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Commitments and Contingencies - Additional Information (Detail) (USD $)
 12 Months Ended
Dec. 31, 2013
Y
Contract
Dec. 31, 2012
Dec. 31, 2011
Commitments And Contingencies Disclosure [Line Items]      
Rent expense under operating leases $ 13,100,000 $ 13,800,000 $ 18,600,000
Number of drilling rigs used under drilling contracts 3    
Maximum period of drilling contracts in years 2    
Maximum penalties on early termination of drilling contracts 10,900,000    
Minimum remaining terms of leases on undeveloped acreage, in years 3 years    
Maximum remaining terms of leases on undeveloped acreage, in years 5 years    
Legal Settlement for Drummond Lawsuit 87,500,000    
2015 | Appalachia
      
Commitments And Contingencies Disclosure [Line Items]      
Transporation commitments contingent upon pipeline construction or modification in bbl 10,000    
2016 | Appalachia
      
Commitments And Contingencies Disclosure [Line Items]      
Transporation commitments contingent upon pipeline construction or modification in bbl 20,000    
Drilling
      
Commitments And Contingencies Disclosure [Line Items]      
Contractual Obligation, Due in Next Twelve Months 9,000,000    
Contractual Obligation, Due in Second Year 6,700,000    
Hydraulic Fracturing
      
Commitments And Contingencies Disclosure [Line Items]      
Contractual Obligation, Due in Next Twelve Months 24,000,000    
Contractual Obligation, Due in Second Year 12,000,000    
Seismic
      
Commitments And Contingencies Disclosure [Line Items]      
Contractual Obligation, Due in Next Twelve Months 10,600,000    
Contractual Obligation, Due in Second Year $ 838,000    
Natural Gas | Minimum
      
Commitments And Contingencies Disclosure [Line Items]      
Delivery commitments contingent upon pipeline construction or modification 40,000    
Natural Gas | Maximum
      
Commitments And Contingencies Disclosure [Line Items]      
Delivery commitments contingent upon pipeline construction or modification 200,000    
Ethane | Minimum
      
Commitments And Contingencies Disclosure [Line Items]      
Delivery commitments contingent upon pipeline construction or modification in bbl/day 10,000    
Ethane | Maximum
      
Commitments And Contingencies Disclosure [Line Items]      
Delivery commitments contingent upon pipeline construction or modification in bbl/day 20,000