Represents the percentage of participation interest acquired during the period.

No definition available.

Name:	kos_AcquiredParticipationInterestPercentage
Namespace Prefix:	kos_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the gross amount of spend per well on two appraisal wells, whereby, a third party will pay a disproportionate amount of their drilling costs.

+ References

No definition available.

+ Details

Name:	kos_AmountOfAppraisalWellCostsPaidByThirdParty
Namespace Prefix:	kos_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the gross amount spent on an exploration well, whereby, a third party will pay a disproportionate amount of their costs.

+ References

No definition available.

+ Details

Name:	kos_AmountOfExplorationWellCostsPaidByThirdParty
Namespace Prefix:	kos_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the gross amount of spend on the first exploration well in each block, whereby, a third party will pay our share of drilling costs.

+ References

No definition available.

+ Details

Name:	kos_AmountOfFirstExplorationWellCostsToBePaidByThirdParty
Namespace Prefix:	kos_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the amount of our costs to be paid for by a third party, which will be applied to our share of future costs.

+ References

No definition available.

+ Details

Name:	kos_AmountOfOurFutureCostsToBeReceived
Namespace Prefix:	kos_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the amount of past costs received from the third party for farming into the block.

+ References

No definition available.

+ Details

Name:	kos_AmountOfPastCostsReceived
Namespace Prefix:	kos_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the gross amount of spend on the second exploration well in each block, whereby, a third party will pay a disproportionate amount of their drilling costs.

+ References

No definition available.

+ Details

Name:	kos_AmountOfSecondExplorationWellCostsToBePaidByThirdParty
Namespace Prefix:	kos_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the gross amount of seismic costs spent, whereby, a third party will pay a disproportionate amount of their costs.

+ References

No definition available.

+ Details

Name:	kos_AmountOfSeismicCostsPaidByThirdParty
Namespace Prefix:	kos_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Number of contingent exploration wells.

+ References

No definition available.

+ Details

Name:	kos_ExplorationWellsNumberContingent
Namespace Prefix:	kos_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the increase (decrease) in exploration costs incurred during the reporting period.

+ References

No definition available.

+ Details

Name:	kos_IncreaseDecreaseInExplorationExpense
Namespace Prefix:	kos_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the increase (decrease) in general and administrative expense incurred during the reporting period.

+ References

No definition available.

+ Details

Name:	kos_IncreaseDecreaseInGeneralAndAdministrativeExpense
Namespace Prefix:	kos_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the amount of investment cap on the first exploration well.

+ References

No definition available.

+ Details

Name:	kos_InvestmentCapAmount
Namespace Prefix:	kos_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the maximum gross amount to be incurred per contingent exploration well, whereby, Kosmos will pay all of a third party's cost

+ References

No definition available.

+ Details

Name:	kos_MaximumAmountOfContingentExplorationWellCost
Namespace Prefix:	kos_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of appraisal wells for which a third party will pay a disproportionate amount of their drilling costs.

+ References

No definition available.

+ Details

Name:	kos_NumberOfAppraisalWellsForWhichThirdPartyPaysDisproportionateShareOfCosts
Namespace Prefix:	kos_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of blocks covered by farm-out agreements.

+ References

No definition available.

+ Details

Name:	kos_NumberOfBlocksCoveredByFarmOutAgreements
Namespace Prefix:	kos_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents number of exploration wells in each block for which our share of costs will be paid for by a third party.

+ References

No definition available.

+ Details

Name:	kos_NumberOfExplorationWellsForWhichOurCostIsPaid
Namespace Prefix:	kos_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of exploration wells for which a third party will pay a disproportionate amount of their drilling costs.

+ References

No definition available.

+ Details

Name:	kos_NumberOfExplorationWellsForWhichThirdPartyPaysDisproportionateShareOfCosts
Namespace Prefix:	kos_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of farm-out agreements.

+ References

No definition available.

+ Details

Name:	kos_NumberOfFarmOutAgreements
Namespace Prefix:	kos_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the participating interest percentage.

+ References

No definition available.

+ Details

Name:	kos_ParticipatingInterestPercentage
Namespace Prefix:	kos_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the participating interest percentage should Kosmos elect to pay all of the third party's cost on a third contingent exploration or appraisal well.

+ References

No definition available.

