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Asset Retirement Obligations (AROs) - Change in Asset Retirement Obligation (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Beginning Balance $ 12,656 $ 9,117
New Obligations Recognized 8,062 0
Adjustments Due to Revisions in Cash Flow Estimates 3,110 3,099
Accrued Accretion 570 440
Settlements (577) 0
Ending Balance $ 23,821 $ 12,656