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Subsequent Events - Additional Information (Detail) (USD $)
 9 Months Ended 1 Months Ended 1 Months Ended 0 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Drilling contracts [Member]
Sep. 30, 2013
Second Amended Credit Facility [Member]
Apr. 05, 2013
Second Amended Credit Facility [Member]
Mar. 31, 2013
Second Amended Credit Facility [Member]
Sep. 30, 2013
West Williston Acquisition [Member]
Oct. 10, 2013
Subsequent Event [Member]
Oct. 31, 2013
Subsequent Event [Member]
Drilling contracts [Member]
Oct. 02, 2013
Subsequent Event [Member]
Second Amended Credit Facility [Member]
Oct. 02, 2013
Subsequent Event [Member]
West Williston Acquisition [Member]
acre
Subsequent Event [Line Items]                      
Acres acquired                     136,000
Acquisition, consideration transferred                     $ 1,478,600,000
Acquisition, consideration transferred, deposit             72,500,000        
Proceeds from credit facility 160,000,000 0               440,000,000  
Line of credit facility, amount outstanding       160,000,000           605,200,000  
Line of credit facility, remaining borrowing capacity       1,334,800,000           894,800,000  
Line of credit facility, maximum borrowing capacity         1,250,000,000 750,000,000       1,500,000,000  
Payments upon early contract termination     24,900,000           9,700,000    
Purchase Commitment, Remaining Minimum Amount Committed               $ 3,600,000