Quarterly report pursuant to Section 13 or 15(d)

Asset Retirement Obligations (Details)

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Asset Retirement Obligations (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Asset Retirement Obligations    
Asset retirement obligations - beginning of period $ 54,452  
Obligations incurred 70  
Accretion expense 788 $ 1,104
Asset retirement obligations - end of period $ 55,310