Acquisitions and Divestitures - Additional Information (Detail) (USD $)
 12 Months Ended 0 Months Ended 12 Months Ended 0 Months Ended 12 Months Ended
Dec. 31, 2013
Contract
Installment
Dec. 31, 2013
Resolute
Dec. 31, 2013
Nnogc
Jun. 27, 2013
Purchase and sales agreement with Halcon Resources Corporation
Dec. 31, 2013
Aneth Unit
Dec. 31, 2013
Ratherford Unit
Dec. 31, 2013
Aneth and Ratherford Units
Dec. 31, 2013
McElmo Creek Unit
Mar. 22, 2013
New Permian Properties
Dec. 31, 2012
New Permian Properties
Dec. 31, 2012
New Permian Properties
Location 1
Dec. 31, 2012
New Permian Properties
Location 2
Business Acquisition                        
Purchase agreement, purchase price of properties                 $ 258,000,000   $ 117,000,000 $ 133,000,000
Purchase agreement, option fee to buy the balance of the working interest and field and operations                   6,000,000    
Effective date   Jan. 01, 2012                    
Acquired interests   50.00% 50.00%                  
Working interest         13.00% 11.00%            
Cash consideration for acquisitions     100,000,000       75,000,000          
Purchase price allocated to proved oil and gas properties             37,700,000          
Options to purchase     10.00%                  
Purchase and sale agreement relating to the option exercise   5.00%                    
Number of payments of property interest 2                      
Cancellation of purchase     10.00%                  
Option to purchase     10.00%                  
Option exercisable     2017-07                  
Number of purchase option remaining 1                      
Gain or loss recognized 0                      
Working interests         62.00% 59.00%   75.00%        
Reduced working interests               67.50%        
Purchase and sale agreement, effective date       Mar. 01, 2013                
Purchase and sale agreement with Halcón Resources Corporation       $ 70,100,000                
Transaction date       Jul. 15, 2013