+ Details

Name:	kos_ParticipatingInterestPercentageAfterAdditionalWell
Namespace Prefix:	kos_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of costs of the first exploration well on each block to be funded.

+ References

No definition available.

+ Details

Name:	kos_PercentageOfCostsOfFirstExplorationWellOnEachBlockToBeFunded
Namespace Prefix:	kos_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents percentage of third party's share of drilling costs to be paid in the event of drilling a second exploration well in each block.

+ References

No definition available.

+ Details

Name:	kos_PercentageOfThirdPartysShareOfCostsToBePaidInEventOfDrillingSecondExplorationWell
Namespace Prefix:	kos_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of third party's share of seismic and drilling costs to be paid in the block.

+ References

No definition available.

+ Details

Name:	kos_PercentageOfThirdPartysShareOfDrillingAndSeismicCosts
Namespace Prefix:	kos_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of third party's share of drilling costs to be paid on up to two appraisal wells in the block.

+ References

No definition available.

+ Details

Name:	kos_PercentageOfThirdPartysShareOfDrillingCostsForAppraisalWells
Namespace Prefix:	kos_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	kos_PropertyPlantAndEquipmentAcquisitionsAndDivestituresLineItems
Namespace Prefix:	kos_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of gain (loss) on sale or disposal of oil and gas property or timber property.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

+ Details

Name:	us-gaap_GainLossOnSaleOfProperty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow to dispose of long-lived, physical assets and mineral interests in oil and gas properties used for normal oil and gas operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 12

