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Summary of Significant Accounting Policies - Results of Operations for Properties (Detail) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Oil And Gas Properties Sold [Abstract]    
Total oil and gas sales $ 13,212 $ 13,535
Total operating expenses [1] (4,391) (14,301)
Operating income (loss) $ 8,821 $ (766)
[1] Includes direct operating expenses, depreciation, depletion and amortization and exploration expense. Excludes interest expense, general and administrative expenses and depreciation, depletion and amortization expense subsequent to the date the assets were designated as held for sale.