Cobalt International Energy 10-K 23 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
In Billions, except Share data, unless otherwise specified	Dec. 31, 2014	Jun. 30, 2014
Document and Entity Information
Entity Registrant Name	Cobalt International Energy, Inc.
Entity Central Index Key	1471261
Document Type	10-K
Document Period End Date	31-Dec-14
Amendment Flag	FALSE
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float		$5.80
Entity Common Stock, Shares Outstanding	411,296,254
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$258,721	$192,460
Joint interest and other receivables	59,974	124,639
Prepaid expenses and other current assets	14,497	55,857
Inventory	94,674	74,768
Short-term restricted funds	45,062	200,339
Short-term investments	1,530,206	1,319,380
Total current assets	2,003,134	1,967,443
Property, plant, and equipment:
Oil and gas properties, successful efforts method of accounting, net of accumulated depletion of $0	1,920,979	1,464,383
Other property and equipment, net of accumulated depreciation and amortization of $8,977 and $4,394, as of December 31, 2014 and 2013, respectively	11,382	11,892
Total property, plant, and equipment, net	1,932,361	1,476,275
Long-term restricted funds	105,051	104,496
Long-term investments	326,047	14,661
Deferred income taxes	30,334	17,061
Other assets	53,936	53,737
Total assets	4,450,863	3,633,673
Current liabilities:
Trade and other accounts payable	8,010	131,428
Accrued liabilities	214,972	143,459
Short-term contractual obligations	50,285	49,019
Deferred income taxes	30,334	17,061
Total current liabilities	303,601	340,967
Long-term debt	1,928,528	1,035,980
Long-term contractual obligations	101,945	124,901
Other long-term liabilities	2,523	2,679
Total long-term liabilities	2,032,996	1,163,560
Stockholders' Equity:
Common stock, $0.01 par value per share; 2,000,000,000 shares authorized 408,505,079 and 406,949,839 issued and outstanding as of December 31, 2014 and 2013, respectively	4,085	4,069
Additional paid-in capital	4,137,803	3,641,936
Accumulated deficit during the development stage	-2,027,622	-1,516,859
Total stockholders' equity	2,114,266	2,129,146
Total liabilities and stockholders' equity	$4,450,863	$3,633,673

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Consolidated Balance Sheets
Oil and gas properties, successful efforts method of accounting, accumulated depletion (in dollars)	$0	$0
Other property and equipment, accumulated depreciation and amortization (in dollars)	$8,977	$4,394
Common stock, par value (in dollars per share)	$0.01	$0.01
Common stock, shares authorized	2,000,000,000	2,000,000,000
Common stock, shares issued	408,505,079	406,949,839
Common stock, shares outstanding	408,505,079	406,949,839

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Consolidated Statements of Operations
Oil and gas revenue	$0	$0	$0
Operating costs and expenses:
Seismic and exploration	85,567	74,213	61,583
Dry hole expense and impairment	236,930	351,050	134,085
General and administrative	114,860	105,547	87,963
Depreciation and amortization	4,584	1,874	1,197
Total operating costs and expenses	441,941	532,684	284,828
Operating income (loss)	-441,941	-532,684	-284,828
Other income (expense):
Gain (loss) on sale of assets	-12	2,993
Interest income	5,958	6,043	5,041
Interest expense	-74,768	-65,376	-3,212
Total other income (expense)	-68,822	-56,340	1,829
Net income (loss) before income tax	-510,763	-589,024	-282,999
Income tax expense	0	0	0
Net income (loss)	($510,763)	($589,024)	($282,999)
Basic and diluted income (loss) per common share (in dollars per share)	($1.25)	($1.45)	($0.70)
Basic and diluted weighted average common shares outstanding (in shares)	407,116,144	406,839,997	403,356,174

Consolidated_Statements_of_Cha

Consolidated Statements of Changes in Stockholders' Equity (USD $)	Common Stock	Additional Paid-in Capital	Accumulated Deficit During Development Stage	Total
In Thousands
Balance at Dec. 31, 2011	$3,875	$2,719,875	($644,836)	$2,078,914
Common stock issued at public offering, net of costs	181	489,128		489,309
Common stock issued for restricted stock and stock options	10	-10
Equity based compensation		22,410		22,410
Exercise of stock options		338		338
Common stock withheld for taxes on equity based compensation		-170		-170
Equity portion of debt, net of allocated costs		381,416		381,416
Net income (loss)			-282,999	-282,999
Balance at Dec. 31, 2012	4,066	3,612,987	-927,835	2,689,218
Common stock issued for restricted stock and stock options	3	-3
Equity based compensation		28,754		28,754
Exercise of stock options		198		198
Net income (loss)			-589,024	-589,024
Balance at Dec. 31, 2013	4,069	3,641,936	-1,516,859	2,129,146
Common stock issued for restricted stock and stock options	16	-16
Equity based compensation		31,742		31,742
Exercise of stock options		33		33
Common stock withheld for taxes on equity based compensation		-630		-630
Equity portion of debt, net of allocated costs		464,738		464,738
Net income (loss)			-510,763	-510,763
Balance at Dec. 31, 2014	$4,085	$4,137,803	($2,027,622)	$2,114,266

Consolidated_Statements_of_Cha1

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical)	Dec. 31, 2014	Dec. 31, 2012
Consolidated Statements of Changes in Partners' Capital and Stockholders' Equity
Interest rate (as a percent)	3.13%	2.63%

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows provided from operating activities
Net income (loss)	($510,763)	($589,024)	($282,999)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Depreciation and amortization	4,584	1,874	1,197
Dry hole expense and impairment	236,930	351,050	134,085
Gain on sale of assets		-2,993
Equity based compensation	31,742	28,754	22,410
Amortization of premium (accretion of discount) on investments	18,159	21,955	15,091
Amortization of debt discount	71,330	46,847
Changes in operating assets and liabilities:
Joint interest and other receivables	64,679	-62,967	-1,518
Inventory	-20,906	-10,052	-29,237
Prepaid expense and other current assets	41,359	-31,915	-1,726
Deferred charges	15,980	-32,753	-10,985
Trade and other accounts payable	-64,369	63,552	-3,309
Accrued liabilities and other	46,749	-696	16,594
Net cash provided by (used in) operating activities	-64,526	-216,368	-140,397
Cash flows from investing activities
Capital expenditures for oil and gas properties	-70,639	-80,439	-142,841
Capital expenditures for other property and equipment	-4,074	-8,483	-5,139
Exploration wells drilling in process	-678,017	-581,194	-329,534
Proceeds from sale of oil and gas properties		3,006
Change in restricted funds	43,667	180,729	29,573
Proceeds from maturity of investment securities	1,700,123	1,366,977	1,082,876
Purchase of investment securities	-2,129,453	-1,896,591	-1,199,696
Net cash provided by (used in) investing activities	-1,138,393	-1,015,995	-564,761
Cash flows from financing activities
Proceeds from public offerings, net of costs			489,309
Proceeds from debt offering, net of costs	1,269,778	-1,190	1,348,950
Proceeds from exercise of stock options	33	198	338
Payments for common stock withheld for taxes on equity based compensation	-631		-170
Net cash provided by (used in) financing activities	1,269,180	-992	1,838,427
Net increase (decrease) in cash and cash equivalents	66,261	-1,233,355	1,133,269
Cash and cash equivalents, beginning of period	192,460	1,425,815	292,546
Cash and cash equivalents, end of period	258,721	192,460	1,425,815
Cash paid for interest	56,764	34,615
Non-Cash Disclosures
Changes in accrued capital expenditures	-56,129	58,769	-105,802
Transfer of investment securities to and from restricted funds	$112,434	$26	$178,830

