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Property and Equipment - Components of Property and Equipment (Detail) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Property, Plant and Equipment [Abstract]    
Proved oil and gas properties, at cost $ 452,400 $ 417,821
Less: Accumulated depletion and depreciation (251,995) (230,331)
Oil and Gas Properties, Net 200,405 187,490
Field and office equipment 26,586 26,902
Less: Accumulated depreciation (19,079) (18,024)
Field and Office Equipment, Net 7,507 8,878
Total Property and Equipment, Net $ 207,912 $ 196,368