Kosmos Energy (KOS) 10-Q 5 Nov 13 2013 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2013	Oct. 28, 2013
Document and Entity Information	'	'
Entity Registrant Name	'Kosmos Energy Ltd.	'
Entity Central Index Key	'0001509991	'
Document Type	'10-Q	'
Document Period End Date	30-Sep-13	'
Amendment Flag	'false	'
Current Fiscal Year End Date	'--12-31	'
Entity Current Reporting Status	'Yes	'
Entity Filer Category	'Large Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	387,559,187
Document Fiscal Year Focus	'2013	'
Document Fiscal Period Focus	'Q3	'

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$440,267	$515,164
Restricted cash	19,377	21,341
Receivables:	'	'
Joint interest billings	71,591	21,539
Oil sales	113,067	108,995
Other	4,995	3,682
Inventories	33,118	33,281
Prepaid expenses and other	11,596	10,470
Current deferred tax assets	14,515	34,585
Derivatives	917	1,061
Total current assets	709,443	750,118
Property and equipment:	'	'
Oil and gas properties, net	1,486,224	1,510,312
Other property, net	15,490	15,450
Property and equipment, net	1,501,714	1,525,762
Other assets:	'	'
Restricted cash	24,634	29,884
Deferred financing costs, net of accumulated amortization of $22,191 and $13,922 at September 30, 2013 and December 31, 2012, respectively	42,897	50,214
Long-term deferred tax assets	14,808	10,145
Derivatives	1,583	'
Total assets	2,295,079	2,366,123
Current liabilities:	'	'
Accounts payable	98,818	128,855
Accrued liabilities	115,866	41,021
Derivatives	9,458	20,377
Total current liabilities	224,142	190,253
Long-term liabilities:	'	'
Long-term debt	900,000	1,000,000
Derivatives	1,335	3,226
Asset retirement obligations	35,226	27,484
Deferred tax liability	145,193	104,137
Other long-term liabilities	18,886	12,117
Total long-term liabilities	1,100,640	1,146,964
Shareholders' equity:	'	'
Preference shares, $0.01 par value; 200,000,000 authorized shares; zero issued at September 30, 2013 and December 31, 2012	'	'
Common shares, $0.01 par value; 2,000,000,000 authorized shares; 391,956,419 and 391,423,703 issued at September 30, 2013 and December 31, 2012, respectively	3,920	3,914
Additional paid-in capital	1,763,227	1,712,880
Accumulated deficit	-778,386	-683,176
Accumulated other comprehensive income	2,563	3,685
Treasury stock, at cost, 4,397,232 and 2,731,941 shares at September 30, 2013 and December 31, 2012, respectively	-21,027	-8,397
Total shareholders' equity	970,297	1,028,906
Total liabilities and shareholders' equity	$2,295,079	$2,366,123

CONSOLIDATED_BALANCE_SHEETS_Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, except Share data, unless otherwise specified
CONSOLIDATED BALANCE SHEETS	'	'
Deferred financing costs, accumulated amortization (in dollars)	$22,191	$13,922
Preference shares, par value (in dollars per share)	$0.01	$0.01
Preference shares, authorized shares	200,000,000	200,000,000
Preference shares, issued shares	0	0
Common shares, par value (in dollars per share)	$0.01	$0.01
Common shares, authorized shares	2,000,000,000	2,000,000,000
Common shares, issued shares	391,956,419	391,423,703
Treasury stock, shares	4,397,232	2,731,941

CONSOLIDATED_STATEMENTS_OF_OPE

CONSOLIDATED STATEMENTS OF OPERATIONS (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues and other income:	'	'	'	'
Oil and gas revenue	$215,169	$222,375	$636,648	$450,360
Interest income	77	137	191	1,165
Other income	133	725	708	930
Total revenues and other income	215,379	223,237	637,547	452,455
Costs and expenses:	'	'	'	'
Oil and gas production	32,576	44,873	79,651	71,791
Exploration expenses	78,038	38,127	194,384	96,134
General and administrative	35,646	39,898	118,787	112,558
Depletion and depreciation	58,367	63,794	175,578	128,442
Amortization-deferred financing costs	2,786	2,194	8,269	6,582
Interest expense	8,781	20,213	27,789	43,717
Derivatives, net	7,585	24,529	386	26,407
Other expenses, net	1,864	-64	3,345	728
Total costs and expenses	225,643	233,564	608,189	486,359
Income (loss) before income taxes	-10,264	-10,327	29,358	-33,904
Income tax expense	34,224	25,923	124,568	64,730
Net loss	($44,488)	($36,250)	($95,210)	($98,634)
Net loss per share:	'	'	'	'
Basic (in dollars per share)	($0.12)	($0.10)	($0.25)	($0.27)
Diluted (in dollars per share)	($0.12)	($0.10)	($0.25)	($0.27)
Weighted average number of shares used to compute net loss per share:	'	'	'	'
Basic (in shares)	377,654	373,448	376,509	371,140
Diluted (in shares)	377,654	373,448	376,509	371,140

CONSOLIDATED_STATEMENTS_OF_COM

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS	'	'	'	'
Net loss	($44,488)	($36,250)	($95,210)	($98,634)
Other comprehensive income (loss):	'	'	'	'
Reclassification adjustments for derivative (gains) losses included in net loss	-405	-133	-1,122	295
Other comprehensive income (loss)	-405	-133	-1,122	295
Comprehensive loss	($44,893)	($36,383)	($96,332)	($98,339)

CONSOLIDATED_STATEMENTS_OF_SHA

CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (USD $)	Total	Common Shares	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income	Treasury Stock
In Thousands, unless otherwise specified
Balance at Dec. 31, 2012	$1,028,906	$3,914	$1,712,880	($683,176)	$3,685	($8,397)
Balance (in shares) at Dec. 31, 2012	'	391,424	'	'	'	'
Increase (Decrease) in Shareholders' Equity	'	'	'	'	'	'
Equity-based compensation	50,792	'	50,792	'	'	'
Derivatives, net	-1,122	'	'	'	-1,122	'
Restricted stock awards and units	'	6	-6	'	'	'
Restricted stock awards and units (in shares)	'	532	'	'	'	'
Restricted stock forfeitures	'	'	6	'	'	-6
Purchase of treasury stock	-13,069	'	-445	'	'	-12,624
Net loss	-95,210	'	'	-95,210	'	'
Balance at Sep. 30, 2013	$970,297	$3,920	$1,763,227	($778,386)	$2,563	($21,027)
Balance (in shares) at Sep. 30, 2013	'	391,956	'	'	'	'

CONSOLIDATED_STATEMENTS_OF_CAS

CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Operating activities	'	'
Net loss	($95,210)	($98,634)
Adjustments to reconcile net loss to net cash provided by operating activities:	'	'
Depletion, depreciation and amortization	183,847	135,024
Deferred income taxes	62,757	51,867
Unsuccessful well costs	98,912	19,357
Change in fair value of derivatives	4,752	13,847
Cash settlements on derivatives	-18,658	-18,755
Equity-based compensation	50,792	58,215
Other	4,468	7,739
Changes in assets and liabilities:	'	'
(Increase) decrease in receivables	-56,725	89,102
Increase in inventories	-2,419	-7,812
(Increase) decrease in prepaid expenses and other	-1,126	4,112
Decrease in accounts payable	-30,037	-127,025
Increase in accrued liabilities	79,996	23,073
Net cash provided by operating activities	281,349	150,110
Investing activities	'	'
Oil and gas assets	-244,452	-272,681
Other property	-3,712	-9,030
Restricted cash	7,214	-23,089
Net cash used in investing activities	-240,950	-304,800
Financing activities	'	'
Payment on long-term debt	-100,000	-110,000
Purchase of treasury stock	-13,069	-8,378
Deferred financing costs	-2,227	-374
Net cash used in financing activities	-115,296	-118,752
Net decrease in cash and cash equivalents	-74,897	-273,442
Cash and cash equivalents at beginning of period	515,164	673,092
Cash and cash equivalents at end of period	440,267	399,650
Cash paid for:	'	'
Interest	27,046	30,247
Income taxes	$49,716	$16,620

Organization

Organization	9 Months Ended
	Sep. 30, 2013
Organization	'
Organization	'
	1. Organization
	Kosmos Energy Ltd. was incorporated pursuant to the laws of Bermuda in January 2011 to become a holding company for Kosmos Energy Holdings. Kosmos Energy Holdings is a privately held Cayman Islands company that was formed in March 2004. As a holding company, Kosmos Energy Ltd.’s management operations are conducted through a wholly owned subsidiary, Kosmos Energy, LLC. The terms “Kosmos,” the “Company,” “we,” “us,” “our,” “ours,” and similar terms refer to Kosmos Energy Ltd. and its wholly owned subsidiaries, unless the context indicates otherwise.
	We are a leading independent oil and gas exploration and production company focused on frontier and emerging areas along the Atlantic Margin. Our asset portfolio includes existing production and other major project developments offshore Ghana, as well as exploration licenses with significant hydrocarbon potential offshore Ireland, Mauritania, Morocco (including Western Sahara) and Suriname. Kosmos is listed on the New York Stock Exchange and is traded under the ticker symbol KOS.
	We have one reportable segment, which is the exploration and production of oil and natural gas. Substantially all of our long-lived assets and product sales are currently related to production located offshore Ghana.