Summary_of_Significant_Account

Summary of Significant Accounting Policy	12 Months Ended
	Dec. 31, 2014
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	1. Summary of Significant Accounting Policies
	Description of Operations
	Cobalt International Energy, Inc. (the "Company") is an independent exploration and production company with operations in the deepwater U.S. Gulf of Mexico and offshore Angola and Gabon in West Africa.
	Effective January 1, 2015, Cobalt International Energy, L.P. (the "Partnership"), an indirect wholly-owned subsidiary of the Company, assigned its ownership interest in the oil and gas leases, wells, production facilities and other assets and agreements associated with the Company's Heidelberg development to Cobalt GOM #1 LLC, an indirect wholly-owned subsidiary of the Company.
	The terms "Company," "Cobalt," "we," "us," "our," "ours," and similar terms refer to Cobalt International Energy, Inc. unless the context indicates otherwise.
	Basis of Presentation
	At December 31, 2014, the accompanying consolidated financial statements include the accounts of the Company and the Partnership. Prior to the effective date of a corporate reorganization, both entities were under common control arising from common direct or indirect ownership of each. The transfer of the Partnership interests to the Company represented a reorganization of entities under common control and was accounted for at historical cost.
	Recently Issued Accounting Standards
	In June 2014, the Financial Accounting Standards Board (the "FASB") amended Accounting Standard Codification Topic No. 915, Development Stage Entities (the "ASC Topic 915"), to remove the definition of a development stage entity from the Master Glossary of the ASC, thereby removing the financial reporting distinction between development stage entities and other reporting entities. The amendments eliminate the requirements for development stage entities to (1) present inception-to-date information in the statements of income, cash flows, and shareholder equity, (2) label the financial statements as those of a development stage entity, (3) disclose a description of the development stage activities in which the entity is engaged, and (4) disclose in the first year in which the entity is no longer a development stage entity that in prior years it had been in the development stage.
	These amendments and the other remaining disclosure requirements of the ASC Topic 915 should be applied retrospectively. For public business entities, ASC Topic 915 is effective for annual reporting periods beginning after December 15, 2014, and interim periods therein. Early application of ASC Topic 915 is permitted for any annual reporting period or interim period for which the entity's financial statements have not yet been issued or made for issuance. Upon adoption, entities will no longer present or disclose any information required by the ASC Topic 915. The Company elected to apply ASC Topic 915 early effective in the Form 10-Q for the quarter ended June 30, 2014 and other reports thereafter.
	Use of Estimates
	The preparation of financial statements in conformity with United States generally accepted accounting principles ("GAAP") requires the Company to make estimates and assumptions that affect the reported amounts of assets including proved reserves and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Significant estimates the Company makes include (a) accruals related to expenses, (b) assumptions used in estimating fair value of equity based awards and the fair value of the liability component of the convertible senior notes and (c) assumptions used in impairment testing. Although the Company believes these estimates are reasonable, actual results could differ from these estimates.
	Fair Value Measurements
	The fair values of the Company's cash and cash equivalents, joint interest and other receivables, restricted funds and investments approximate their carrying amounts due to their short-term duration. The hierarchy below lists three levels of fair value based on the extent to which inputs used in measuring fair value are observable in the market. The Company categorizes each of its fair value measurements as applicable to one of these three levels based on the lowest level input that is significant to the fair value measurement in its entirety. The levels are:
	Level 1—Quoted prices in active markets that are accessible at the measurement date for identical assets or liabilities. This category includes the Company's cash and money market funds.
	Level 2—Quoted prices in non-active markets or in active markets for similar assets or liabilities, and inputs other than quoted prices that are observable, for the asset or liability, either directly or indirectly for substantially the full contractual term of the asset or liability being measured. This category includes the Company's U.S. Treasury bills, U.S. Treasury notes, U.S. Government agency securities, commercial paper, corporate bonds and certificates of deposits.
	Level 3—Inputs that are generally unobservable and typically reflect management's estimate of assumptions that market participants would use in pricing the asset or liability. The Company does not currently have any financial instruments categorized as Level 3.
	Revenue Recognition
	The Company will follow the "sales" (or cash) method of accounting for oil and gas revenues. Under this method, the Company will recognize revenues on the volumes sold. The volumes sold may be more or less than the volumes to which the Company is entitled based on its ownership interest in the property. These differences result in a condition known in the industry as a production imbalance. For the years ended December 31, 2014, 2013 and 2012, no revenues have been recognized in these consolidated financial statements.
	Cash and Cash Equivalents
	Cash and cash equivalents consist of demand deposits and funds invested in highly liquid instruments with maturities of three months or less from the date of purchase. Demand deposits typically exceed federally insured limits; however, the Company periodically assesses the financial condition of the institutions where these funds are held as well as the credit ratings of the issuers of the highly liquid instruments and believes that the credit risk is minimal.
	Restricted Funds
	Restricted funds consist of collateral for letters of credit relating to our operations offshore Angola.
	Investments
	The Company's policy on accounting for its investments, which consist entirely of debt securities, is based on the accounting guidance relating to "Accounting for Certain Investments in Debt and Equity Securities." The Company considers all highly liquid interest-earning investments with a maturity of three months or less at the date of purchase to be cash equivalents. Investments with original maturities of greater than three months and remaining maturities of less than one year are classified as short-term investments. Investments with maturities beyond one year are classified as long-term investments. The debt securities are carried at amortized costs and classified as held-to-maturity securities as the Company has the positive intent and ability to hold them until they mature. The net carrying value of held-to-maturity securities is adjusted for amortization of premiums and accretion of discounts to maturity over the life of the securities. Held-to-maturity securities are stated at amortized cost, which approximates fair market value as of December 31, 2014 and 2013. Income related to these securities is reported as a component of interest income in the Company's consolidated statement of operations. See Note 6—Investments.
	Investments are considered to be impaired when a decline in fair value is determined to be other-than-temporary. The Company conducts a regular assessment of its debt securities with unrealized losses to determine whether securities have other-than-temporary impairment ("OTTI"). This assessment considers, among other factors, the nature of the securities, credit rating or financial condition of the issuer, the extent and duration of the unrealized loss, market conditions and whether the Company intends to sell or whether it is more likely than not that the Company will be required to sell the debt securities. As of December 31, 2014 and 2013, the Company has no OTTI in its debt securities.
	Capitalized Interest
