| Cover Document | Nov. 09, 2020 |
| Cover [Abstract] | |
| Entity Address, Address Description | 8176 Park Lane |
| Entity Address, City or Town | Dallas, |
| Entity Address, State or Province | TX |
| Document Type | 8-K |
| Document Period End Date | Nov. 9, 2020 |
| Entity Registrant Name | KOSMOS ENERGY LTD. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-35167 |
| Entity Tax Identification Number | 98-0686001 |
| Entity Address, Postal Zip Code | 75231 |
| Title of 12(b) Security | Common Stock $0.01 par value |
| Trading Symbol | KOS |
| Security Exchange Name | NYSE |
| City Area Code | 214 |
| Local Phone Number | 445 9600 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
| Entity Central Index Key | 0001509991 |
