Quarterly report pursuant to Section 13 or 15(d)

Accounting Policies (Narrative II) (Detail)

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Accounting Policies (Narrative II) (Detail) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Sep. 30, 2014
Jun. 30, 2015
Sep. 30, 2015
Sep. 30, 2014
Dec. 31, 2014
Quantifying Misstatement in Current Year Financial Statements [Line Items]                
Impairment Of Oil And Gas Properties $ 18,000 $ 500   $ 0   $ 29,200 $ 0  
Asset Impairment Charge Percent   9.00%           7.00%
Net Income Loss (33,668)     3,109   $ (77,877) 20,788  
Net Income Loss, percent           9.00%    
Depreciation Depletion And Amortization 8,259     $ 4,289   $ 23,493 $ 15,444  
Immaterial Understatement [Member]                
Quantifying Misstatement in Current Year Financial Statements [Line Items]                
Impairment Of Oil And Gas Properties               $ 7,000
Net Income Loss $ 100              
Net Income Loss, percent 1.00%             9.00%
Immaterial Overstatement [Member]                
Quantifying Misstatement in Current Year Financial Statements [Line Items]                
Impairment Of Oil And Gas Properties     $ 3,100   $ 2,600      
Asset Impairment Charge Percent     57.00%   23.00%      
Net Income Loss     $ 3,500   $ 3,500      
Net Income Loss, percent     9.00%   8.00%