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Properties and Equipment (Details 2) (USD $)
 12 Months Ended 1 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2014
Properties and Equipment        
Impairment of oil and gas properties $ 771,037,000us-gaap_ImpairmentOfOilAndGasProperties $ 0us-gaap_ImpairmentOfOilAndGasProperties $ 0us-gaap_ImpairmentOfOilAndGasProperties  
Oil and Gas Properties | Significant Unobservable Inputs (Level 3)        
Properties and Equipment        
Capital rate       10.00%us-gaap_FairValueInputsCapRate
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_OilAndGasPropertiesMember
East And South Texas        
Properties and Equipment        
Fair value of oil and gas properties subject to impairment $ 86,500,000cog_OilAndGasPropertySuccessfulEffortMethodSubjectToImpairmentFairValue
/ us-gaap_StatementGeographicalAxis
= cog_EastAndSouthTexasMember		     86,500,000cog_OilAndGasPropertySuccessfulEffortMethodSubjectToImpairmentFairValue
/ us-gaap_StatementGeographicalAxis
= cog_EastAndSouthTexasMember