Accounting_Policies

Accounting Policies	9 Months Ended
	Sep. 30, 2013
Accounting Policies	'
Accounting Policies	'
	2. Accounting Policies
	General
	The interim-period financial information presented in the consolidated financial statements included in this report is unaudited and, in the opinion of management, includes all adjustments of a normal recurring nature necessary to present fairly the consolidated financial position as of September 30, 2013, the changes in the consolidated statements of shareholders’ equity for the nine months ended September 30, 2013, the consolidated results of operations for the three and nine months ended September 30, 2013 and 2012, and consolidated cash flows for the nine months ended September 30, 2013 and 2012. The results of the interim periods shown in this report are not necessarily indicative of the final results to be expected for the full year. The consolidated financial statements were prepared in accordance with the requirements of the Securities and Exchange Commission (“SEC”) for interim reporting. As permitted under those rules, certain notes or other financial information that are normally required by Generally Accepted Accounting Principles (“GAAP”) have been condensed or omitted from these interim consolidated financial statements. These consolidated financial statements and the accompanying notes should be read in conjunction with our audited consolidated financial statements for the year ended December 31, 2012, included in our annual report on Form 10-K.
	Reclassifications
	Certain prior period amounts have been reclassified to conform with the current year presentation. Such reclassifications had no impact on our reported net loss, current assets, total assets, current liabilities, total liabilities or shareholders’ equity.
	Restricted Cash
	In accordance with our commercial debt facility, we are required to maintain a restricted cash balance that is sufficient to meet the payment of interest and fees for the next six-month period. As of September 30, 2013 and December 31, 2012, we had $19.4 million and $21.3 million, respectively, in current restricted cash to meet this requirement. In addition, in accordance with certain of our petroleum contracts, we have posted letters of credit related to performance guarantees for our minimum work obligations. These letters of credit are cash collateralized in accounts held by us and as such are classified as restricted cash. Upon completion of the minimum work obligations and/or entering into the next phase of the petroleum contract, the requirement to post letters of credit will be satisfied and the cash collateral will be released. As of September 30, 2013 and December 31, 2012, we had $24.6 million and $29.9 million, respectively, of long-term restricted cash used to cash collateralize performance guarantees related to our petroleum contracts.
	Inventories
	Inventories consisted of $32.3 million and $33.1 million of materials and supplies and $0.8 million and $0.2 million of hydrocarbons as of September 30, 2013 and December 31, 2012, respectively. The Company’s materials and supplies inventory primarily consists of casing and wellheads and is stated at the lower of cost, using the weighted average cost method, or market.
	Hydrocarbon inventory is carried at the lower of cost, using the weighted average cost method, or market. Hydrocarbon inventory costs include expenditures and other charges directly and indirectly incurred in bringing the inventory to its existing condition. Selling expenses and general and administrative expenses are reported as period costs and excluded from inventory costs.
	Variable Interest Entity
	Our wholly owned subsidiary, Kosmos Energy Finance International, is a variable interest entity (“VIE”). The Company is the primary beneficiary of this VIE, which is consolidated in these financial statements.
	Kosmos Energy Finance International’s following assets and liabilities are shown separately on the face of the consolidated balance sheet as of September 30, 2013 and December 31, 2012: current restricted cash; long-term derivatives assets; long-term debt; and current and long-term derivatives liabilities. At September 30, 2013, Kosmos Energy Finance International had $36.9 million in cash and cash equivalents; $0.4 million in prepaid expenses and other; $0.9 million current derivative assets; $36.2 million deferred financing costs, net; $1.5 million in accrued liabilities and $7.6 million in other long-term liabilities, which are included in the amounts shown on the face of the consolidated balance sheet. At December 31, 2012, Kosmos Energy Finance International had $118.8 million in cash and cash equivalents; $0.2 million in prepaid expenses and other; $42.2 million deferred financing costs, net; $0.5 million in accrued liabilities and $6.6 million in other long-term liabilities, which are included in the amounts shown on the face of the consolidated balance sheet.

Property_and_Equipment

Property and Equipment	9 Months Ended
	Sep. 30, 2013
Property and Equipment	'
Property and Equipment	'
	3. Property and Equipment
	Property and equipment is stated at cost and consisted of the following:
		September 30,			December 31,
		2013			2012
		(In thousands)
	Oil and gas properties:
	Proved properties	$	767,288		$	682,276
	Unproved properties	489,874			454,391
	Support equipment and facilities	712,415			687,835
	Total oil and gas properties	1,969,577			1,824,502
	Less: accumulated depletion	(483,353		)	(314,190		)
	Oil and gas properties, net	1,486,224			1,510,312
	Other property	30,978			27,316
	Less: accumulated depreciation	(15,488		)	(11,866		)
	Other property, net	15,490			15,450
	Property and equipment, net	$	1,501,714		$	1,525,762
	We recorded depletion expense of $56.1 million and $61.9 million for the three months ended September 30, 2013 and 2012, respectively and $169.2 million and $123.3 million for the nine months ended September 30, 2013 and 2012, respectively.

Suspended_Well_Costs

Suspended Well Costs	9 Months Ended
	Sep. 30, 2013
Suspended Well Costs	'
Suspended Well Costs	'
	4. Suspended Well Costs
	The following table reflects the Company’s capitalized exploratory well costs on completed wells as of and during the nine months ended September 30, 2013. The table excludes $69.8 million in costs that were capitalized and subsequently expensed during the same period.
		Nine Months
		Ended
		September 30,
		2013
		(In thousands)
	Beginning balance	$	372,492
	Additions to capitalized exploratory well costs pending the determination of proved reserves	30,415
	Reclassification due to determination of proved reserves	—
	Capitalized exploratory well costs charged to expense	(26,997		)
	Ending balance	$	375,910
	The following table provides an aging of capitalized exploratory well costs based on the date drilling was completed and the number of projects for which exploratory well costs have been capitalized for more than one year since the completion of drilling:
		September 30, 2013			December 31, 2012
		(In thousands, except well counts)
	Exploratory well costs capitalized for a period of one year or less	$	11,470		$	106,635
	Exploratory well costs capitalized for a period one to two years	228,842			179,933
	Exploratory well costs capitalized for a period three to four years	135,598			85,924
	Ending balance	$	375,910		$	372,492
	Number of projects that have exploratory well costs that have been capitalized for a period greater than one year	8			7
	As of September 30, 2013, the projects with exploratory well costs capitalized for more than one year since the completion of drilling are related to the Mahogany, Teak-1, Teak-2 and Akasa discoveries in the West Cape Three Points (“WCTP”) Block and the Tweneboa, Enyenra, Ntomme and Wawa discoveries in the Deepwater Tano (“DT”) Block, which are all in Ghana.
	Mahogany—Mahogany, a combined area covering parts of the Mahogany East discovery and the Mahogany Deep discovery, was declared commercial in September 2010, and a PoD was submitted to Ghana’s Ministry of Energy as of May 2, 2011. In a letter dated May 16, 2011, the Ministry of Energy did not approve the PoD and requested that the WCTP Block partners take certain steps regarding notifications of discovery and commerciality; and requested other information. The WCTP Block partners believe the combined submission was proper and have held meetings with Ghana National Petroleum Corporation (“GNPC”) which resolved issues relating to the PoD work program. From May 2011, the Ministry of Energy, GNPC and the WCTP Block partners continued working to resolve other differences; however, the WCTP Petroleum Agreement (“PA”) contains specific timelines for PoD approval and discussions, which expired at the end of June 2011. On June 30, 2011, we, as Operator of the WCTP Block and on behalf of the WCTP Block partners, delivered a Notice of Dispute to the Ministry of Energy and GNPC as provided under the WCTP PA, which is the initial step in triggering the formal dispute resolution process under the WCTP PA with the government of Ghana regarding approval of the Mahogany PoD. This Notice of Dispute establishes a process for negotiation and consultation for a period of 30 days (or longer if mutually agreed) among senior representatives from the Ministry of Energy, GNPC and the WCTP Block partners to resolve the matter. We and the WCTP Block partners are in discussions with the Ministry of Energy and GNPC to resolve differences on the PoD.
	Teak-1 Discovery—Two appraisal wells have been drilled. Following additional appraisal and evaluation, a decision regarding commerciality of the Teak-1 discovery is expected to be made by the WCTP Block partners in 2014. Within six months of such a declaration, a PoD would be prepared and submitted to Ghana’s Ministry of Energy, as required under the WCTP PA.
	Teak-2 Discovery—We have performed a gauge installation on the well and are reprocessing seismic data. Following additional appraisal and evaluation, a decision regarding commerciality of the Teak-2 discovery is expected to be made by the WCTP Block partners in 2014. Within six months of such a declaration, a PoD would be prepared and submitted to Ghana’s Ministry of Energy, as required under the WCTP PA.
	Akasa Discovery—We have performed a drill stem test and gauge installation on the discovery well and are currently drilling the Akasa-2A appraisal well (see Note 13—Subsequent Events). Following additional appraisal and evaluation, a decision regarding commerciality of the Akasa discovery is expected to be made by the WCTP Block partners in 2014. Within six months of such a declaration, a PoD would be prepared and submitted to Ghana’s Ministry of Energy, as required under the WCTP PA.
	Tweneboa, Enyenra and Ntomme (“TEN”) Discoveries—In May 2013, the government of Ghana approved the PoD over the TEN discoveries. Development of TEN will include the drilling and completion of up to 24 development wells, half of the wells are designed as producers and the remainder are for water and gas injection to support ultimate field recoveries. The TEN project is expected to deliver first oil in 2016. The costs associated with the TEN development will remain as unproved property pending the determination of whether the discoveries are associated with proved reserves.
	Wawa Discovery—We are currently reprocessing seismic data and plan to acquire a high resolution seismic survey over the discovery area in 2014. Following additional evaluation and potential appraisal activities, a decision regarding commerciality of the Wawa discovery is expected to be made by the DT Block partners in 2014. Within six months of such declaration, a PoD would be prepared and submitted to Ghana’s Ministry of Energy, as required under the DT PA.

Accounts_Payable_and_Accrued_L

Accounts Payable and Accrued Liabilities	9 Months Ended
	Sep. 30, 2013
Accounts Payable and Accrued Liabilities	'
Accounts Payable and Accrued Liabilities	'
	5. Accounts Payable and Accrued Liabilities
	At September 30, 2013 and December 31, 2012, accounts payable of $98.8 million and $128.9 million, respectively, were recorded for invoices received but not paid. Accrued liabilities consisted of the following:
		September 30,		December 31,
		2013		2012
		(In thousands)
	Accrued liabilities:
	Accrued exploration, development and production	$	65,561	$	20,616
	Accrued general and administrative expenses	14,896		5,089
	Accrued taxes other than income	15,667		11,124
	Accrued derivative settlements	1,465		—
	Income taxes	18,277		4,192
		$	115,866	$	41,021

Debt

Debt	9 Months Ended
	Sep. 30, 2013
Debt	'
Debt	'
	6. Debt
	Facility
	In March 2011, the Company secured a $2.0 billion commercial debt facility (the “Facility”) from a number of financial institutions and extinguished the then existing commercial debt facilities. The Facility was syndicated to certain participants of the existing facilities, as well as new participants. The Facility supports our oil and gas exploration, appraisal and development programs and corporate activities. As part of an amendment in November 2012, the total commitments for the Facility were reduced to $1.5 billion.
	The Facility provides a revolving-credit and letter of credit facility. The availability period for the revolving-credit facility, as amended in April 2013, expires on December 15, 2014 and the letter of credit sublimit expires on the final maturity date. The available facility amount is subject to borrowing base constraints and, beginning on December 15, 2014, outstanding borrowings will also be constrained by an amortization schedule. The final maturity date is March 29, 2018.
	In September 2013, as part of the normal borrowing base determination process, the availability under the facility was reduced by $89.6 million to $1.2 billion. As of September 30, 2013, borrowings under the Facility totaled $900.0 million, the undrawn availability under the Facility was $309.5 million, and there were no letters of credit drawn under the facility.
	Corporate Revolver
	In November 2012, we secured a revolving credit facility (the “Corporate Revolver”). In April 2013, the availability under the Corporate Revolver was increased from $260.0 million to $300.0 million due to additional commitments received from existing and new financial institutions. As of September 30, 2013, there were no borrowings outstanding under the Corporate Revolver and the undrawn availability under the Corporate Revolver was $300.0 million.
	Revolving Letter of Credit Facility
	In July 2013, we entered into a revolving letter of credit facility agreement (“LC Facility”). The size of the LC Facility is $100.0 million, with additional commitments up to $50.0 million being available if the existing lender increases its commitment or if commitments from new financial institutions are added. The LC Facility provides that we maintain cash collateral in an amount equal to at least 75% of all outstanding letters of credit under the LC Facility, provided that during the period of any breach of certain financial covenants, the required cash collateral amount shall increase to 100%. The fees associated with outstanding letters of credit issued will be 0.5% per annum. The LC Facility has an availability period which expires on June 1, 2016. We may voluntarily cancel any commitments available under the LC Facility at any time. As of September 30, 2013, there were four outstanding letters of credit totaling $29.0 million under the LC Facility.
	At September 30, 2013, the estimated repayments of debt during the five fiscal year periods and thereafter are as follows:
		Payments Due by Year
		2013(1)		2014		2015		2016		2017		Thereafter
		(In thousands)
	Facility(2)	$	—	$	—	$	346,693	$	149,428	$	292,768	$	111,111
	(1)                                 Represents payments for the period October 1, 2013 through December 31, 2013.
	(2)                                 The scheduled maturities of debt are based on the level of borrowings and the available borrowing base as of
	September 30, 2013. Any increases or decreases in the level of borrowings or decreases in the available borrowing base would impact the scheduled maturities of debt during the next five years and thereafter.

