Represents the percentage of participation interest acquired during the period.

No definition available.

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Data Type:	num:percentItemType
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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

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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

- 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

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

- Details

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

- Details

Name:	kos_OilAndGasAgreementAxis=kos_FarmOutAgreementMember
Namespace Prefix:
Data Type:	na
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Acquisitions and Divestitures (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		1 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015
Acquisitions and Divestitures
Proceeds on sale of assets		$ 34,581
Gain on sale of assets	22,751us-gaap_GainLossOnSaleOfProperty	23,769us-gaap_GainLossOnSaleOfProperty
Farm-in agreement \| Camarao, Ameijoa, Mexilhao and Ostra blocks
Acquisitions and Divestitures
Participating interests (as a percent)			31.00%
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%
Chevron \| Farm-out agreements \| Block C8, Block 12 and Block 13
Acquisitions and Divestitures
Proceeds on sale of assets			29,700
Gain on sale of assets			22,800
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%
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%