	For exploration and development projects that have not commenced production, interest is capitalized as part of the historical cost of developing and constructing assets. Capitalized interest is determined by multiplying the Company's weighted-average borrowing cost on debt by the average amount of qualifying costs incurred. Once an asset subject to interest capitalization is completed and placed in service, the associated capitalized interest is expensed through depreciation or impairment. See Note 8—Property, Plant, and Equipment and Note 10—Long-term Debt.
	Joint Interest and Other Receivables
	Joint interest and other receivables result primarily from billing shared costs under the respective operating agreements to the Company's partners. These receivables are usually settled within 30 days of the invoice date.
	Property, Plant, and Equipment
	The Company uses the "successful efforts" method of accounting for its oil and gas properties. Acquisition costs for unproved leasehold properties and costs of drilling exploration wells are capitalized pending determination of whether proved reserves can be attributed to the areas as a result of drilling those wells. Under the successful efforts method of accounting, proved leasehold costs are capitalized and amortized over the proved developed and undeveloped reserves on a units-of-production basis. Successful drilling costs, costs of development and developmental dry holes are capitalized and amortized over the proved developed reserves on a units-of-production basis. Significant unproved leasehold costs are capitalized and are not amortized, pending an evaluation of their exploration potential. Unproved leasehold costs are assessed periodically to determine if an impairment of the cost of individual properties has occurred. Factors taken into account for impairment analysis include results of the technical studies conducted, lease terms and management's future exploration plans. The cost of impairment is charged to expense in the period in which it occurs. Costs incurred for exploration dry holes, geological and geophysical work (including the cost of seismic data), and delay rentals are charged to expense as incurred. Costs of other property and equipment are depreciated on a straight-line basis based on their respective useful lives.
	Asset Retirement Obligations
	The Company currently does not have any oil and natural gas production or any legal obligations to incur decommissioning costs. Should such production occur in the future, the Company expects to have significant obligations under its lease agreements and federal regulation to remove its equipment and restore land or seabed at the end of oil and natural gas production operations. These asset retirement obligations are primarily associated with plugging and abandoning wells and removing and disposing of offshore oil and natural gas platforms. Estimating the future restoration and removal cost is difficult and requires the Company to make estimates and judgments because most of the removal obligations are many years in the future and contracts and regulation often have vague descriptions of what constitutes removal. Asset removal technologies and cost are constantly changing, as are regulatory, political, environmental, safety and public relations considerations. Pursuant to the accounting guidance relating to "Asset Retirement Obligations", the Company is required to record a separate liability for the estimated fair value of its asset retirement obligations, with an offsetting increase to the related oil and natural gas properties representing asset retirement costs on its balance sheet. The cost of the related oil and natural gas asset, including the asset retirement cost, is depreciated over the useful life of the asset. The estimated fair value of asset retirement obligations is measured by reference to the expected future cash outflows required to satisfy the retirement obligation discounted at the Company's credit-adjusted risk-free interest rate. Accretion expense is recognized over time as the discounted liability is accreted to its expected settlement value.
	Inherent to the present value calculation are numerous estimates, assumptions and judgments, including the ultimate settlement amounts, inflation factors, credit adjusted risk-free rates, timing of settlement and changes in the legal, regulatory, environmental and political environments. To the extent future revisions to these assumptions impact the present value of the abandonment liability, the Company will make corresponding adjustments to both the asset retirement obligation and the related oil and natural gas property asset balance. Increases in the discounted abandonment liability and related oil and natural gas assets resulting from the passage of time will be reflected as additional accretion and depreciation expense in the consolidated statements of operations.
	Inventory
	Inventories consist of various tubular products that are used in the Company's drilling programs. The products are stated at the average cost. Cost is determined using a weighted average method comprised of the purchase price and other directly attributable costs.
	Income Taxes
	The Company applied the liability method of accounting for income taxes in accordance with accounting guidance related to "Income Taxes" as clarified by "Accounting for Uncertainty in Income Taxes." Under this method, deferred tax assets and liabilities are determined by applying tax rates in effect at the end of a reporting period to the cumulative temporary differences between the tax bases of assets and liabilities and their reported amounts in the financial statements. Since the Company currently has no production activities and there can be no assurance that the Company will generate any earnings or any specific level of earnings in future years, the Company has established a valuation allowance that equals its net deferred tax assets. See Note 16.
	Equity-Based Compensation
	The Company accounts for stock-based compensation at fair value. The Company grants various types of stock-based awards including stock options, restricted stock and performance-based awards. The fair value of stock option awards is determined using the Black-Scholes-Merton option-pricing model. For restricted stock awards with market conditions, the fair value of the awards is measured using the asset-or-nothing option pricing model. Restricted stock awards without market conditions and the performance-based awards are valued using the market price of the Company's common stock on the grant date. The Company records compensation cost, net of estimated forfeitures, on a straight-line basis for stock-based compensation awards over the requisite service period except for performance-based awards. For performance-based awards, compensation cost is recognized over the requisite service period as and when the Company determines that the achievement of the performance condition is probable, using the per-share fair value measured at grant date. See Note 14.
	Earnings (Loss) Per Share
	Basic income (loss) per share was calculated by dividing net income or loss applicable to common shares by the weighted average number of common shares outstanding during the periods presented. The calculation of diluted income (loss) per share should include the potential dilutive impact of non-vested restricted shares, non-vested restricted stock units, outstanding stock options, the 2.625% convertible senior notes due 2019 and the 3.125% convertible senior notes due 2024, during the period, unless their effect is anti-dilutive. For the year ended December 31, 2014, 5,997,374 shares of non-vested restricted stock, non-vested restricted stock units, outstanding stock options, the 2.625% convertible senior notes due 2019 and the 3.125% convertible senior notes due 2024, were excluded from the diluted income (loss) per share because they are anti-dilutive. For the year ended December 31, 2013, 6,735,046 shares of non-vested restricted stock, non-vested restricted stock units, outstanding stock options and the 2.625% convertible senior notes due 2019 were excluded from the diluted income (loss) per share because they are anti-dilutive. For the year ended December 31, 2012, 5,617,697 shares of non-vested restricted stock, non-vested restricted stock units and outstanding stock options were excluded from the diluted income (loss) per share because they are anti-dilutive.
	Operating Costs and Expenses
	Expenses consist primarily of the costs of acquiring and processing of geological and geophysical data, exploration, and appraisal drilling expenses, consultants, telecommunications, payroll and benefit costs, information system and legal costs, office rent, contract costs, and bookkeeping and audit fees.

