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Property, Plant, and Equipment - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Property, Plant and Equipment [Line Items]        
Impairment of Exploration and Production Properties $ 0 $ 0 $ 0 $ 61,849
Southwest Pennsylvania CBM Asset Group [Member]        
Property, Plant and Equipment [Line Items]        
Impairment of Exploration and Production Properties       $ 61,849