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Asset Retirement Obligation - Information Related to Asset Retirement Obligations (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Asset Retirement Obligation Disclosure [Abstract]    
Beginning Balance $ 226,137 $ 222,989
Additions to asset retirement obligations 658 2,529
Accretion expense 4,135 4,260
Liabilities settled (8,054) (3,641)
Ending Balance $ 222,876 $ 226,137