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Other Long-Term Obligations and Commitments - Reconciliation of Liability for Plugging and Abandonment Costs (Detail)
$ in Thousands
9 Months Ended
Sep. 30, 2018
USD ($)
Commitments and Contingencies Disclosure [Abstract]  
Asset retirement obligation at beginning of period $ 23,578
Liabilities incurred 42
Liabilities settled (1,967)
Accretion expense 840
Asset retirement obligation at end of period $ 22,493