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Divestitures (Narrative) (Details) - Oil and Natural Gas [Member] - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Segment Reporting Information [Line Items]    
Proceeds from Sale of Other Assets $ 7,100  
Proceeds from non-core oil and natural gas asset sales, net of related expenses $ 1,700 $ 600