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Long-Term Debt - Additional Information (Detail) (USD $)
 3 Months Ended 6 Months Ended 24 Months Ended 6 Months Ended 6 Months Ended 0 Months Ended 24 Months Ended
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Senior Unsecured Debt [Member]
Dec. 31, 2012
Senior Unsecured Debt [Member]
Jun. 30, 2014
Second Amended Credit Facility [Member]
Mar. 27, 2014
Second Amended Credit Facility [Member]
Apr. 05, 2013
Second Amended Credit Facility [Member]
Jun. 30, 2014
Current Ratio [Member]
Second Amended Credit Facility [Member]
Jun. 30, 2014
Minimum [Member]
Second Amended Credit Facility [Member]
Sep. 24, 2013
2022 Notes [Member]
Senior Unsecured Debt [Member]
Dec. 31, 2012
2019 Notes [Member]
Senior Unsecured Debt [Member]
Dec. 31, 2012
2021 Notes [Member]
Senior Unsecured Debt [Member]
Dec. 31, 2012
2023 Notes [Member]
Senior Unsecured Debt [Member]
Dec. 31, 2013
2023 Notes [Member]
Senior Unsecured Debt [Member]
Debt Disclosure [Line Items]                                
Principal debt amount                       $ 1,000,000,000.0 $ 400,000,000.0 $ 400,000,000.0   $ 400,000,000.0
Stated interest rate                       6.875% 7.25% 6.50%   6.875%
Debt instrument, maturity date             Apr. 05, 2018         Mar. 15, 2022 Feb. 01, 2019 Nov. 01, 2021 Jan. 15, 2023  
Net proceeds from issuance of notes           1,175,800,000           983,600,000        
Exchange term                       360 days        
Exchange increase in interest rate                       1.00%        
Line of credit facility maximum increase to aggregate commitments               1,750,000,000 1,500,000,000              
Senior unsecured notes payment frequency         semi-annually                      
Redemption percentage, maximum         35.00%                      
Redemption term         180 days                      
Percentage of minimum outstanding principal amount         65.00%                      
Event of default by payment default ($10.0 million or more)         10,000,000.0                      
Event of default by final judgments (in excess of $10.0 million)         10,000,000.0                      
Line of credit facility, maximum borrowing capacity               1,500,000,000.0                
Line of credit facility, capacity available for specific purpose other than for trade purchases             2,500,000,000                  
Percentage of the reserve value of assets as determined by reserve reports (at least 80%)                     80.00%          
Commitment fee of borrowing base capacity not utilized             0.375%                  
Ratio of EBITDAX to interest expense necessary to maintain covenants                     2.5          
Minimum current ratio                   1.0            
Line of credit facility, amount outstanding             100,000,000                  
Outstanding letters of credit             5,200,000                  
Line of credit facility, remaining borrowing capacity             1,394,800,000                  
Weighted average interest rate             1.70%                  
Deferred financing costs 38,700,000   38,700,000                          
Amortization of deferred financing costs $ 1,600,000 $ 1,000,000 $ 3,200,000 $ 1,900,000