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Asset Retirement Obligations (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Balance, Beginning of Year $ 68,454 $ 38,554
Obligations Divested 703 0
Accretion Expense 11,067 9,458
Obligations Incurred 2,806 2,933
Obligations Settled (7,905) (4,231)
Revisions in Estimated Cash Flows 19,449 21,740
Balance, End of Year $ 93,168 $ 68,454