Cash_and_Cash_Equivalents

Cash and Cash Equivalents	12 Months Ended
	Dec. 31, 2014
Cash and Cash Equivalents.
Cash and Cash Equivalents	2. Cash and Cash Equivalents
	As of December 31, 2014 and 2013, cash and cash equivalents consisted of the following:
			December 31,		December 31,
			2014		2013
			($ in thousands)
	Cash at banks		$	57,750	$	82,428
	Money market funds			122,218		75,039
	Held-to-maturity securities(1)			78,753		34,993
			$	258,721	$	192,460
	-1	These securities mature three months or less from date of purchase.

Restricted_Funds

Restricted Funds	12 Months Ended
	Dec. 31, 2014
Restricted Funds
Restricted Funds	3. Restricted Funds
	Restricted funds consisted of the following:
			December 31,		December 31,
			2014		2013
			($ in thousands)
	Short-term:
	Collateral on letters of credit for Angola		$	45,062	$	200,339
			$	45,062	$	200,339
	Long-term:
	Collateral on letters of credit for Angola		$	105,051	$	104,496
			$	105,051	$	104,496
	Total restricted funds(1)		$	150,113	$	304,835
	-1	As of December 31, 2014 and 2013, $150.1 million and $304.8 million, respectively, was held in a collateral account established to secure letters of credit issued in support of the Company's contractually agreed work program obligations on Blocks 9, 20 and 21 offshore Angola. During the year ended December 31, 2014, restricted funds of $155.0 million were released to the Company in connection with completion of a portion of the agreed work program obligations on Block 20 and 21 offshore Angola. As of December 31, 2014, $45.1 million was reclassified from long-term restricted funds to short-term restricted funds in connection with the completion of a portion of the Company's agreed work program obligations on Block 9 and 21 offshore Angola. On February 5, 2015, restricted funds totaling $45.1 million were released to the Company in connection with completion of a portion of the work program obligations on Block 9 and completion of the remaining work program obligations on Block 21. The Block 21 letter of credit was therefore reduced to zero and cancelled effective February 10, 2015. As of December 31, 2014 and 2013, the collateral in this account was invested in U.S. Treasury bills and Treasury notes purchased at discounts and at premiums, respectively, resulting in a net carrying value of $150.1 million and $304.8 million, respectively. The contractual maturities of these securities are within one year.

Joint_Interests_and_Other_Rece

Joint Interests and Other Receivables	12 Months Ended
	Dec. 31, 2014
Joint Interest and Other Receivables
Joint Interest and Other Receivables	4. Joint Interests and Other Receivables
	Joint interest and other receivables result primarily from billing shared costs under the respective operating agreements to the Company's partners. These are usually settled within 30 days of the invoice date. As of December 31, 2014 and 2013, the balance in joint interest and other receivables consisted of the following:
		December 31,		December 31,
		2014		2013
		($ in thousands)
	Partners in the U.S. Gulf of Mexico	$	3,274	$	68,664
	Partners in West Africa		46,312		46,897
	Accrued interest on investment securities		7,663		5,632
	Other		2,725		3,446
		$	59,974	$	124,639

Prepaid_Expenses_and_Other_Cur

Prepaid Expenses and Other Current Assets	12 Months Ended
	Dec. 31, 2014
Prepaid Expenses and Other Current Assets
Prepaid Expenses and Other Current Assets	5. Prepaid Expenses and Other Current Assets
	As of December 31, 2014 and 2013, prepaid expenses and other current assets consisted of the following:
			December 31,		December 31,
			2014		2013
			($ in thousands)
	Prepaid expenses:
	Prepaid expenses(1)		$	6,273	$	37,796
	Other current assets:
	Cash advance to joint venture partner(2)			—		9,685
	Rig mobilization, regulatory and other related costs(3)			8,224		8,376
			$	14,497	$	55,857
	-1	As of December 31, 2014, prepaid expenses include $6.3 million of the prepaid and unamortized portion of payments made for software licenses, related maintenance fees and insurance. As of December 31, 2013, prepaid expenses include $11.5 million of the prepaid and unamortized portion of payments made for software licenses, related maintenance fees, insurance and $26.3 million of prepaid costs associated with the Ensco drilling rig contract. The drilling rig contract terminated in January 2014 and upon receipt and application of prepaid amounts against the final invoice from Ensco, any remaining balance of the prepayment was refunded to the Company.
	-2	As of December 31, 2013, the $9.7 million in other current assets relates to payment of cash calls made to our joint interest partner, Total Gabon, for operating costs to drill the Diaman #1B exploration well. This prepayment was applied against the joint interest bills upon receipt from Total Gabon as of December 31, 2014.
	-3	As of December 31, 2014 and 2013, the $8.2 million and $8.4 million, respectively, in other current assets relates to the short-term portion of the mobilization and regulatory acceptance testing costs associated with the SSV Catarina drilling rig and the Rowan Reliance drilling rig.

Investments

Investments	12 Months Ended
	Dec. 31, 2014
Investments
Investments	6. Investments
	The Company's investments in held-to-maturity securities which are recorded at amortized cost and approximate fair market value were as follows as of December 31, 2014 and 2013:
		December 31,		December 31,
		2014		2013
		($ in thousands)
	U.S. Treasury bills	$	46,064	$	304,834
	U.S. Treasury notes		104,049		—
	Corporate securities		1,321,261		856,002
	Commercial paper		483,534		408,033
	U.S. Agency securities		24,996		—
	Certificates of deposit		105,215		105,000
	Total	$	2,085,119	$	1,673,869
	The Company's consolidated balance sheet included the following held-to-maturity securities:
		December 31,		December 31,
		2014		2013
		($ in thousands)
	Cash and cash equivalents	$	78,753	$	34,993
	Short-term investments		1,530,206		1,319,380
	Short-term restricted funds		45,062		200,339
	Long-term restricted funds		105,051		104,496
	Long-term investments		326,047		14,661
		$	2,085,119	$	1,673,869
	The contractual maturities of these held-to-maturity securities as of December 31, 2014 and 2013 were as follows:
		December 31, 2014				December 31, 2013
		Carrying		Estimated		Carrying		Estimated
		Value		Fair Value		Value		Fair Value
		($ in thousands)
	Within 1 year	$	1,759,072	$	1,759,072	$	1,659,208	$	1,659,208
	After 1 year		326,047		326,047		14,661		14,661
		$	2,085,119	$	2,085,119	$	1,673,869	$	1,673,869

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2014
Fair Value Measurements
Fair Value Measurements	7. Fair Value Measurements
	The following tables summarize the Company's significant financial instruments as categorized by the fair value measurement hierarchy:
			Level 1				Level 2
			Carrying		Fair		Carrying		Fair		Balance as of
			Value		Value(1)		Value		Value(1)		December 31,
											2014
			($ in thousands)
	Cash and cash equivalents:
	Cash		$	57,750	$	57,750	$	—	$	—	$	57,750
	Money market funds			122,218		122,218						122,218
	Commercial paper			—		—		70,524		70,524		70,524
	Corporate bonds			—		—		8,229		8,229		8,229
	Subtotal			179,968		179,968		78,753		78,753		258,721
	Short-term restricted funds:
	U.S. Treasury bills			—		—		45,062		45,062		45,062
	Subtotal			—		—		45,062		45,062		45,062
	Short-term investments:
	U.S. Agency securities			—		—		24,996		24,996		24,996
	Corporate bonds			—		—		986,985		986,985		986,985
	Commercial paper			—		—		413,010		413,010		413,010
	Certificates of deposits			—		—		105,215		105,215		105,215
	Subtotal			—		—		1,530,206		1,530,206		1,530,206
	Long-term restricted funds:
	U.S. Treasury bills			—		—		1,002		1,002		1,002
	U.S. Treasury notes			—		—		104,049		104,049		104,049
	Subtotal			—		—		105,051		105,051		105,051
	Long-term investments:
	Corporate bonds			—		—		326,047		326,047		326,047
	Subtotal			—		—		326,047		326,047		326,047
	Total		$	179,968	$	179,968	$	2,085,119	$	2,085,119	$	2,265,087
			Level 1				Level 2
			Carrying		Fair		Carrying		Fair		Balance as of
			Value		Value(1)		Value		Value(1)		December 31,
											2013
			($ in thousands)
	Cash and cash equivalents:
	Cash		$	82,428	$	82,428	$	—	$	—	$	82,428
	Money market funds			75,039		75,039		—		—		75,039
	Commercial paper			—		—		9,993		9,993		9,993
	Certificate of deposits			—		—		25,000		25,000		25,000
	Subtotal			157,467		157,467		34,993		34,993		192,460
	Short-term restricted funds:
	U.S. Treasury notes			—		—		200,339		200,339		200,339
	Subtotal			—		—		200,339		200,339		200,339
	Short-term investments:
	Corporate bonds			—		—		848,307		848,307		848,307
	Commercial paper			—		—		391,073		391,073		391,073
	Certificates of deposits			—		—		80,000		80,000		80,000
	Subtotal			—		—		1,319,380		1,319,380		1,319,380
	Long-term restricted funds:
	U.S. Treasury notes			—		—		104,496		104,496		104,496
	Subtotal			—		—		104,496		104,496		104,496
	Long-term investments:
	Commercial paper			—		—		6,967		6,967		6,967
	Corporate bonds			—		—		7,694		7,694		7,694
	Subtotal			—		—		14,661		14,661		14,661
	Total		$	157,467	$	157,467	$	1,673,869	$	1,673,869	$	1,831,336
	-1	As of December 31, 2014 and 2013, the Company did not record any OTTI on these assets.

