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Commitments - Reconciliation of Liability for Plugging and Abandonment Costs (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]    
Asset retirement obligation $ 21,118 $ 21,334
Liabilities incurred 4 4
Liabilities settled (1,286) (1,442)
Liabilities divested (5,731)  
Accretion expense 856 1,120
Revisions in estimated liabilities (1,301) 102
Asset retirement obligation $ 13,660 $ 21,118