Derivative_Financial_Instrumen

Derivative Financial Instruments	9 Months Ended
	Sep. 30, 2013
Derivative Financial Instruments	'
Derivative Financial Instruments	'
	7. Derivative Financial Instruments
	We use financial derivative contracts to manage exposures to commodity price and interest rate fluctuations. We do not hold or issue derivative financial instruments for trading purposes. We manage market and counterparty credit risk in accordance with our policies and guidelines. In accordance with these policies and guidelines, our management determines the appropriate timing and extent of derivative transactions.
	Oil Derivative Contracts
	The following table sets forth the volumes in barrels underlying the Company’s outstanding oil derivative contracts and the weighted average Dated Brent prices per Bbl for those contracts as of September 30, 2013.
						Weighted Average Dated Brent Price per Bbl
	Term(1)	Type of Contract		MBbl		Deferred			Floor			Ceiling			Call
						Premium
						Receivable/
						(Payable)
	2013:00:00
	October - December	Three-way collars		375		$	(4.82	)	$	95		$	105		$	125
	October - December	Three-way collars		253		—			87.5			115			135
	October - December	Three-way collars		250		—			90			115.39			135
	October - December	Three-way collars		250		—			90.08			115			135
	2014:00:00
	January - December	Three-way collars		1,500		(1.22		)	85			115			140
	January - December	Three-way collars		1,000		—			85			115.01			140
	January - December	Three-way collars		1,000		—			88.09			110			125
	January - December	Three-way collars		1,500		1.15			90			113			135
	(1)                                 In October 2013, we entered into put contracts for 1.7 MMBbl from January 2015 through December 2015 with a floor price of $85.00 per Bbl. The put contracts are indexed to Dated Brent prices and have a weighted average deferred premium payable of $3.78 per Bbl.
	Interest Rate Swaps Derivative Contracts
	The following table summarizes our open interest rate swaps as of September 30, 2013, whereby we pay a fixed rate of interest and the counterparty pays a variable LIBOR-based rate:
	Term	Weighted Average			Weighted Average		Floating Rate
		Notional Amount			Fixed Rate
		(In thousands)
	October 2013 — December 2013	$	200,617		1.99	%	6-month LIBOR
	January 2014 — December 2014	133,434			1.99	%	6-month LIBOR
	January 2015 — December 2015	45,319			2.03	%	6-month LIBOR
	January 2016 — June 2016	12,500			2.27	%	6-month LIBOR
	The following tables disclose the Company’s derivative instruments as of September 30, 2013 and December 31, 2012 and gain/(loss) from derivatives during the three and nine months ended September 30, 2013 and 2012, respectively:
				Estimated Fair Value
				Asset (Liability)
				September 30,			December 31,
	Type of Contract	Balance Sheet Location		2013			2012
				(In thousands)
	Derivatives not designated as hedging instruments:
	Derivative assets:
	Commodity(1)	Derivatives assets—current		$	917		$	1,061
	Commodity(2)	Derivatives assets—long-term		1,583			—
	Derivative liabilities:
	Commodity(3)	Derivatives liabilities—current		(6,284		)	(17,005		)
	Interest rate	Derivatives liabilities—current		(3,174		)	(3,372		)
	Commodity(4)	Derivatives liabilities—long-term		(319		)	(659		)
	Interest rate	Derivatives liabilities—long-term		(1,016		)	(2,567		)
	Total derivatives not designated as hedging instruments			$	(8,293	)	$	(22,542	)
	(1)                                 The commodity derivative asset represents $0.9 million of our oil derivative contracts as of September 30, 2013 and $1.1 million of our provisional oil sales contract as of December 31, 2012. Includes deferred premiums receivable of $1.1 million and zero related to commodity derivative contracts as of September 30, 2013 and December 31, 2012, respectively.
	(2)                                 Includes deferred premiums receivable of $0.6 million related to commodity derivative contracts as of September 30, 2013.
	(3)                                 Includes zero and $3.4 million, as of September 30, 2013 and December 31, 2012, respectively of cash settlements made on our commodity derivative contracts which were settled in the month subsequent to period end. Also, includes deferred premiums payable of $3.0 million and $7.6 million related to commodity derivative contracts as of September 30, 2013 and December 31, 2012, respectively.
	(4)                                 Includes deferred premiums payable of $0.6 million and $2.4 million related to commodity derivative contracts as of September 30, 2013 and December 31, 2012, respectively.
				Amount of Gain/(Loss)						Amount of Gain/(Loss)
				Three Months Ended						Nine Months Ended
				September 30,						September 30,
	Type of Contract	Location of Gain/(Loss)		2013			2012			2013			2012
				(In thousands)
	Derivatives in cash flow hedging relationships:
	Interest rate(1)	Interest expense		$	405		$	133		$	1,122		$	(295	)
	Total derivatives in cash flow hedging relationships			$	405		$	133		$	1,122		$	(295	)
	Derivatives not designated as hedging instruments:
	Commodity(2)	Oil and gas revenue		$	(554	)	$	11,494		$	(5,220	)	$	15,221
	Commodity	Derivatives, net		(7,585		)	(24,529		)	(386		)	(26,407		)
	Interest rate	Interest expense		(318		)	(931		)	(268		)	(2,366		)
	Total derivatives not designated as hedging instruments			$	(8,457	)	$	(13,966	)	$	(5,874	)	$	(13,552	)
	(1)                                 Amounts were reclassified from AOCI into earnings upon settlement.
(2)                                 Amounts represent the mark-to-market portion of our provisional oil sales contracts.
In accordance with the mark-to-market method of accounting, the Company recognizes changes in fair values of its derivative contracts as gains or losses in earnings during the period in which they occur. The fair value of the effective portion of the interest rate derivative contracts on May 31, 2010, is reflected in AOCI and is being transferred to interest expense over the remaining term of the contracts. The Company expects to reclassify $1.5 million of gains from AOCI to interest expense within the next 12 months. See Note 8—Fair Value Measurements for additional information regarding the Company’s derivative instruments.
Offsetting of Derivative Assets and Derivative Liabilities
Our derivative instruments subject to master netting arrangements with our counterparties only have the right of offset when there is an event of default.  As of September 30, 2013 and December 31, 2012, there was not an event of default and, therefore, the associated gross asset or gross liability amounts related to these arrangements are presented on the consolidated balance sheets. Additionally, there were no material rights of offset available, if an event of default occurred, as of September 30, 2013 and December 31, 2012.

Fair_Value_Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2013
Fair Value Measurements	'
Fair Value Measurements	'
	8. Fair Value Measurements
	In accordance with ASC 820—Fair Value Measurements and Disclosures, fair value measurements are based upon inputs that market participants use in pricing an asset or liability, which are classified into two categories: observable inputs and unobservable inputs. Observable inputs represent market data obtained from independent sources, whereas unobservable inputs reflect a company’s own market assumptions, which are used if observable inputs are not reasonably available without undue cost and effort. We prioritize the inputs used in measuring fair value into the following fair value hierarchy:
	·                  Level 1—quoted prices for identical assets or liabilities in active markets.
	·                  Level 2—quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability and inputs derived principally from or corroborated by observable market data by correlation or other means.
	·                  Level 3—unobservable inputs for the asset or liability. The fair value input hierarchy level to which an asset or liability measurement in its entirety falls is determined based on the lowest level input that is significant to the measurement in its entirety.
	The following tables present the Company’s assets and liabilities that are measured at fair value on a recurring basis as of September 30, 2013 and December 31, 2012, for each fair value hierarchy level:
		Fair Value Measurements Using:
		Quoted Prices in		Significant Other			Significant
		Active Markets for		Observable Inputs			Unobservable Inputs
		Identical Assets
		(Level 1)		(Level 2)			(Level 3)		Total
		(In thousands)
	September 30, 2013
	Assets:
	Commodity derivatives	$	—	$	2,500		$	—	$	2,500
	Liabilities:
	Commodity derivatives	—		(6,603		)	—		(6,603		)
	Interest rate derivatives	—		(4,190		)	—		(4,190		)
	Total	$	—	$	(8,293	)	$	—	$	(8,293	)
	December 31, 2012
	Assets:
	Commodity derivatives	$	—	$	1,061		$	—	$	1,061
	Liabilities:
	Commodity derivatives	—		(17,664		)	—		(17,664		)
	Interest rate derivatives	—		(5,939		)	—		(5,939		)
	Total	$	—	$	(22,542	)	$	—	$	(22,542	)
	The book values of cash and cash equivalents and restricted cash approximate fair value based on Level 1 inputs. Joint interest billings, oil sales and other receivables, and accounts payable and accrued liabilities approximate fair value due to the short-term nature of these instruments. The carrying values of our debt approximates fair value since they are subject to short-term floating interest rates that approximate the rates available to us for those periods. Our long-term receivables, if any, after any allowances for doubtful accounts approximate fair value. The estimates of fair value of these items are based on Level 2 inputs.
	Commodity Derivatives
	Our commodity derivatives represent crude oil three-way collars for notional barrels of oil at fixed Dated Brent oil prices. The values attributable to the our oil derivatives are based on (i) the contracted notional volumes, (ii) independent active futures price quotes for Dated Brent, (iii) a credit-adjusted yield curve applicable to each counterparty by reference to the CDS market and (iv) an independently sourced estimate of volatility for Dated Brent. The volatility estimate was provided by certain independent brokers who are active in buying and selling oil options and was corroborated by market-quoted volatility factors. The deferred premium is included in the fair market value of the puts and compound options. See Note 7—Derivative Financial Instruments for additional information regarding the Company’s derivative instruments.
	Provisional Oil Sales
	The value attributable to the provisional oil sales derivative is based on (i) the sales volumes subject to provisional pricing and (ii) an independently sourced forward curve over the term of the provisional pricing period.
	Interest Rate Derivatives
	We have interest rate swaps, whereby the Company pays a fixed rate of interest and the counterparty pays a variable LIBOR-based rate. The values attributable to the Company’s interest rate derivative contracts are based on (i) the contracted notional amounts, (ii) LIBOR yield curves provided by independent third parties and corroborated with forward active market-quoted LIBOR yield curves and (iii) a credit-adjusted yield curve as applicable to each counterparty by reference to the CDS market.

