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Asset Retirement Obligations (ARO Activity) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Carrying amount of the asset retirement obligations, balance at beginning of period $ 43,951 $ 41,732
Liabilities settled during the period (1,179) (1,053)
Accretion expense 3,522 3,300
Revision of estimated cash flows (292) (28)
Carrying amount of the asset retirement obligations, balance at end of period 46,002 43,951
Operating Segments | Coal Mining customer    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Carrying amount of the asset retirement obligations, balance at beginning of period 26,898 25,040
Liabilities settled during the period (223) (184)
Accretion expense 2,190 1,996
Revision of estimated cash flows (405) 46
Carrying amount of the asset retirement obligations, balance at end of period 28,460 26,898
Unallocated Items    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Carrying amount of the asset retirement obligations, balance at beginning of period 17,053 16,692
Liabilities settled during the period (956) (869)
Accretion expense 1,332 1,304
Revision of estimated cash flows 113 (74)
Carrying amount of the asset retirement obligations, balance at end of period $ 17,542 $ 17,053