usd per barrel or MMbtu) | $ / bbl 21.25 32.02 18.40
SCOOP Properties      
Reserve Quantities [Line Items]      
Increase (decrease) in reserve during the period 302.9 90.1  
Planned unit development | well 37 11  
Proved developed and undeveloped reserve, purchase of mineral in place | Tcfe     1.5
SCOOP Properties | Decline in performance      
Reserve Quantities [Line Items]      
Planned unit development | well 22    
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 793.5 556.3 1.6
Planned unit development | well 72 75 10
Proved developed and undeveloped reserves, sale of mineral in place   44.9  
Utica Shale | Improved performance      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate   (82.4) (201.3)
Utica Shale | Higher commodity prices      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate     (214.1)
Utica Shale | Change in ownership interest      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate   (67.6) (95.9)
Utica Shale | Increase in pricing      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate   (27.9)  
Utica Shale | Decline in performance      
Reserve Quantities [Line Items]      
Proved developed, revision of previous estimate 90.2    
Planned unit development | well 9    
Proved developed and undeveloped reserve, revision of previous estimate 347.2 (8.3) (133.0)
Utica Shale | Rescheduled drilling      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate     (45.7)
Utica Shale | Lower commodity prices      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate | Tcfe   (1.0)  
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   3.0  
Planned unit development | well   13  
Louisiana Field | Rescheduled drilling      
Reserve Quantities [Line Items]      
Planned unit development | well     2
Proved developed and undeveloped reserve, revision of previous estimate     (0.6)
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%    
Oil and gas properties      
Reserve Quantities [Line Items]      
Interest capitalized | $ $ 3,400 $ 4,500 $ 9,500