Equitybased_Compensation

Equity-based Compensation	9 Months Ended
	Sep. 30, 2013
Equity-based Compensation	'
Equity-based Compensation	'
	9. Equity-based Compensation
	Restricted Stock Awards and Restricted Stock Units
	We record compensation expense equal to the fair value of share-based payments over the vesting periods of the Long-Term Incentive Plan (“LTIP”) awards. We recorded compensation expense from awards granted under our LTIP of $13.8 million and $19.4 million during the three months ended September 30, 2013 and 2012, respectively, and $50.8 million and $58.2 million during the nine months ended September 30, 2013 and 2012, respectively. The tax benefit resulting from equity-based compensation expense for the three months ended September 30, 2013 and 2012 was $4.8 million and $6.7 million, respectively, and for the nine months ended September 30, 2013 and 2012 was $17.4 million and $20.2 million, respectively. Additionally, we expensed a tax shortfall (the difference between the estimated tax deduction on the grant date and the actual tax deduction on the vest date) of $6.9 million and $7.4 million during the nine months ended September 30, 2013 and 2012, respectively. No shortfall occurred during the three months ended September 30, 2013 and 2012.
	The following table reflects the outstanding restricted stock awards as of September 30, 2013:
				Weighted-		Market / Service		Weighted-
		Service Vesting		Average		Vesting		Average
		Restricted Stock		Grant-Date		Restricted Stock		Grant-Date
		Awards		Fair Value		Awards		Fair Value
		(In thousands)				(In thousands)
	Outstanding at December 31, 2012	9,898		$	16.92	3,534		$	12.93
	Granted	351		10.73		—		—
	Forfeited	(462	)	16.51		(93	)	12.45
	Vested	(3,358	)	17.26		—		—
	Outstanding at September 30, 2013	6,429		16.44		3,441		12.94
	The following table reflects the outstanding restricted stock units as of September 30, 2013:
				Weighted-		Market / Service		Weighted-
		Service Vesting		Average		Vesting		Average
		Restricted Stock		Grant-Date		Restricted Stock		Grant-Date
		Units		Fair Value		Units		Fair Value
		(In thousands)				(In thousands)
	Outstanding at December 31, 2012	1,023		$	10.59	825		$	15.81
	Granted	1,512		10.8		1,074		15.44
	Forfeited	(133	)	10.53		(73	)	15.74
	Vested	(225	)	10.51		—		—
	Outstanding at September 30, 2013	2,177		10.75		1,826		15.6
	As of September 30, 2013, total equity-based compensation to be recognized on unvested restricted stock awards and restricted stock units is $144.7 million over a weighted average period of 2.20 years. At September 30, 2013, the Company had approximately 5.5 million shares that remain available for issuance under the LTIP.
	For restricted stock awards with a combination of market and service vesting criteria, the number of common shares to be issued is determined by comparing the Company’s total shareholder return with the total shareholder return of a predetermined group of peer companies over the performance period and can vest in up to 100% of the awards granted. The grant date fair value of these awards ranged from $6.70 to $13.57 per award. The Monte Carlo simulation model used to estimate the grant-date fair value utilizes multiple input variables that determine the probability of satisfying the market condition stipulated in the award grant and calculates the fair value of the award. The expected volatility utilized in the model was estimated using our historical volatility and the historical volatilities of our peer companies and ranged from 41.3% to 56.7%. The risk-free interest rate was based on the U.S. treasury rate for a term commensurate with the expected life of the grant and ranged from 0.5% to 1.1%.
	For restricted stock units with a combination of market and service vesting criteria, the number of common shares to be issued is determined by comparing the Company’s total shareholder return with the total shareholder return of a predetermined group of peer companies over the performance period and can vest in up to 200% of the awards granted. The grant date fair value of these awards ranged from $15.44 to $15.81 per award. The Monte Carlo simulation model used to estimate the grant-date fair value utilizes multiple input variables that determine the probability of satisfying the market condition stipulated in the award grant and calculates the fair value of the award. The expected volatility utilized in the model was estimated using our historical volatility and the historical volatilities of our peer companies and ranged from 53.0% to 54.0%. The risk-free interest rate was based on the U.S. treasury rate for a term commensurate with the expected life of the grant and ranged from 0.5% to 0.7%.

Income_Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2013
Income Taxes	'
Income Taxes	'
	10. Income Taxes
	Income tax expense was $34.2 million and $25.9 million for the three months ended September 30, 2013 and 2012, respectively, and was $124.6 million and $64.7 million for the nine months ended September 30, 2013 and 2012, respectively. The income tax provision consists of U.S. and Ghanaian income and Texas margin taxes.
	The components of income (loss) before income taxes were as follows:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2013			2012			2013			2012
		(In thousands)
	Bermuda	$	(5,880	)	$	(2,316	)	$	(19,320	)	$	(8,735	)
	United States	2,740			3,145			8,014			9,492
	Foreign—other	(7,124		)	(11,156		)	40,664			(34,661		)
	Income (loss) before income taxes	$	(10,264	)	$	(10,327	)	$	29,358		$	(33,904	)
	Our effective tax rate for the three months ended September 30, 2013 and 2012 is (333)% and (251)%, respectively. For the nine months ended, September 30, 2013 and 2012, our effective tax rate is 424% and (191)%. The effective tax rate for the United States is approximately 42% and 43% for the three months ended September 30, 2013 and 2012, respectively, and 125% and 116% for the nine months ended September 30, 2013 and 2012, respectively. The high effective tax rates in the United States are due to the effect of tax shortfalls related to equity-based compensation. The effective tax rate for Ghana is approximately 36% and 39% for the three months ended September 30, 2013 and 2012, respectively, and 36% and 37% for the nine months ended September 30, 2013 and 2012, respectively. Our other foreign jurisdictions have a 0% effective tax rate because they reside in countries with a 0% statutory rate, or we have experienced losses in those countries and have a full valuation allowance reserved against the corresponding net deferred tax assets.
	The Company has no material unrecognized income tax benefits.
	A subsidiary of the Company files a U.S. federal income tax return and a Texas margin tax return. In addition to the United States, the Company files income tax returns in the countries in which the Company operates. The Company is open to U.S. federal income tax examinations for tax years 2009 through 2012 and to Texas margin tax examinations for the tax years 2008 through 2012. In addition, the Company is open to income tax examinations for years 2004 through 2012 in Ghana.
	As of September 30, 2013, the Company had no material uncertain tax positions. The Company’s policy is to recognize potential interest and penalties related to income tax matters in income tax expense, but has not accrued any material amounts to date.

Net_Income_Loss_Per_Share

Net Income (Loss) Per Share	9 Months Ended
	Sep. 30, 2013
Net Income (Loss) Per Share	'
Net Income (Loss) Per Share	'
	11. Net Income (Loss) Per Share
	The following table is a reconciliation between net income (loss) and the amounts used to compute basic and diluted net income (loss) per share and the weighted average shares outstanding used to compute basic and diluted net income (loss) per share:
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2013			2012			2013			2012
		(In thousands, except per share data)
	Numerator:
	Net income (loss)	$	(44,488	)	$	(36,250	)	$	(95,210	)	$	(98,634	)
	Less: Basic income allocable to participating securities(1)	—			—			—			—
	Basic net income (loss) allocable to common shareholders	(44,488		)	(36,250		)	(95,210		)	(98,634		)
	Diluted adjustments to income allocable to participating securities(1)	—			—			—			—
	Diluted net income (loss) allocable to common shareholders	$	(44,488	)	$	(36,250	)	$	(95,210	)	$	(98,634	)
	Denominator:
	Weighted average number of shares used to compute net income (loss) per share:
	Basic	377,654			373,448			376,509			371,140
	Restricted stock awards and units(1)(2)	—			—			—			—
	Diluted	377,654			373,448			376,509			371,140
	Net income (loss) per share:
	Basic	$	(0.12	)	$	(0.10	)	$	(0.25	)	$	(0.27	)
	Diluted	$	(0.12	)	$	(0.10	)	$	(0.25	)	$	(0.27	)
	(1)                                 Our service vesting restricted stock awards represent participating securities because they participate in nonforfeitable dividends with common equity owners. Income allocable to participating securities represents the distributed and undistributed earnings attributable to the participating securities. Our restricted stock awards with market and service vesting criteria and all restricted stock units are not considered to be participating securities and, therefore, are excluded from the basic net income (loss) per common share calculation. Our service vesting restricted stock awards do not participate in undistributed net losses and, therefore, are excluded from the basic net income (loss) per common share calculation in periods we are in a net loss position.
	(2)                                 We excluded outstanding restricted stock awards and units of 13.9 million and 17.1 million for the three months ended September 30, 2013 and 2012, respectively, and 13.9 million and 17.1 million for the nine months ended September 30, 2013 and 2012, respectively, from the computations of diluted net income per share because the effect would have been anti-dilutive.

Commitments_and_Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2013
Commitments and Contingencies	'
Commitments and Contingencies	'
	12. Commitments and Contingencies
	We are involved in litigation, regulatory examinations and administrative proceedings primarily arising in the ordinary course of our business in jurisdictions in which we do business. Although the outcome of these matters cannot be predicted with certainty, management believes none of these matters, either individually or in the aggregate, would have a material effect upon the Company’s consolidated financial statements; however, an unfavorable outcome could have a material adverse effect on our results from operations for a specific interim period or year.
	In June 2013, we signed a long-term rig agreement with a subsidiary of Atwood Oceanics, Inc. for the new build drillship “Atwood Achiever.” Currently under construction, the rig is scheduled for completion in June 2014 and expected to commence drilling operations in the second half of 2014. The rig agreement covers an initial period of three years at a day rate of approximately $0.6 million, with an option to extend the agreement for an additional three-year term.
	The estimated future minimum commitments under this contract as of September 30, 2013, are:
		Payments Due By Year(1)
		Total		2013(2)		2014		2015		2016		2017		Thereafter
		(In thousands)
	Atwood Achiever drilling rig contract (3)	$	651,525	$	—	$	90,440	$	217,175	$	217,770	$	126,140	$	—
	(1)                                 Does not include purchase commitments for jointly owned fields and facilities where we are not the operator, excludes commitments for development activities under our petroleum contracts where we are not the operator and excludes commitments for exploration activities, including well commitments, in our petroleum contracts and farm-in agreements.
	(2)                                 Represents payments for the period from October 1, 2013 through December 31, 2013.
	(3)                                 Commitments calculated using a day rate of $595,000 and an estimated rig delivery date of August 1, 2014.

