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Joint Interest Billings (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Mar. 31, 2015
Joint interest billings    
Long-term receivables - joint interest billings 14,174us-gaap_OilAndGasJointInterestBillingReceivablesNoncurrent $ 18,321us-gaap_OilAndGasJointInterestBillingReceivablesNoncurrent
GNPC    
Joint interest billings    
Long-term receivables - joint interest billings 14,200us-gaap_OilAndGasJointInterestBillingReceivablesNoncurrent
/ us-gaap_CounterpartyNameAxis
= kos_GhanaNationalPetroleumCorporationMember		 $ 18,300us-gaap_OilAndGasJointInterestBillingReceivablesNoncurrent
/ us-gaap_CounterpartyNameAxis
= kos_GhanaNationalPetroleumCorporationMember
TEN Discoveries | GNPC    
Joint interest billings    
GNPC's paying interest (as a percent) 5.00%kos_PayingInterestPercentage
/ dei_LegalEntityAxis
= kos_GhanaNationalPetroleumCorporationMember
/ kos_OilAndGasDiscoveriesAxis
= kos_TweneboaEnyenraAndNtommeDiscoveriesMember