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Property, Plant and Equipment - Assets Amortized by Units of Production (Details) - USD ($)
$ in Thousands
Dec. 31, 2021
Dec. 31, 2020
Property, Plant and Equipment [Line Items]    
Unproved Gas Properties $ 730,400 $ 725,705
Total 11,362,102 10,963,996
Assets amortized by units of production    
Property, Plant and Equipment [Line Items]    
Unproved Gas Properties 730,400 725,705
Advance Royalties 6,885 9,676
Total $ 737,285 $ 735,381