Subsequent_Events

Subsequent Events	9 Months Ended
	Sep. 30, 2013
Subsequent Events	'
Subsequent Events	'
	13. Subsequent Events
	In October 2013, we entered into three farm-out agreements with BP plc (“BP”) covering three blocks in the Agadir Basin, offshore Morocco. Under the terms of the agreements, BP will acquire a non-operating interest in each of the Essaouira Offshore, Foum Assaka Offshore and Tarhazoute Offshore blocks. BP will fund Kosmos’ share of the cost of one exploration well in each of the three blocks, subject to a maximum spend of $120.0 million per well, and pay its proportionate share of any well costs above the maximum spend. In the event a second exploration well is drilled in any block, BP will pay 150% of its share of costs subject to a maximum spend of $120.0 million per well. BP shall also pay $36.3 million for their share of past costs. Completion of the transactions is subject to customary closing conditions, including Moroccan Government approvals. After completing the transaction, our participating interests will be 30.0%, 29.925% and 30.0% in the Essaouira, Foum Assaka and Tarhazoute Offshore blocks, respectively, and we will remain the operator.
	In October 2013, we entered into a farm-out agreement with Capricorn Exploration & Development Company Limited, a wholly owned subsidiary of Cairn Energy PLC (“Cairn”), covering the Cap Boujdour Contract Area, offshore Western Sahara. Under the terms of the agreement, Cairn will acquire a 20% non-operated interest in the exploration permits comprising the Cap Boujdour Contract Area. Cairn will pay 150% of its share of costs of a 3D seismic survey and one exploration well capped at $125.0 million. In the event the exploration well is successful, Cairn will pay 200% of its share of costs on two appraisal wells capped at $100.0 million per well. Additionally, Cairn will contribute $12.3 million towards our future costs. Completion of the transaction is subject to customary closing conditions, including Moroccan Government approvals. After completing the transaction, our participating interest in the Cap Boujdour Contract Area will be 55.0% and we will remain the operator.
	Drilling of the Akasa-2A appraisal well on the WCTP Block was completed in October 2013. The Akasa-2A appraisal well did not encounter oil or gas reserves sufficient to be utilized as a producing well. Accounting rules require that the costs associated with the Akasa-2A appraisal well be impaired, which are $11.5 million and included in exploration expenses in the accompanying consolidated statement of operations. We estimate we will incur an additional $8.9 million of related well costs, which will be expensed as incurred.

Accounting_Policies_Policies

Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2013
Accounting Policies	'
General	'
	General
	The interim-period financial information presented in the consolidated financial statements included in this report is unaudited and, in the opinion of management, includes all adjustments of a normal recurring nature necessary to present fairly the consolidated financial position as of September 30, 2013, the changes in the consolidated statements of shareholders’ equity for the nine months ended September 30, 2013, the consolidated results of operations for the three and nine months ended September 30, 2013 and 2012, and consolidated cash flows for the nine months ended September 30, 2013 and 2012. The results of the interim periods shown in this report are not necessarily indicative of the final results to be expected for the full year. The consolidated financial statements were prepared in accordance with the requirements of the Securities and Exchange Commission (“SEC”) for interim reporting. As permitted under those rules, certain notes or other financial information that are normally required by Generally Accepted Accounting Principles (“GAAP”) have been condensed or omitted from these interim consolidated financial statements. These consolidated financial statements and the accompanying notes should be read in conjunction with our audited consolidated financial statements for the year ended December 31, 2012, included in our annual report on Form 10-K.
Reclassifications	'
	Reclassifications
	Certain prior period amounts have been reclassified to conform with the current year presentation. Such reclassifications had no impact on our reported net loss, current assets, total assets, current liabilities, total liabilities or shareholders’ equity.
Restricted Cash	'
	Restricted Cash
	In accordance with our commercial debt facility, we are required to maintain a restricted cash balance that is sufficient to meet the payment of interest and fees for the next six-month period. As of September 30, 2013 and December 31, 2012, we had $19.4 million and $21.3 million, respectively, in current restricted cash to meet this requirement. In addition, in accordance with certain of our petroleum contracts, we have posted letters of credit related to performance guarantees for our minimum work obligations. These letters of credit are cash collateralized in accounts held by us and as such are classified as restricted cash. Upon completion of the minimum work obligations and/or entering into the next phase of the petroleum contract, the requirement to post letters of credit will be satisfied and the cash collateral will be released. As of September 30, 2013 and December 31, 2012, we had $24.6 million and $29.9 million, respectively, of long-term restricted cash used to cash collateralize performance guarantees related to our petroleum contracts.
Inventories	'
	Inventories
	Inventories consisted of $32.3 million and $33.1 million of materials and supplies and $0.8 million and $0.2 million of hydrocarbons as of September 30, 2013 and December 31, 2012, respectively. The Company’s materials and supplies inventory primarily consists of casing and wellheads and is stated at the lower of cost, using the weighted average cost method, or market.
	Hydrocarbon inventory is carried at the lower of cost, using the weighted average cost method, or market. Hydrocarbon inventory costs include expenditures and other charges directly and indirectly incurred in bringing the inventory to its existing condition. Selling expenses and general and administrative expenses are reported as period costs and excluded from inventory costs.
Variable Interest Entity	'
	Variable Interest Entity
	Our wholly owned subsidiary, Kosmos Energy Finance International, is a variable interest entity (“VIE”). The Company is the primary beneficiary of this VIE, which is consolidated in these financial statements.
	Kosmos Energy Finance International’s following assets and liabilities are shown separately on the face of the consolidated balance sheet as of September 30, 2013 and December 31, 2012: current restricted cash; long-term derivatives assets; long-term debt; and current and long-term derivatives liabilities. At September 30, 2013, Kosmos Energy Finance International had $36.9 million in cash and cash equivalents; $0.4 million in prepaid expenses and other; $0.9 million current derivative assets; $36.2 million deferred financing costs, net; $1.5 million in accrued liabilities and $7.6 million in other long-term liabilities, which are included in the amounts shown on the face of the consolidated balance sheet. At December 31, 2012, Kosmos Energy Finance International had $118.8 million in cash and cash equivalents; $0.2 million in prepaid expenses and other; $42.2 million deferred financing costs, net; $0.5 million in accrued liabilities and $6.6 million in other long-term liabilities, which are included in the amounts shown on the face of the consolidated balance sheet.

Property_and_Equipment_Tables

Property and Equipment (Tables)	9 Months Ended
	Sep. 30, 2013
Property and Equipment	'
Schedule of property and equipment	'
		September 30,			December 31,
		2013			2012
		(In thousands)
	Oil and gas properties:
	Proved properties	$	767,288		$	682,276
	Unproved properties	489,874			454,391
	Support equipment and facilities	712,415			687,835
	Total oil and gas properties	1,969,577			1,824,502
	Less: accumulated depletion	(483,353		)	(314,190		)
	Oil and gas properties, net	1,486,224			1,510,312
	Other property	30,978			27,316
	Less: accumulated depreciation	(15,488		)	(11,866		)
	Other property, net	15,490			15,450
	Property and equipment, net	$	1,501,714		$	1,525,762

Suspended_Well_Costs_Tables

Suspended Well Costs (Tables)	9 Months Ended
	Sep. 30, 2013
Suspended Well Costs	'
Schedule of capitalized exploratory well costs	'
		Nine Months
		Ended
		September 30,
		2013
		(In thousands)
	Beginning balance	$	372,492
	Additions to capitalized exploratory well costs pending the determination of proved reserves	30,415
	Reclassification due to determination of proved reserves	—
	Capitalized exploratory well costs charged to expense	(26,997		)
	Ending balance	$	375,910
Schedule of aging of capitalized exploratory well costs and number of projects for which exploratory well costs were capitalized for more than one year	'
		September 30, 2013			December 31, 2012
		(In thousands, except well counts)
	Exploratory well costs capitalized for a period of one year or less	$	11,470		$	106,635
	Exploratory well costs capitalized for a period one to two years	228,842			179,933
	Exploratory well costs capitalized for a period three to four years	135,598			85,924
	Ending balance	$	375,910		$	372,492
	Number of projects that have exploratory well costs that have been capitalized for a period greater than one year	8			7

Accounts_Payable_and_Accrued_L1

Accounts Payable and Accrued Liabilities (Tables)	9 Months Ended
	Sep. 30, 2013
Accounts Payable and Accrued Liabilities	'
Schedule of components of accrued liabilities	'
		September 30,		December 31,
		2013		2012
		(In thousands)
	Accrued liabilities:
	Accrued exploration, development and production	$	65,561	$	20,616
	Accrued general and administrative expenses	14,896		5,089
	Accrued taxes other than income	15,667		11,124
	Accrued derivative settlements	1,465		—
	Income taxes	18,277		4,192
		$	115,866	$	41,021

Debt_Tables

Debt (Tables)	9 Months Ended
	Sep. 30, 2013
Debt	'
Schedule of estimated repayments of debt	'
		Payments Due by Year
		2013(1)		2014		2015		2016		2017		Thereafter
		(In thousands)
	Facility(2)	$	—	$	—	$	346,693	$	149,428	$	292,768	$	111,111
	(1)                                 Represents payments for the period October 1, 2013 through December 31, 2013.
	(2)                                 The scheduled maturities of debt are based on the level of borrowings and the available borrowing base as of
	September 30, 2013. Any increases or decreases in the level of borrowings or decreases in the available borrowing base would impact the scheduled maturities of debt during the next five years and thereafter.

Derivative_Financial_Instrumen1

Derivative Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2013
Derivative Financial Instruments	'
Schedule of oil derivative contracts	'
						Weighted Average Dated Brent Price per Bbl
	Term(1)	Type of Contract		MBbl		Deferred			Floor			Ceiling			Call
						Premium
						Receivable/
						(Payable)
	2013:00:00
	October - December	Three-way collars		375		$	(4.82	)	$	95		$	105		$	125
	October - December	Three-way collars		253		—			87.5			115			135
	October - December	Three-way collars		250		—			90			115.39			135
	October - December	Three-way collars		250		—			90.08			115			135
	2014:00:00
	January - December	Three-way collars		1,500		(1.22		)	85			115			140
	January - December	Three-way collars		1,000		—			85			115.01			140
	January - December	Three-way collars		1,000		—			88.09			110			125
	January - December	Three-way collars		1,500		1.15			90			113			135
	(1)                                 In October 2013, we entered into put contracts for 1.7 MMBbl from January 2015 through December 2015 with a floor price of $85.00 per Bbl. The put contracts are indexed to Dated Brent prices and have a weighted average deferred premium payable of $3.78 per Bbl.
Schedule of interest rate swaps derivative contracts	'
	Term	Weighted Average			Weighted Average		Floating Rate
		Notional Amount			Fixed Rate
		(In thousands)
	October 2013 — December 2013	$	200,617		1.99	%	6-month LIBOR
	January 2014 — December 2014	133,434			1.99	%	6-month LIBOR
	January 2015 — December 2015	45,319			2.03	%	6-month LIBOR
	January 2016 — June 2016	12,500			2.27	%	6-month LIBOR
Schedule of derivative instruments by balance sheet location	'
				Estimated Fair Value
				Asset (Liability)
				September 30,			December 31,
	Type of Contract	Balance Sheet Location		2013			2012
				(In thousands)
	Derivatives not designated as hedging instruments:
	Derivative assets:
	Commodity(1)	Derivatives assets—current		$	917		$	1,061
	Commodity(2)	Derivatives assets—long-term		1,583			—
	Derivative liabilities:
	Commodity(3)	Derivatives liabilities—current		(6,284		)	(17,005		)
	Interest rate	Derivatives liabilities—current		(3,174		)	(3,372		)
	Commodity(4)	Derivatives liabilities—long-term		(319		)	(659		)
	Interest rate	Derivatives liabilities—long-term		(1,016		)	(2,567		)
	Total derivatives not designated as hedging instruments			$	(8,293	)	$	(22,542	)
	(1)                                 The commodity derivative asset represents $0.9 million of our oil derivative contracts as of September 30, 2013 and $1.1 million of our provisional oil sales contract as of December 31, 2012. Includes deferred premiums receivable of $1.1 million and zero related to commodity derivative contracts as of September 30, 2013 and December 31, 2012, respectively.
	(2)                                 Includes deferred premiums receivable of $0.6 million related to commodity derivative contracts as of September 30, 2013.
	(3)                                 Includes zero and $3.4 million, as of September 30, 2013 and December 31, 2012, respectively of cash settlements made on our commodity derivative contracts which were settled in the month subsequent to period end. Also, includes deferred premiums payable of $3.0 million and $7.6 million related to commodity derivative contracts as of September 30, 2013 and December 31, 2012, respectively.
	(4)                                 Includes deferred premiums payable of $0.6 million and $2.4 million related to commodity derivative contracts as of September 30, 2013 and December 31, 2012, respectively.
Schedule of derivative instruments by location of gain/(loss)	'
				Amount of Gain/(Loss)						Amount of Gain/(Loss)
				Three Months Ended						Nine Months Ended
				September 30,						September 30,
	Type of Contract	Location of Gain/(Loss)		2013			2012			2013			2012
				(In thousands)
	Derivatives in cash flow hedging relationships:
	Interest rate(1)	Interest expense		$	405		$	133		$	1,122		$	(295	)
	Total derivatives in cash flow hedging relationships			$	405		$	133		$	1,122		$	(295	)
	Derivatives not designated as hedging instruments:
	Commodity(2)	Oil and gas revenue		$	(554	)	$	11,494		$	(5,220	)	$	15,221
	Commodity	Derivatives, net		(7,585		)	(24,529		)	(386		)	(26,407		)
	Interest rate	Interest expense		(318		)	(931		)	(268		)	(2,366		)
	Total derivatives not designated as hedging instruments			$	(8,457	)	$	(13,966	)	$	(5,874	)	$	(13,552	)
	(1)                                 Amounts were reclassified from AOCI into earnings upon settlement.
	(2)                                 Amounts represent the mark-to-market portion of our provisional oil sales contracts.

