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Asset Retirement Obligations - Roll-Forward (Details)
$ in Thousands
9 Months Ended
Sep. 30, 2023
USD ($)
Change in asset retirement obligations  
Asset retirement obligations at the beginning of year $ 797,762
Changes attributable to:  
Accretion expense 32,763
Settlements (5,750)
Estimated cash flow revisions 70,405
Asset retirement obligations at the end of year $ 895,180