Property_Plant_and_Equipments

Property, Plant, and Equipments	12 Months Ended
	Dec. 31, 2014
Property, Plant, and Equipment
Property, Plant, and Equipment	8. Property, Plant, and Equipment
	Property, plant, and equipment is stated at cost less accumulated depreciation/amortization and consisted of the following:
			Estimated		December 31,			December 31,
			Useful Life		2014			2013
			(Years)
					($ in thousands)
	Oil and Gas Properties:
	Proved properties:
	Well and development costs				$	183,221		$	92,579
	Total proved properties					183,221			92,579
	Unproved properties:
	Oil and gas leasehold					762,518			754,894
	Less: accumulated valuation allowance					(211,224	)		(160,913	)
						551,294			593,981
	Exploration wells in process					1,186,464			777,823
	Total unproved properties					1,737,758			1,371,804
	Total oil and gas properties, net					1,920,979			1,464,383
	Other Property and Equipment:
	Computer equipment and software		3			5,672			5,115
	Office equipment and furniture		3 - 5			2,139			2,132
	Vehicles		3			265			265
	Leasehold improvements		3 - 10			2,488			2,456
	Running tools and equipment		3			9,795			6,318
						20,359			16,286
	Less: accumulated depreciation and amortization					(8,977	)		(4,394	)
	Total other property and equipment, net					11,382			11,892
	Property, plant, and equipment, net				$	1,932,361		$	1,476,275
	The Company recorded $4.6 million, $1.9 million, and $1.2 million of depreciation and amortization expense for the years ended December 31, 2014, 2013 and 2012, respectively.
	Proved Oil and Gas Properties
	The Heidelberg project was formally sanctioned for development in mid-2013. As a result of the project sanction, the Company reclassified its Heidelberg exploration well costs to proved property well and development costs and these costs will be amortized when the related proved developed reserves are produced. As of December 31, 2014, the well and development costs consist of $51.1 million relating to exploration well costs for the Heidelberg #1 exploration well, Heidelberg #3 appraisal well, Heidelberg #4 and Heidelberg #6 development wells and $132.1 million for costs associated with field development. As of December 31, 2013, the well and development costs consist of $31.6 million relating to exploration well costs for the Heidelberg #1 exploration well and Heidelberg #3 appraisal well and $61.0 million for costs associated with field development.
	Unproved Oil and Gas Properties
	As of December 31, 2014 and 2013, the Company has the following unproved property acquisition costs, net of valuation allowance on the consolidated balance sheets:
			December 31,			December 31,
			2014			2013
			($ in thousands)
	U.S. Gulf of Mexico:
	Individual oil and gas leaseholds with carrying value greater than $1 million		$	320,731		$	328,128
	Individual oil and gas leaseholds with carrying value less than $1 million			83,916			68,895
				404,647			397,023
	Accumulated valuation allowance & impairment			(208,724	)		(160,913	)
				195,923			236,110
	West Africa:
	Blocks 9, 20 and 21 offshore Angola			355,876			355,876
	Diaba Block offshore Gabon			1,995			1,995
				357,871			357,871
	Accumulated impairment			(2,500	)		—
				355,371			357,871
	Total oil and gas leasehold		$	551,294		$	593,981
	As of December 31, 2014 and 2013, the Company has $353.4 million and $355.9 million, respectively, of unproved property acquisition costs, net of valuation allowance for impairment, relating to its 40% working interest each in Blocks 9, 20 and 21 offshore Angola and $2.0 million of unproved property acquisition costs relating to its 21.25% working interest in the Diaba Block, offshore Gabon. On December 20, 2011, the Company acquired a 40% working interest in Block 20 offshore Angola for a consideration of $347.1 million, of which $337.1 million is contractually scheduled to be paid over five years commencing in January 2012. As of December 31, 2014, the remaining unpaid balance of $128.6 million was accrued in short-term and long-term contractual obligations. See Note 11—Contractual Obligations.
	As of December 31, 2014 and 2013, the Company also has $195.9 million and $236.1 million, respectively, net of valuation allowance for impairment, of unproved property acquisition costs relating to its U.S. Gulf of Mexico properties. In June and July of 2014, the Company paid a total consideration of $27.8 million for the acquisition of ownership interests in unproved oil and gas properties in the deepwater U.S. Gulf of Mexico. On February 26, 2013, the Company executed a Purchase and Sale agreement (the "PSA") to sell its ownership interests on an unproved oil and gas property on Mississippi Canyon Block 209 for a total consideration of $5.6 million. The Company received $1.5 million at closing and an additional $1.5 million in September 2013 when the buyer commenced operations on the property. Pursuant to the terms and conditions of the PSA, the Company will receive the remaining $2.6 million contingent upon the purchaser's commencement of production on this property in the future. For the year ended December 31, 2013, the Company recognized a gain of $3.0 million on the sale of assets as a result of this transaction. During the year ended December 31, 2013, the Company paid a total consideration of $37.6 million for the acquisition of ownership interests in unproved oil and gas properties on Garden Banks Block 822, Mississippi Canyon Block 605 and Walker Ridge Block 232 in the deepwater U.S. Gulf of Mexico.
	As of December 31, 2014 and 2013, the Company has a net total of $551.3 million and $594.0 million, respectively, of unproved property acquisition costs on the consolidated balance sheets.
	Acquisition costs of unproved properties are assessed for impairment during the holding period and transferred to proved oil and gas properties to the extent associated with successful exploration activities. There are no impairment indicators to date that would require the Company to impair the unproved properties in Blocks 20 and 21 offshore Angola and in the Diaba Block offshore Gabon. For the unproved properties associated with Block 9 offshore Angola, the Company recorded an impairment allowance of $2.5 million on its 40% ownership interest on Block 9 since the Company has no plan to extend its exploration obligations under the Risk Services Agreement for Block 9. Oil and gas leases for unproved properties in the U.S. Gulf of Mexico with a carrying value greater than $1.0 million are assessed individually for impairment based on the Company's current exploration plans and an allowance for impairment is provided if impairment is indicated. Leases that are individually less than $1.0 million in carrying value or are near expiration are amortized on a group basis over the average terms of the leases at rates that provide for full amortization of leases upon lease expiration. These leases have expiration dates ranging from 2015 through 2024. As of December 31, 2014 and 2013, the balance for unproved properties that were subject to amortization before impairment provision was $83.7 million and $68.9 million, respectively. The Company recorded a lease impairment allowance of $70.5 million, $87.0 million and $60.2 million for the years ended December 31, 2014, 2013 and 2012, respectively.
	Capitalized Exploration Well Costs
	If an exploration well provides evidence as to the existence of sufficient quantities of hydrocarbons to justify evaluation for potential development, drilling costs associated with the well are initially capitalized, or suspended, pending a determination as to whether a commercially sufficient quantity of proved reserves can be attributed to the area as a result of drilling. This determination may take longer than one year in certain areas (generally, deepwater and international locations) depending upon, among other things, (i) the amount of hydrocarbons discovered, (ii) the outcome of planned geological and engineering studies, (iii) the need for additional appraisal drilling activities to determine whether the discovery is sufficient to support an economic development plan and (iv) the requirement for government sanctioning in international locations before proceeding with development activities. The following tables reflect the Company's net changes in and the cumulative costs of capitalized exploration well costs (excluding any related leasehold costs):
			December 31,			December 31,			December 31,
			2014			2013			2012
			($ in thousands)
	Beginning of period		$	777,823		$	451,024		$	178,338
	Additions to capitalized exploration
	U.S. Gulf of Mexico:
	Exploration well costs			143,431			154,877			178,295
	Capitalized interest			6,965			3,928			—
	West Africa:
	Exploration well costs			379,461			457,608			168,309
Capitalized interest			44,243			12,271			—
Reclassifications to wells, facilities, and equipment based on determination of proved reserves			—			(38,446	)		—
Amounts charged to expense(1)			(165,459	)		(263,439	)		(73,918	)
End of period		$	1,186,464		$	777,823		$	451,024
-1	The amount of $165.5 million for the year ended December 31, 2014 represents $64.3 million of impairment charges on exploration wells drilled in the U.S. Gulf of Mexico and $101.2 million of impairment charges on exploration wells drilled offshore Angola, all of which did not encounter commercial hydrocarbons. The amount of $263.4 million for the year ended December 31, 2013 represents $120.0 million of impairment charges on exploration wells drilled in the U.S. Gulf of Mexico which did not encounter commercial hydrocarbons, $126.3 million of impairment charges on exploration wells drilled offshore Angola which failed to flow measurable hydrocarbons from drill stem tests and a portion of the cost of exploration wells drilled offshore Angola that were determined to have no utility in the lowest interval beneath the pay zone and $17.1 million of impairment charges on the exploration well drilled offshore Gabon which needed to be re-spud due to mechanical problems with the wellbore.
		December 31,			December 31,
		2014			2013
		($ in thousands)
Cumulative costs:
U.S. Gulf of Mexico
Exploration well costs		$	283,885		$	204,707
Capitalized interest			10,894			3,928
West Africa
Exploration well costs			835,171			556,917
Capitalized interest			56,514			12,271
		$	1,186,464		$	777,823
Well costs capitalized for a period greater than one year after completion of drilling (included in the table above) are summarized as follows:
		Year Ended December 31,
		2014			2013			2012
		($ in thousands)
U.S. Gulf of Mexico		$	208,634		$	186,510		$	89.490
West Africa			566,745			213,265			105,363
		$	775,379		$	399,775		$	194,853
Number of projects with exploration well costs that have been capitalized more than a year			8			3			3
The above capitalized exploration well costs suspended over a year are pending ongoing evaluation including, but not limited to, results of additional appraisal drilling, well-test analysis, additional geological and geophysical data and approval of a development plan. Management believes these discoveries exhibit sufficient indications of hydrocarbons to justify potential development and is actively pursuing efforts to fully assess them. If additional information becomes available that raises substantial doubt as to the economic or operational viability of these discoveries, the associated costs will be expensed at that time.