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2013
Fair Value Measurements	'
Schedule of Company's assets and liabilities that are measured at fair value on a recurring basis	'
		Fair Value Measurements Using:
		Quoted Prices in		Significant Other			Significant
		Active Markets for		Observable Inputs			Unobservable Inputs
		Identical Assets
		(Level 1)		(Level 2)			(Level 3)		Total
		(In thousands)
	September 30, 2013
	Assets:
	Commodity derivatives	$	—	$	2,500		$	—	$	2,500
	Liabilities:
	Commodity derivatives	—		(6,603		)	—		(6,603		)
	Interest rate derivatives	—		(4,190		)	—		(4,190		)
	Total	$	—	$	(8,293	)	$	—	$	(8,293	)
	December 31, 2012
	Assets:
	Commodity derivatives	$	—	$	1,061		$	—	$	1,061
	Liabilities:
	Commodity derivatives	—		(17,664		)	—		(17,664		)
	Interest rate derivatives	—		(5,939		)	—		(5,939		)
	Total	$	—	$	(22,542	)	$	—	$	(22,542	)

Equitybased_Compensation_Table

Equity-based Compensation (Tables) (LTIP)	9 Months Ended
	Sep. 30, 2013
Restricted stock awards	'
Equity-based Compensation	'
Schedule of plan activity	'
				Weighted-		Market / Service		Weighted-
		Service Vesting		Average		Vesting		Average
		Restricted Stock		Grant-Date		Restricted Stock		Grant-Date
		Awards		Fair Value		Awards		Fair Value
		(In thousands)				(In thousands)
	Outstanding at December 31, 2012	9,898		$	16.92	3,534		$	12.93
	Granted	351		10.73		—		—
	Forfeited	(462	)	16.51		(93	)	12.45
	Vested	(3,358	)	17.26		—		—
	Outstanding at September 30, 2013	6,429		16.44		3,441		12.94
Restricted stock units	'
Equity-based Compensation	'
Schedule of plan activity	'
				Weighted-		Market / Service		Weighted-
		Service Vesting		Average		Vesting		Average
		Restricted Stock		Grant-Date		Restricted Stock		Grant-Date
		Units		Fair Value		Units		Fair Value
		(In thousands)				(In thousands)
	Outstanding at December 31, 2012	1,023		$	10.59	825		$	15.81
	Granted	1,512		10.8		1,074		15.44
	Forfeited	(133	)	10.53		(73	)	15.74
	Vested	(225	)	10.51		—		—
	Outstanding at September 30, 2013	2,177		10.75		1,826		15.6

Income_Taxes_Tables

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2013
Income Taxes	'
Schedule of components of income (loss) before income taxes	'
		Three Months Ended September 30,						Nine Months Ended September 30,
		2013			2012			2013			2012
		(In thousands)
	Bermuda	$	(5,880	)	$	(2,316	)	$	(19,320	)	$	(8,735	)
	United States	2,740			3,145			8,014			9,492
	Foreign—other	(7,124		)	(11,156		)	40,664			(34,661		)
	Income (loss) before income taxes	$	(10,264	)	$	(10,327	)	$	29,358		$	(33,904	)

Net_Income_Loss_Per_Share_Tabl

Net Income (Loss) Per Share (Tables)	9 Months Ended
	Sep. 30, 2013
Net Income (Loss) Per Share	'
Schedule of reconciliation between net income (loss) and the amounts used to compute basic and diluted net income (loss) per share and the weighted average shares outstanding used to compute basic and diluted net income (loss) per share	'
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2013			2012			2013			2012
		(In thousands, except per share data)
	Numerator:
	Net income (loss)	$	(44,488	)	$	(36,250	)	$	(95,210	)	$	(98,634	)
	Less: Basic income allocable to participating securities(1)	—			—			—			—
	Basic net income (loss) allocable to common shareholders	(44,488		)	(36,250		)	(95,210		)	(98,634		)
	Diluted adjustments to income allocable to participating securities(1)	—			—			—			—
	Diluted net income (loss) allocable to common shareholders	$	(44,488	)	$	(36,250	)	$	(95,210	)	$	(98,634	)
	Denominator:
	Weighted average number of shares used to compute net income (loss) per share:
	Basic	377,654			373,448			376,509			371,140
	Restricted stock awards and units(1)(2)	—			—			—			—
	Diluted	377,654			373,448			376,509			371,140
	Net income (loss) per share:
	Basic	$	(0.12	)	$	(0.10	)	$	(0.25	)	$	(0.27	)
	Diluted	$	(0.12	)	$	(0.10	)	$	(0.25	)	$	(0.27	)
	(1)                                 Our service vesting restricted stock awards represent participating securities because they participate in nonforfeitable dividends with common equity owners. Income allocable to participating securities represents the distributed and undistributed earnings attributable to the participating securities. Our restricted stock awards with market and service vesting criteria and all restricted stock units are not considered to be participating securities and, therefore, are excluded from the basic net income (loss) per common share calculation. Our service vesting restricted stock awards do not participate in undistributed net losses and, therefore, are excluded from the basic net income (loss) per common share calculation in periods we are in a net loss position.
	(2)                                 We excluded outstanding restricted stock awards and units of 13.9 million and 17.1 million for the three months ended September 30, 2013 and 2012, respectively, and 13.9 million and 17.1 million for the nine months ended September 30, 2013 and 2012, respectively, from the computations of diluted net income per share because the effect would have been anti-dilutive.

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2013
Commitments and Contingencies	'
Schedule of estimated future minimum commitments	'
		Payments Due By Year(1)
		Total		2013(2)		2014		2015		2016		2017		Thereafter
		(In thousands)
	Atwood Achiever drilling rig contract (3)	$	651,525	$	—	$	90,440	$	217,175	$	217,770	$	126,140	$	—
	(1)                                 Does not include purchase commitments for jointly owned fields and facilities where we are not the operator, excludes commitments for development activities under our petroleum contracts where we are not the operator and excludes commitments for exploration activities, including well commitments, in our petroleum contracts and farm-in agreements.
	(2)                                 Represents payments for the period from October 1, 2013 through December 31, 2013.
	(3)                                 Commitments calculated using a day rate of $595,000 and an estimated rig delivery date of August 1, 2014.

Organization_Details

Organization (Details)	9 Months Ended
	Sep. 30, 2013
	segment
Organization	'
Number of reportable segments	1

Accounting_Policies_Details

Accounting Policies (Details) (USD $)	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Restricted Cash	'	'
Current restricted cash	$19,377,000	$21,341,000
Long-term restricted cash	24,634,000	29,884,000
Inventories	'	'
Materials and supplies inventory	32,300,000	33,100,000
Hydrocarbons inventory	800,000	200,000
Restricted Cash | Commercial Debt Facility	'	'
Restricted Cash	'	'
Restricted cash period required as per commercial debt facility to meet interest and commitment fee payments	'6 months	'
Current restricted cash	19,400,000	21,300,000
Restricted Cash | Petroleum agreements - performance guarantees	'	'
Restricted Cash	'	'
Long-term restricted cash	$24,600,000	$29,900,000

Accounting_Policies_Details_2

Accounting Policies (Details 2) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Variable interest entity	'	'	'	'
Cash and cash equivalents	$440,267	$515,164	$399,650	$673,092
Prepaid expenses and other	11,596	10,470	'	'
Current derivative assets	917	1,061	'	'
Deferred financing costs, net	42,897	50,214	'	'
Accrued liabilities	115,866	41,021	'	'
Other long-term liabilities	18,886	12,117	'	'
Kosmos Energy Finance International	'	'	'	'
Variable interest entity	'	'	'	'
Cash and cash equivalents	36,900	118,800	'	'
Prepaid expenses and other	400	200	'	'
Current derivative assets	900	'	'	'
Deferred financing costs, net	36,200	42,200	'	'
Accrued liabilities	1,500	500	'	'
Other long-term liabilities	$7,600	$6,600	'	'

Property_and_Equipment_Details

Property and Equipment (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Oil and gas properties:	'	'	'	'	'
Proved properties	$767,288,000	'	$767,288,000	'	$682,276,000
Unproved properties	489,874,000	'	489,874,000	'	454,391,000
Support equipment and facilities	712,415,000	'	712,415,000	'	687,835,000
Total oil and gas properties	1,969,577,000	'	1,969,577,000	'	1,824,502,000
Less: accumulated depletion	-483,353,000	'	-483,353,000	'	-314,190,000
Oil and gas properties, net	1,486,224,000	'	1,486,224,000	'	1,510,312,000
Other property	30,978,000	'	30,978,000	'	27,316,000
Less: accumulated depreciation	-15,488,000	'	-15,488,000	'	-11,866,000
Other property, net	15,490,000	'	15,490,000	'	15,450,000
Property and equipment, net	1,501,714,000	'	1,501,714,000	'	1,525,762,000
Depletion expense	$56,100,000	$61,900,000	$169,200,000	$123,300,000	'

