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Summary of Significant Accounting Policies - Summary of Changes in Reserve for Future Abandonment Costs (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Asset Retirement Obligations Noncurrent [Abstract]    
Future abandonment costs — beginning of period $ 10,407 $ 15,804
Accretion expense 140 220
New wells placed on production 2 1
Liabilities settled and assets disposed of (60) (12)
Future abandonment costs — end of period $ 10,489 $ 16,013