Other_Assets

Other Assets	12 Months Ended
	Dec. 31, 2014
Other Assets
Other Assets	9. Other Assets
	As of December 31, 2014 and 2013, the balance in other assets consisted of the following:
			December 31,
			2014		2013
			($ in thousands)
	Debt issue cost(1)		$	36,708	$	20,983
	Long-term portion of prepaid shorebase leases			2,244		3,241
	Rig mobilization costs(2)			14,984		11,153
	Long-term accounts receivable(3)			—		17,923
	Other			—		437
			$	53,936	$	53,737
	-1	As of December 31, 2014, the $36.7 million in debt issue costs included $18.5 million and $18.2 million in costs related to the issuance of the Company's 2.625% convertible senior notes due 2019 and the Company's 3.125% convertible senior notes due 2024, respectively, as described in Note 10—Long-term Debt. As of December 31, 2013, the $21.0 million in debt issue costs was related to the issuance of the Company's 2.625% convertible senior notes due 2019 as described in Note 10—Long-term Debt. These debt issue costs are amortized over the life of the notes using the effective interest method.
	-2	As of December 31, 2014 and 2013, the $15.0 million and $11.2 million, respectively, relate to costs associated with the long-term mobilization and the regulatory acceptance testing of the SSV Catarina drilling rig which is currently drilling in West Africa, and costs relating to the Rowan Reliance drilling rig which was delivered in January 2015 and is currently drilling our North Platte #2 appraisal well. These costs are or will be amortized over the term of the drilling rig contracts.
	-3	As of December 31, 2013, the $17.9 million of long-term accounts receivable was related to a 3.75% cost interest disputed by one of our former partners on Block 9 and 21 offshore Angola. On October 30, 2014, the Company collected the entire balance due from the Company's partner on Block 9 and 21.