Suspended_Well_Costs_Details

Suspended Well Costs (Details) (USD $)	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
	project	project
Suspended Well Costs	'	'
Capitalized exploratory well costs subsequently expensed in the same period	$69,800,000	'
Reconciliation of capitalized exploratory well costs on completed wells	'	'
Balance at the beginning of the period	372,492,000	'
Additions to capitalized exploratory well costs pending the determination of proved reserves	30,415,000	'
Capitalized exploratory well costs charged to expense	-26,997,000	'
Balance at the end of the period	375,910,000	'
Aging of capitalized exploratory well costs and number of projects for which exploratory well costs were capitalized for more than one year	'	'
Exploratory well costs capitalized for a period of one year or less	11,470,000	106,635,000
Exploratory well costs capitalized for a period one to two years	228,842,000	179,933,000
Exploratory well costs capitalized for a period three to four years	135,598,000	85,924,000
Ending balance	$375,910,000	'
Number of projects that have exploratory well costs that have been capitalized for a period greater than one year	8	7
Mahogany East Area | Minimum	'	'
Projects with exploratory well costs capitalized for more than one year	'	'
Period of negotiation and consultation of notice of dispute issued to Ministry of Energy by the entity	'30 days	'
Teak-1 Discovery	'	'
Projects with exploratory well costs capitalized for more than one year	'	'
Number of appraisal wells which were drilled	2	'
Teak-1 Discovery | Maximum	'	'
Projects with exploratory well costs capitalized for more than one year	'	'
Submission of PoD to Ghana's Ministry of Energy, period	'6 months	'
Teak-2 Discovery | Maximum	'	'
Projects with exploratory well costs capitalized for more than one year	'	'
Submission of PoD to Ghana's Ministry of Energy, period	'6 months	'
Akasa Discovery | Maximum	'	'
Projects with exploratory well costs capitalized for more than one year	'	'
Submission of PoD to Ghana's Ministry of Energy, period	'6 months	'
TEN Discoveries | Forecast	'	'
Projects with exploratory well costs capitalized for more than one year	'	'
Portion of wells designed as producers (as a percent)	50.00%	'
Portion of wells for water and gas injection (as a percent)	50.00%	'
TEN Discoveries | Maximum | Forecast	'	'
Projects with exploratory well costs capitalized for more than one year	'	'
Number of wells developed	24	'
Wawa Discovery | Maximum	'	'
Projects with exploratory well costs capitalized for more than one year	'	'
Submission of PoD to Ghana's Ministry of Energy, period	'6 months	'

Accounts_Payable_and_Accrued_L2

Accounts Payable and Accrued Liabilities (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Accounts Payable and Accrued Liabilities	'	'
Accounts payable	$98,818	$128,855
Accrued liabilities:	'	'
Accrued exploration, development and production	65,561	20,616
Accrued general and administrative expenses	14,896	5,089
Accrued taxes other than income	15,667	11,124
Accrued derivative settlements	1,465	'
Income taxes	18,277	4,192
Accrued liabilities	$115,866	$41,021

Debt_Details

Debt (Details) (USD $)	Sep. 30, 2013	Nov. 30, 2012	Mar. 31, 2011	Sep. 30, 2013	Apr. 30, 2013	Dec. 31, 2012	Jul. 31, 2013	Sep. 30, 2013	Jul. 31, 2013
	Facility	Facility	Facility	Corporate Revolver	Corporate Revolver	Corporate Revolver	Revolving Letter of Credit Facility	Revolving Letter of Credit Facility	Revolving Letter of Credit Facility
								item	Minimum
Debt	'	'	'	'	'	'	'	'	'
Available amount under facility	'	$1,500,000,000	$2,000,000,000	'	$300,000,000	$260,000,000	$100,000,000	'	'
Reduction in undrawn availability	89,600,000	'	'	'	'	'	'	'	'
Current borrowing capacity	1,200,000,000	'	'	'	'	'	'	'	'
Amount outstanding	900,000,000	'	'	0	'	'	'	29,000,000	'
Undrawn availability	309,500,000	'	'	300,000,000	'	'	'	'	'
Letters of credit drawn	0	'	'	'	'	'	'	'	'
Scheduled maturities of debt during the five year period and thereafter	'	'	'	'	'	'	'	'	'
2015	346,693,000	'	'	'	'	'	'	'	'
2016	149,428,000	'	'	'	'	'	'	'	'
2017	292,768,000	'	'	'	'	'	'	'	'
Thereafter	111,111,000	'	'	'	'	'	'	'	'
Other disclosures	'	'	'	'	'	'	'	'	'
Additional commitments	'	'	'	'	'	'	$50,000,000	'	'
Cash collateral maintained as a percentage of outstanding letters of credit	'	'	'	'	'	'	'	'	75.00%
Cash collateral required as a percentage of outstanding letters of credit under breach of certain financial covenants	'	'	'	'	'	'	100.00%	'	'
Letter of credit fee (as a percent)	'	'	'	'	'	'	0.50%	'	'
Number of letters of credit	'	'	'	'	'	'	'	4	'

Derivative_Financial_Instrumen2

Derivative Financial Instruments (Details)	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Oct. 31, 2013
	Three-way Collars	Three-way Collars	Three-way collars	Three-way collars	Three-way collars	Three-way collars	Three-way collars	Three-way collars	Put contracts
	Term October 2013 to December 2013	Term January 2014 to December 2014	Term October 2013 to December 2013	Term January 2014 to December 2014	Term October 2013 to December 2013	Term January 2014 to December 2014	Term October 2013 to December 2013	Term January 2014 to December 2014	Term January 2015 to December 2015
	MBbls	MBbls	MBbls	MBbls	MBbls	MBbls	MBbls	MBbls	MBbls
Derivative Financial Instruments	'	'	'	'	'	'	'	'	'
Volumes (in MBbl)	375	1,500	253	1,000	250	1,000	250	1,500	1,700
Weighted average deferred premium receivable/(payable) per Bbl	-4.82	-1.22	'	1.15	'	1.15	'	1.15	-3.78
Weighted average floor price per Bbl	95	85	87.5	85	90	88.09	90.08	90	85
Weighted average ceiling price per Bbl	105	115	115	115.01	115.39	110	115	113	'
Weighted average call price per Bbl	125	140	135	140	135	125	135	135	'

Derivative_Financial_Instrumen3

Derivative Financial Instruments (Details 2) (Interest Rate Swaps, USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013
Term October 2013 to December 2013	'
Derivative Financial Instruments	'
Weighted Average Notional Amount	$200,617
Weighted Average Fixed Rate (as a percent)	1.99%
Floating Rate	'6-month LIBOR
Term January 2014 to December 2014	'
Derivative Financial Instruments	'
Weighted Average Notional Amount	133,434
Weighted Average Fixed Rate (as a percent)	1.99%
Floating Rate	'6-month LIBOR
Term January 2015 to December 2015	'
Derivative Financial Instruments	'
Weighted Average Notional Amount	45,319
Weighted Average Fixed Rate (as a percent)	2.03%
Floating Rate	'6-month LIBOR
Term January 2016 to June 2016	'
Derivative Financial Instruments	'
Weighted Average Notional Amount	$12,500
Weighted Average Fixed Rate (as a percent)	2.27%
Floating Rate	'6-month LIBOR

Derivative_Financial_Instrumen4

Derivative Financial Instruments (Details 3) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Derivative instruments, Balance Sheet Location	'	'
Derivatives assets - current	$917,000	$1,061,000
Derivatives assets-long-term	1,583,000	'
Derivatives liabilities - current	-9,458,000	-20,377,000
Derivatives liabilities - long-term	-1,335,000	-3,226,000
Not designated as hedging instruments	'	'
Derivative instruments, Balance Sheet Location	'	'
Total	-8,293,000	-22,542,000
Commodity derivatives | Not designated as hedging instruments	'	'
Derivative instruments, Balance Sheet Location	'	'
Derivatives assets - current	917,000	1,061,000
Derivatives assets-long-term	1,583,000	'
Derivatives liabilities - current	-6,284,000	-17,005,000
Derivatives liabilities - long-term	-319,000	-659,000
Deferred premiums receivable related to commodity derivative contracts	1,100,000	0
Deferred premiums receivable related to commodity derivative contracts	600,000	'
Cash settlements made on commodity derivative contracts which were settled in the month subsequent to period end	0	3,400,000
Deferred premiums payable related to commodity derivative contracts	3,000,000	7,600,000
Deferred premiums payable related to commodity derivative contracts	600,000	2,400,000
Oil derivative contracts	'	'
Derivative instruments, Balance Sheet Location	'	'
Derivatives assets - current	900,000	'
Provisional Oil Sales	'	'
Derivative instruments, Balance Sheet Location	'	'
Derivatives assets - current	'	1,100,000
Interest rate contracts | Not designated as hedging instruments	'	'
Derivative instruments, Balance Sheet Location	'	'
Derivatives liabilities - current	-3,174,000	-3,372,000
Derivatives liabilities - long-term	($1,016,000)	($2,567,000)

Derivative_Financial_Instrumen5

Derivative Financial Instruments (Details 4) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Derivative instruments, Location of Gain/(Loss)	'	'	'	'
Amount of Gain/(Loss), derivatives not designated as hedging instruments	($8,457,000)	($13,966,000)	($5,874,000)	($13,552,000)
Gains expected to be reclassified from AOCI to interest expense	'	'	1,500,000	'
Commodity derivatives | Derivatives, net	'	'	'	'
Derivative instruments, Location of Gain/(Loss)	'	'	'	'
Amount of Gain/(Loss), derivatives not designated as hedging instruments	-7,585,000	-24,529,000	-386,000	-26,407,000
Commodity derivatives | Oil and gas revenue	'	'	'	'
Derivative instruments, Location of Gain/(Loss)	'	'	'	'
Amount of Gain/(Loss), derivatives not designated as hedging instruments	-554,000	11,494,000	-5,220,000	15,221,000
Interest rate contracts | Interest expense	'	'	'	'
Derivative instruments, Location of Gain/(Loss)	'	'	'	'
Amount of Gain/(Loss), derivatives not designated as hedging instruments	-318,000	-931,000	-268,000	-2,366,000
Derivatives in cash flow hedging relationships	'	'	'	'
Derivative instruments, Location of Gain/(Loss)	'	'	'	'
Total derivatives in cash flow hedging relationships	405,000	133,000	1,122,000	-295,000
Derivatives in cash flow hedging relationships | Interest rate contracts | Interest expense	'	'	'	'
Derivative instruments, Location of Gain/(Loss)	'	'	'	'
Amount of Gain/(Loss) reclassified from AOCI into earnings	$405,000	$133,000	$1,122,000	($295,000)

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (Recurring basis, USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Level 2	'	'
Liabilities:	'	'
Total fair value, net	($8,293)	($22,542)
Level 2 | Commodity derivatives	'	'
Assets:	'	'
Derivative asset, fair value	2,500	1,061
Liabilities:	'	'
Derivative liability, fair value	-6,603	-17,664
Level 2 | Interest rate derivatives	'	'
Liabilities:	'	'
Derivative liability, fair value	-4,190	-5,939
Total	'	'
Liabilities:	'	'
Total fair value, net	-8,293	-22,542
Total | Commodity derivatives	'	'
Assets:	'	'
Derivative asset, fair value	2,500	1,061
Liabilities:	'	'
Derivative liability, fair value	-6,603	-17,664
Total | Interest rate derivatives	'	'
Liabilities:	'	'
Derivative liability, fair value	($4,190)	($5,939)

