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, 2020
USD ($)
Bcfe
well
$ / bbl
$ / MMBTU
Dec. 31, 2019
USD ($)
Bcfe
well
$ / MMBTU
$ / bbl
Dec. 31, 2018
USD ($)
Bcfe
Tcfe
well
$ / bbl
$ / MMBTU
Reserve Quantities [Line Items]      
Interest capitalized | $ $ 907 $ 3,372 $ 4,470
Capitalized general and administrative costs | $ $ 25,000 $ 30,100 $ 37,700
Increase (decrease) in reserve during the period 239.8 1.1 711.2
Decline in performance      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate (1.7) (733.8)  
Lower commodity prices      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate (1,268.4) (296.4)  
Utica Shale      
Reserve Quantities [Line Items]      
Increase (decrease) in reserve during the period 150.6 793.5 556.3
Planned unit development | well 14 72 75
Proved developed and undeveloped reserves, sale of mineral in place     44.9
Utica Shale | Decline in performance      
Reserve Quantities [Line Items]      
Planned unit development | well 48 9  
Proved developed and undeveloped reserve, revision of previous estimate (720.3) (347.2) 8.3
Proved developed, revision of previous estimate 263.8 90.2  
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 | Improved performance      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate     82.4
Utica Shale | Change in ownership interest      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate     67.6
Utica Shale | Increase in pricing      
Reserve Quantities [Line Items]      
Proved developed and undeveloped reserve, revision of previous estimate     27.9
SCOOP Properties      
Reserve Quantities [Line Items]      
Increase (decrease) in reserve during the period 87.8 302.9 90.1
Planned unit development | well 8 37 11
SCOOP Properties | Decline in performance      
Reserve Quantities [Line Items]      
Planned unit development | well 31 22  
SCOOP Properties | Exclusion of PUD locations      
Reserve Quantities [Line Items]      
Planned unit development | well     12
SCOOP Properties | Rescheduled drilling      
Reserve Quantities [Line Items]      
Proved undeveloped reserves, postponement of drilling period     5 years
Louisiana Field      
Reserve Quantities [Line Items]      
Increase (decrease) in reserve during the period     3.0
Planned unit development | well     13
Oil derivatives      
Reserve Quantities [Line Items]      
Price per unit (usd per barrel or MMbtu) | $ / bbl 39.54 55.85 65.56
Natural gas, per MMbtu      
Reserve Quantities [Line Items]      
Price per unit (usd per barrel or MMbtu) | $ / MMBTU 1.99 2.58 3.10
Natural gas liquids      
Reserve Quantities [Line Items]      
Price per unit (usd per barrel or MMbtu) | $ / bbl 15.40 21.25 32.02
Oil and gas properties      
Reserve Quantities [Line Items]      
Interest capitalized | $ $ 900 $ 3,400 $ 4,500
Investment in Grizzly Oil Sands ULC      
Reserve Quantities [Line Items]      
Equity investment, ownership interest 24.50%