Longterm_Debt

Long-term Debt	12 Months Ended
	Dec. 31, 2014
Long-term Debt
Long-term Debt	10. Long-term Debt
	As of December 31, 2014, the Company's long-term debt consists of the 2.625% convertible senior notes due 2019 issued on December 17, 2012 (the "2.625% Notes") and the 3.125% convertible senior notes due 2024 issued on May 13, 2014 (the "3.125% Notes", and, collectively with the 2.625% Notes, the "Notes") as follows:
	2.625% Convertible Senior Notes due 2019
	On December 17, 2012, the Company issued $1.38 billion aggregate principal amount of the 2.625% Notes. The 2.625% Notes are the Company's senior unsecured obligations and interest is payable semi-annually in arrears on June 1 and December 1 of each year. The 2.625% Notes will mature on December 1, 2019, unless earlier repurchased or converted in accordance with the terms of the 2.625% Notes. The 2.625% Notes may be converted at the option of the holder at any time prior to 5:00 p.m., New York City time, on the second scheduled trading day immediately preceding the maturity date, in multiples of $1,000 principal amount. The 2.625% Notes are convertible at an initial conversion rate of 28.023 shares of common stock per $1,000 principal amount, representing an initial conversion price of approximately $35.68 per share for a total of approximately 38.7 million underlying shares. The conversion rate is subject to adjustment upon the occurrence of certain events, as defined in the indenture governing the 2.625% Notes, but will not be adjusted for any accrued and unpaid interest except in limited circumstances. Upon conversion, the Company's conversion obligation may be satisfied, at the Company's option, in cash, shares of common stock or a combination of cash and shares of common stock.
	3.125% Convertible Senior Notes due 2024
	On May 13, 2014, the Company issued $1.3 billion aggregate principal amount of the 3.125% Notes. The 3.125% Notes are the Company's senior unsecured obligations and rank equal in right of payment to the 2.625% Notes. Interest on the 3.125% Notes is payable semi-annually in arrears on May 15 and November 15 of each year. The 3.125% Notes will mature on May 15, 2024, unless earlier repurchased, converted or redeemed in accordance with the terms of the Notes. Prior to November 15, 2023, the 3.125% Notes are convertible only under the following circumstances: (1) during any fiscal quarter commencing after September 30, 2014 (and only during such fiscal quarter), if the last reported sale price of the Company's common stock for at least 20 trading days (whether or not consecutive) during a 30 consecutive trading-day period ending on, and including, the last trading day of the immediately preceding fiscal quarter exceeds $30.00 on each applicable trading day; (2) during the five business-day period after any five consecutive trading-day period (the "3.125% Notes Measurement Period") in which the trading price per $1,000 principal amount of notes for each trading day of the 3.125% Notes Measurement Period was less than 98% of the product of the last reported sale price of the Company's common stock and the conversion rate on each such trading day; (3) if the Company calls all or any portion of the 3.125% Notes for redemption, at any time prior to 5:00 p.m., New York City time, on the second scheduled trading day immediately preceding the related redemption date; or (4) upon the occurrence of specified distributions or the occurrence of specified corporate events. On or after November 15, 2023, the 3.125% Notes may be converted at the option of the holder at any time prior to 5:00 p.m., New York City time, on the second scheduled trading day immediately preceding the stated maturity date, in multiples of $1,000 principal amount. As of December 31, 2014 and 2013, none of the conditions allowing holders of the 3.125% Notes to convert had been met.
	The 3.125% Notes are convertible at an initial conversion rate of 43.3604 shares of common stock per $1,000 principal amount, representing an initial conversion price of approximately $23.06 per share for a total of approximately 56.4 million underlying shares. The conversion rate is subject to adjustment upon the occurrence of certain events, as defined in the indenture governing the 3.125% Notes, but will not be adjusted for any accrued and unpaid interest except in limited circumstances. Upon conversion, the Company's conversion obligation may be satisfied, at the Company's option, in cash, shares of common stock or a combination of cash and shares of common stock.
	Holders of the Notes who convert their Notes in connection with a "make- whole fundamental change", as defined in the indenture governing these Notes, may be entitled to a make-whole premium in the form of an increase in the conversion rate. Additionally, in the event of a fundamental change, as defined in the indenture governing the Notes, holders of the Notes may require the Company to repurchase for cash all or a portion of their Notes equal to $1,000 or a multiple of $1,000 at a fundamental change repurchase price equal to 100% of the principal amount of Notes, plus accrued and unpaid interest, if any, to, but not including, the fundamental change repurchase date.
	Upon the occurrence of an Event of Default, as defined within the indenture governing the Notes, the trustee or the holders of at least 25% in aggregate principal amount of the Notes then outstanding may declare 100% of the principal of, and accrued and unpaid interest on, all the Notes to be due and payable immediately.
	In accordance with accounting guidance relating to, "Debt with Conversion and Other Options", the Company separately accounts for the liability and equity conversion components of the Notes due to the Company's option to settle the conversion obligation in cash. The fair value of the Notes excluding the conversion feature at the date of issuance was calculated based on the fair value of similar non-convertible debt instruments. The resulting value of the conversion option of the Notes was recognized as a debt discount and recorded as additional paid-in capital on the Company's consolidated balance sheets. Total debt issue cost on the Notes was allocated to the liability component and to the equity component of the Notes accordingly. The debt discount and the liability component of the debt issue costs are amortized over the term of the Notes. The effective interest rate used to amortize the debt discount and the liability component of the debt issue costs were approximately 8.40% and 8.97% on the 2.625% Notes and the 3.125% Notes, respectively, based on the Company's estimated non-convertible borrowing rate as of the date the Notes were issued. Since the Company incurred losses for all periods, the impact of the conversion option would be anti-dilutive to the earnings per share and therefore was not included in the calculation.
	The carrying amounts of the liability components of the Notes were as follows:
			December 31, 2014								December 31, 2013
			Principal			Unamortized			Carrying		Principal		Unamortized			Carrying
			Amount			discount(1)			Amount		Amount		discount			Amount
			($ in thousands)
	Carrying amount of liability component
	2.625% Notes		$	1,380,000		$	(295,509	)	$	1,084,491	$	1,380,000	$	(344,020	)	$	1,035,980
	3.125% Notes			1,300,000			(455,963	)		844,037		—		—			—
	Total		$	2,680,000		$	(751,472	)	$	1,928,528	$	1,380,000	$	(344,020	)	$	1,035,980
	-1	Unamortized discount will be amortized over the remaining life of the Notes which is 5 years for the 2.625% Notes and 9.50 years for the 3.125% Notes.
	The carrying amounts of the equity components of the Notes were as follows:
			December 31,			December 31,
			2014			2013
			($ in thousands)
	Debt discount relating to value of conversion option		$	866,340		$	390,540
	Debt issue costs			(20,185	)		(9,124	)
	Total		$	846,155		$	381,416
	Fair Value The fair value of the Notes excluding the conversion feature was calculated based on the fair value of similar non-convertible debt instruments since an observable quoted price of the Notes or a similar asset or liability is not readily available. As of December 31 2014 and 2013, the fair values of the Notes were as follows:
			December 31,			December 31,
			2014			2013
			($ in thousands)
	2.625% Notes		$	1,361,000		$	1,227,000
	3.125% Notes			1,047,000			—
	Total		$	2,408,000		$	1,227,000
	As of December 31, 2014, the Company had $8.0 million in accrued interests on the Notes.
	Interest expense associated with the 2.625% convertible senior notes due 2019 and the 3.125% convertible senior notes due 2024 was as follows:
			For Year Ended December 31,
			2014			2013			2012
			($ in thousands)
	Interest expense associated with accrued interest(1)		$	3,271		$	18,529		$	1,294
	Interest expense associated with accretion of debt discount			68,348			44,789			1,843
	Interest expense associated with amortization of debt issue costs			3,149			2,058			75
			$	74,768		$	65,376		$	3,212
	-1	The $3.3 million, $18.5 million and $1.3 million for the years ended December 31, 2014, 2013 and 2012, respectively, represent interest expense net of capitalized amounts of $58.5 million, $17.7 million and $0 million, respectively.
	As of December 31, 2014, and December 31, 2013, the debt discounts associated with our convertible senior notes resulted in the recognition of $264.3 million and $121.0 million of deferred tax liability, respectively. The Company is in an overall net deferred tax assets position with a full valuation allowance. Therefore, the Company has determined that it is more likely than not that all of the deferred tax assets will not be realized.