Equitybased_Compensation_Detai

Equity-based Compensation (Details) (LTIP, USD $)	3 Months Ended		9 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Compensation agreement	'	'	'	'
Compensation expense recognized	$13.80	$19.40	$50.80	$58.20
Tax benefit	4.8	6.7	17.4	20.2
Tax shortfall	0	0	6.9	7.4
Weighted-Average Grant-Date Fair Value	'	'	'	'
Compensation expense not yet recognized	$144.70	'	$144.70	'
Weighted average period over which compensation expense is to be recognized	'	'	'2 years 2 months 12 days	'
Number of shares remaining available for grant	5,500,000	'	5,500,000	'
Service Vesting Restricted Stock Awards	'	'	'	'
Outstanding unvested awards activity	'	'	'	'
Outstanding at the beginning of the period (in shares)	'	'	9,898,000	'
Granted (in shares)	'	'	351,000	'
Forfeited (in shares)	'	'	-462,000	'
Vested (in shares)	'	'	-3,358,000	'
Outstanding at the end of the period (in shares)	6,429,000	'	6,429,000	'
Weighted-Average Grant-Date Fair Value	'	'	'	'
Outstanding at beginning of the period (in dollars per share)	'	'	$16.92	'
Granted (in dollars per share)	'	'	$10.73	'
Forfeited (in dollars per share)	'	'	$16.51	'
Vested (in dollars per share)	'	'	$17.26	'
Outstanding at the end of the period (in dollars per share)	$16.44	'	$16.44	'
Market/Service Vesting Restricted Stock Awards	'	'	'	'
Outstanding unvested awards activity	'	'	'	'
Outstanding at the beginning of the period (in shares)	'	'	3,534,000	'
Forfeited (in shares)	'	'	-93,000	'
Outstanding at the end of the period (in shares)	3,441,000	'	3,441,000	'
Weighted-Average Grant-Date Fair Value	'	'	'	'
Outstanding at beginning of the period (in dollars per share)	'	'	$12.93	'
Forfeited (in dollars per share)	'	'	$12.45	'
Outstanding at the end of the period (in dollars per share)	$12.94	'	$12.94	'
Market/Service Vesting Restricted Stock Awards | Minimum	'	'	'	'
Weighted-Average Grant-Date Fair Value	'	'	'	'
Granted (in dollars per share)	'	'	$6.70	'
Significant assumptions used to calculate fair values	'	'	'	'
Expected volatility (as a percent)	'	'	41.30%	'
Risk-free interest rate (as a percent)	'	'	0.50%	'
Market/Service Vesting Restricted Stock Awards | Maximum	'	'	'	'
Weighted-Average Grant-Date Fair Value	'	'	'	'
Granted (in dollars per share)	'	'	$13.57	'
Significant assumptions used to calculate fair values	'	'	'	'
Expected volatility (as a percent)	'	'	56.70%	'
Risk-free interest rate (as a percent)	'	'	1.10%	'
Other disclosures	'	'	'	'
Vesting percentage of the awards granted	'	'	100.00%	'
Service Vesting Restricted Stock Units	'	'	'	'
Outstanding unvested awards activity	'	'	'	'
Outstanding at the beginning of the period (in shares)	'	'	1,023,000	'
Granted (in shares)	'	'	1,512,000	'
Forfeited (in shares)	'	'	-133,000	'
Vested (in shares)	'	'	-225,000	'
Outstanding at the end of the period (in shares)	2,177,000	'	2,177,000	'
Weighted-Average Grant-Date Fair Value	'	'	'	'
Outstanding at beginning of the period (in dollars per share)	'	'	$10.59	'
Granted (in dollars per share)	'	'	$10.80	'
Forfeited (in dollars per share)	'	'	$10.53	'
Vested (in dollars per share)	'	'	$10.51	'
Outstanding at the end of the period (in dollars per share)	$10.75	'	$10.75	'
Market/Service Vesting Restricted Stock Units	'	'	'	'
Outstanding unvested awards activity	'	'	'	'
Outstanding at the beginning of the period (in shares)	'	'	825,000	'
Granted (in shares)	'	'	1,074,000	'
Forfeited (in shares)	'	'	-73,000	'
Outstanding at the end of the period (in shares)	1,826,000	'	1,826,000	'
Weighted-Average Grant-Date Fair Value	'	'	'	'
Outstanding at beginning of the period (in dollars per share)	'	'	$15.81	'
Granted (in dollars per share)	'	'	$15.44	'
Forfeited (in dollars per share)	'	'	$15.74	'
Outstanding at the end of the period (in dollars per share)	$15.60	'	$15.60	'
Market/Service Vesting Restricted Stock Units | Minimum	'	'	'	'
Weighted-Average Grant-Date Fair Value	'	'	'	'
Granted (in dollars per share)	'	'	$15.44	'
Significant assumptions used to calculate fair values	'	'	'	'
Expected volatility (as a percent)	'	'	53.00%	'
Risk-free interest rate (as a percent)	'	'	0.50%	'
Market/Service Vesting Restricted Stock Units | Maximum	'	'	'	'
Weighted-Average Grant-Date Fair Value	'	'	'	'
Granted (in dollars per share)	'	'	$15.81	'
Significant assumptions used to calculate fair values	'	'	'	'
Expected volatility (as a percent)	'	'	54.00%	'
Risk-free interest rate (as a percent)	'	'	0.70%	'
Other disclosures	'	'	'	'
Vesting percentage of the awards granted	'	'	200.00%	'

Income_Taxes_Details

Income Taxes (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Taxes	'	'	'	'
Income tax expense	$34,224	$25,923	$124,568	$64,730
Income (loss) before income taxes	-10,264	-10,327	29,358	-33,904
Effective tax rate (as a percent)	-333.00%	-251.00%	424.00%	-191.00%
Bermuda	'	'	'	'
Income Taxes	'	'	'	'
Income (loss) before income taxes	-5,880	-2,316	-19,320	-8,735
United States	'	'	'	'
Income Taxes	'	'	'	'
Income (loss) before income taxes	2,740	3,145	8,014	9,492
Effective tax rate (as a percent)	42.00%	43.00%	125.00%	116.00%
Foreign-other	'	'	'	'
Income Taxes	'	'	'	'
Income (loss) before income taxes	($7,124)	($11,156)	$40,664	($34,661)
Effective tax rate (as a percent)	'	'	0.00%	'
Statutory rate (as a percent)	'	'	0.00%	'
Ghana	'	'	'	'
Income Taxes	'	'	'	'
Effective tax rate (as a percent)	36.00%	39.00%	36.00%	37.00%

Net_Income_Loss_Per_Share_Deta

Net Income (Loss) Per Share (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerator:	'	'	'	'
Net income (loss)	($44,488)	($36,250)	($95,210)	($98,634)
Basic net income (loss) allocable to common shareholders	-44,488	-36,250	-95,210	-98,634
Diluted net income (loss) allocable to common shareholders	($44,488)	($36,250)	($95,210)	($98,634)
Weighted average number of shares used to compute net income (loss) per share:	'	'	'	'
Basic (in shares)	377,654,000	373,448,000	376,509,000	371,140,000
Diluted (in shares)	377,654,000	373,448,000	376,509,000	371,140,000
Net income (loss) per share:	'	'	'	'
Basic (in dollars per share)	($0.12)	($0.10)	($0.25)	($0.27)
Diluted (in dollars per share)	($0.12)	($0.10)	($0.25)	($0.27)
Outstanding restricted stock awards and restricted stock units excluded from the computations of diluted net income (loss) per share (in shares)	13,900,000	17,100,000	13,900,000	17,100,000

Commitments_and_Contingencies_1

Commitments and Contingencies (Details) (USD $)	1 Months Ended	9 Months Ended
	Jun. 30, 2013	Sep. 30, 2013
Offshore drilling rig contract commitments	'	'
Drilling rig contract period	'3 years	'
Initial rig rate per day	$600,000	'
Optional extension period	'3 years	'
Estimated future minimum commitments under Atwood Achiever drilling rig contract	'	'
2014	'	90,440,000
2015	'	217,175,000
2016	'	217,770,000
2017	'	126,140,000
Total	'	651,525,000
Rig rate per day	'	$595,000

Subsequent_Events_Details

Subsequent Events (Details) (USD $)	9 Months Ended		1 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Oct. 31, 2013	Oct. 31, 2013	Oct. 31, 2013	Oct. 31, 2013	Oct. 31, 2013	Oct. 31, 2013	Oct. 31, 2013	Oct. 31, 2013	Oct. 31, 2013
			Subsequent event	Subsequent event	Subsequent event	Subsequent event	Subsequent event	Subsequent event	Subsequent event	Subsequent event	Subsequent event
			WCTP Block	Farm-out agreements	Farm-out agreements	Farm-out agreements	Farm-out agreements	BP	BP	Cairn	Cairn
			Akasa Discovery	Essaouira Offshore Block	Foum Assaka Offshore Block	Tarhazoute Offshore Block	Cap Boujdour Contact Area	Farm-out agreements	Farm-out agreements	Farm-out agreements	Farm-out agreements
								Essaouira Offshore, Foum Assaka Offshore and Tarhazoute Offshore blocks	Essaouira Offshore, Foum Assaka Offshore and Tarhazoute Offshore blocks	Cap Boujdour Contact Area	Cap Boujdour Contact Area
								item	Maximum	item	Maximum
Subsequent events	'	'	'	'	'	'	'	'	'	'	'
Number of farm-out agreements	'	'	'	'	'	'	'	3	'	'	'
Number of blocks covered by farm-out agreements	'	'	'	'	'	'	'	3	'	'	'
Number of exploration wells in each block for which our share of costs will be paid for by a third party	'	'	'	'	'	'	'	1	'	'	'
Number of exploration wells for which a third party will pay a disproportionate amount	'	'	'	'	'	'	'	'	'	1	'
Spending per well by third party for first exploration well	'	'	'	'	'	'	'	'	$120,000,000	'	'
Spending by third party for seismic and an exploration well	'	'	'	'	'	'	'	'	'	'	125,000,000
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%	'	'	'
Spending per well by third party in the event of drilling a second exploration well	'	'	'	'	'	'	'	'	120,000,000	'	'
Amount of past costs to be paid by third party	'	'	'	'	'	'	'	36,300,000	'	'	'
Participating interests (as a percent)	'	'	'	30.00%	29.93%	30.00%	55.00%	'	'	'	'
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	'
Spending per well by third party for each appraisal well	'	'	'	'	'	'	'	'	'	'	100,000,000
Amount of our future costs to be paid for by third party	'	'	'	'	'	'	'	'	'	12,300,000	'
Impaired costs associated with the Akasa-2A appraisal well	98,912,000	19,357,000	11,500,000	'	'	'	'	'	'	'	'
Estimated additional related well costs	'	'	$8,900,000	'	'	'	'	'	'	'	'