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromSaleOfOilAndGasPropertyAndEquipment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=kos_AntrimEnergyIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=kos_BPPlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=kos_CairnEnergyPLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=kos_ChevronGlobalEnergyIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=kos_EuropaOilAndGasHoldingsPlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=kos_SocitMauritanienneDesHydrocarburesEtDePatrimoineMinierMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=kos_TimisCorporationLimitedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	kos_OilAndGasAgreementAxis=kos_EssaouriaOffshorePetroleumAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	kos_OilAndGasAgreementAxis=kos_FarmOutAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	kos_OilAndGasAgreementAxis=kos_FoumAssakaOffshorePetroleumAgreementMember
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Acquisitions and Divestitures (Details) (USD $)	12 Months Ended	1 Months Ended				3 Months Ended	1 Months Ended	3 Months Ended		1 Months Ended
Acquisitions and Divestitures (Details) (USD $)	Dec. 31, 2014	Nov. 30, 2012	Feb. 23, 2015	Jan. 31, 2013	Aug. 31, 2013	Dec. 31, 2012	Apr. 30, 2013	Mar. 31, 2014 item agreement	Jun. 30, 2014	Aug. 31, 2014 site
Acquisitions and Divestitures
Proceeds on sale of assets	$ 58,315,000
Gain on sale of assets	23,769,000us-gaap_GainLossOnSaleOfProperty
Farm-out agreements \| Block 42 and Block 45
Acquisitions and Divestitures
Participating interests (as a percent)		50.00%
Farm-out agreements \| Essaouira Offshore Block
Acquisitions and Divestitures
Participating interests (as a percent)	30.00%
Farm-out agreements \| Foum Assaka Offshore Block
Acquisitions and Divestitures
Participating interests (as a percent)	29.90%
Farm-out agreements \| Tarhazoute Offshore Block
Acquisitions and Divestitures
Participating interests (as a percent)	30.00%
Farm-out agreements \| Cap Boujdour Offshore block
Acquisitions and Divestitures
Participating interests (as a percent)	55.00%
Farm-out agreements \| Block C8
Acquisitions and Divestitures
Participating interests (as a percent)			60.00%
Farm-out agreements \| Block C12
Acquisitions and Divestitures
Participating interests (as a percent)			60.00%
Farm-out agreements \| Block C13
Acquisitions and Divestitures
Participating interests (as a percent)			60.00%
Essaouria Offshore Petroleum Agreement \| Essaouira Offshore Block
Acquisitions and Divestitures
Participation interest acquired (as a percent)				37.50%
Foum Assaka Offshore Petroleum Agreement \| Foum Assaka Offshore Block
Acquisitions and Divestitures
Participation interest acquired (as a percent)					18.80%
Chevron \| Farm-out agreements \| Block 42 and Block 45
Acquisitions and Divestitures
Reimbursement of shared costs previously incurred						23,700,000
Reduction in exploration expense						22,700,000
Reduction in general and administrative expense						1,000,000
Participation interest acquired (as a percent)		50.00%
Chevron \| Farm-out agreements \| Block C8, Block 12 and Block 13
Acquisitions and Divestitures
Number of exploration wells for which a third party will pay a disproportionate amount			1
Participation interest acquired (as a percent)			30.00%
Chevron \| Farm-out agreements \| Block C8
Acquisitions and Divestitures
Participating interests (as a percent)			30.00%
Chevron \| Farm-out agreements \| Block C12
Acquisitions and Divestitures
Participating interests (as a percent)			30.00%
Chevron \| Farm-out agreements \| Block C13
Acquisitions and Divestitures
Participating interests (as a percent)			30.00%
Antrim Energy Inc. \| Farm-in agreement \| Licensing Option 11/5
Acquisitions and Divestitures
Participation interest acquired (as a percent)							75.00%
Europa Oil & Gas (Holdings) plc \| Farm-in agreement \| Licensing Option 11/7
Acquisitions and Divestitures
Participation interest acquired (as a percent)							85.00%
Percentage of costs of the first exploration well to be funded							100.00%
Europa Oil & Gas (Holdings) plc \| Farm-in agreement \| Licensing Option 11/7 \| Maximum
Acquisitions and Divestitures
Investment cap amount							90,000,000
Europa Oil & Gas (Holdings) plc \| Farm-in agreement \| Licensing Option 11/8
Acquisitions and Divestitures
Participation interest acquired (as a percent)							85.00%
Percentage of costs of the first exploration well to be funded							100.00%
Europa Oil & Gas (Holdings) plc \| Farm-in agreement \| Licensing Option 11/8 \| Maximum
Acquisitions and Divestitures
Investment cap amount							110,000,000
BP \| Farm-out agreements \| Essaouira Offshore, Foum Assaka Offshore and Tarhazoute Offshore blocks
Acquisitions and Divestitures
Number of farm-out agreements								3
Number of blocks covered by farm-out agreements								3
Proceeds on sale of assets								56,900,000
Gain on sale of assets	23,800,000
Number of exploration wells in each block for which our share of costs will be paid for by a third party								1
Percentage of third party's share of drilling costs to be paid in the event of drilling a second exploration well in each block								150.00%
BP \| Farm-out agreements \| Essaouira Offshore, Foum Assaka Offshore and Tarhazoute Offshore blocks \| Maximum
Acquisitions and Divestitures
Spending per well by third party for first exploration well								120,000,000
Spending per well by third party in the event of drilling a second exploration well								120,000,000
Cairn \| Farm-out agreements
Acquisitions and Divestitures
Number of exploration wells for which a third party will pay a disproportionate amount								1
Cairn \| Farm-out agreements \| Cap Boujdour Offshore block
Acquisitions and Divestitures
Reimbursement of shared costs previously incurred									1,500,000
Participation interest acquired (as a percent)								20.00%
Percentage of third party's share of seismic and drilling costs								150.00%
Percentage of third party's share of drilling costs for two appraisal wells								200.00%
Number of appraisal wells for which a third party will pay a disproportionate amount								2
Amount of our future costs to be paid for by third party								12,300,000
Cairn \| Farm-out agreements \| Cap Boujdour Offshore block \| Maximum
Acquisitions and Divestitures
Spending by third party for seismic costs								25,000,000
Spending by third party for an exploration well								$ 100,000,000
Spending per well by third party for each appraisal well								100,000,000
Timis Corporation Limited \| Farm-in agreement \| Cayar Offshore Profond and Saint Louis Offshore Profond blocks
Acquisitions and Divestitures
Participation interest acquired (as a percent)										60.00%
Maximum cost per contingent exploration well										120,000,000
Number of contingent exploration wells										2
Participating interest for carrying the full cost of third contingent exploration or appraisal well (as a percent)										65.00%
SMHPM \| Farm-out agreements \| Block C8
Acquisitions and Divestitures
Participating interests (as a percent)			10.00%
SMHPM \| Farm-out agreements \| Block C12
Acquisitions and Divestitures
Participating interests (as a percent)			10.00%
SMHPM \| Farm-out agreements \| Block C13
Acquisitions and Divestitures
Participating interests (as a percent)			10.00%