Contractual_Obligations

Contractual Obligations	12 Months Ended
	Dec. 31, 2014
Contractual Obligations
Contractual Obligations	11. Contractual Obligations
	The short-term and long-term contractual obligations consist of the following:
			December 31,		December 31,
			2014		2013
			($ in thousands)
	Short-term Contractual Obligations:
	Social obligation payments for Block 9, offshore Angola		$	560	$	150
	Social obligation payments for Block 21, offshore Angola			1,156		300
	Social obligation and bonus payments for Block 20, offshore Angola(1)			48,569		48,569
			$	50,285	$	49,019
	Long-term Contractual Obligations:
	Social and work program obligation payments for Block 9, offshore Angola		$	21,875	$	669
	Social obligation payments for Block 21, offshore Angola			74		1,381
	Social obligation and bonus payments for Block 20, offshore Angola(1)			79,996		122,851
			$	101,945	$	124,901
	-1	The total amount of $128.6 million under social obligation payments for Block 20 has been capitalized in unproved oil and gas leasehold. See Note 8—Property, Plants and Equipment.

Stockholders_Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2014
Stockholders' Equity
Stockholders' Equity	12. Stockholders' Equity
	On January 15, 2012, the Company withheld the issuance of an aggregate amount of 9,127 shares of its common stock, at a price of $18.74 per share, to satisfy tax withholding obligations of certain of its officers that arose upon the distribution of deferred stock compensation.
	On February 29, 2012, the Company issued 18,050,000 shares of common stock at a public offering price of $28.00 per share.
	On December 17, 2012, the Company issued $1.38 billion aggregate principal amount of its 2.625% convertible senior notes due 2019. As of December 31, 2013 and 2012, $381.4 million was recorded as the equity component of the 2.625% Notes. See also Note 10—Long-term Debt.
	On May 13, 2014, the Company issued $1.3 billion aggregate principal amount of its 3.125% convertible senior notes due on 2024. As of December 31, 2014, $464.7 million was recorded as the equity component of the 3.125% Notes. See also Note 10—Long-term Debt.

Seismic_and_Exploration_Expens

Seismic and Exploration Expenses	12 Months Ended
	Dec. 31, 2014
Seismic and Exploration Expenses
Seismic and Exploration Expenses	13. Seismic and Exploration Expenses
	Seismic and exploration expenses consisted of the following:
		For Year Ended December 31,
		2014		2013		2012
		($ in thousands)
	Seismic costs	$	34,359	$	63,721	$	42,447
	Leasehold delay rentals		7,391		6,660		6,383
	Drilling rig expense and other exploration expense		43,817		3,832		12,753
		$	85,567	$	74,213	$	61,583

Equity_Based_Compensation

Equity Based Compensation	12 Months Ended
	Dec. 31, 2014
Equity Based Compensation
Equity Based Compensation	14. Equity based Compensation
	Overview.    Under the Company's Long Term Incentive Plan (the "Incentive Plan"), the Company may issue stock options, stock appreciation rights, restricted stock, restricted stock units, performance awards and other stock-based awards to employees. At December 31, 2014, 4,043,263 shares remain available for grant under the Incentive Plan. However, on January 15, 2015 the Company granted a total of 379,746 shares of restricted stock and 746,268 stock options to three senior officers as required pursuant to their employment agreements. In addition, on February 19, 2015, the Company awarded 2,757,982 shares of restricted stock and 1,526,835 stock appreciation rights to employees as part of the Company's annual long-term equity incentive program. These awards combined with first quarter new hire and termination activity representing a net new issuance of 26,853 shares has resulted in 132,414 shares remaining available for issuance under the Incentive Plan as of February 19, 2015.
	On January 28, 2010, the Company adopted the Non-Employee Directors Compensation Plan (the "NED Plan"). Under the NED Plan, the Company may issue options, restricted stock units, other stock-based award or retainers to non-employee directors. At December 31, 2014, 415,682 shares remain available for grant under the NED Plan.
	In accordance with ASC No. 718, Compensation—Stock Compensation, the Company recognizes compensation cost for equity-based compensation to employees and non-employee directors over the period during which the recipient is required to provide service in exchange for the award, based on the fair value of the equity instrument on the date of grant, net of estimated forfeitures. If actual forfeitures differ from the Company's estimates, additional adjustments to compensation expense will be required in future periods.
	Restricted Stock.    The Company accounted for the restricted stock based on ASC Topic 718 as described above. For restricted stock awards with market conditions, the fair value of the awards is measured using the asset-or-nothing option pricing model. Restricted stock awards without market conditions and the performance-based awards are valued using the market price of the Company's common stock on the grant date. The Company records compensation cost, net of estimated forfeitures, for stock-based compensation awards over the requisite service period except for performance-based awards. For performance-based awards, compensation cost is recognized over the requisite service period as and when the Company determines that the achievement of the performance condition is probable, using the per-share fair value measured at grant date.
	The following table summarizes the information about the restricted stock awarded to employees for years ended December 31, 2014, 2013 and 2012:
			Year Ended December 31,
			2014					2013					2012
			Restricted			Weighted		Restricted			Weighted		Restricted			Weighted
			Shares			Average		Shares			Average		Shares			Average
						Grant Date					Grant Date					Grant Date
						Fair Value					Fair Value					Fair Value
						Per Share					Per Share					Per Share
	Non-vested shares at beginning of year			4,334,886		$	14.31		4,040,825		$	13.05		4,599,783		$	11.27
	Granted			2,275,317		$	14.53		620,840		$	24.58		487,710		$	26.01
	Vested			(1,433,172	)	$	16.32		(239,317	)	$	17.37		(738,628	)	$	13.05
	Forfeited or expired(1)			(2,374,242	)	$	10.63		(87,462	)	$	20.91		(308,040	)	$	12.17
	Non-vested shares at end of year			2,802,789		$	16.44		4,334,886		$	14.31		4,040,825		$	13.05
	Weighted-average vesting period remaining			3.08 years					1.22 years					1.87 years
	Unrecognized compensation ($ in thousands)		$	34,066				$	22,467				$	23,827
	-1	The 2,374,242 forfeited or expired restricted shares for the year ended December 31, 2014 include 2,306,173 restricted shares that were forfeited on December 21, 2014 because the market condition attached to the vesting terms of the awards was not met.
	A total of 58,038 restricted stock units were granted to non-employee directors during the year ended December 31, 2014. As of December 31, 2014, the Company has granted a cumulative total of 235,801 restricted stock units to non-employee directors. For the years ended December 31, 2014, 2013 and 2012, the Company also granted 26,438, 15,318 and 12,221 shares of common stock, respectively, for annual retainers to non-employee directors who elected to be compensated by stock in lieu of cash payments. For the years ended December 31, 2014, 2013 and 2012, the weighted average fair values of these shares at grant date were $17.52, $25.40 and $21.35 per share, respectively.
	Non-Qualified Stock Options.    The Company grants non-qualified stock options to employees at an exercise price equal to the market value of the Company's common stock on the grant date. The non-qualified stock option awards have contractual terms of 10 years. The options granted in February 2014 and 2013 will vest 50% at the end of the third year from date of grant and 50% at the end of the fourth year from date of grant. The options granted in 2012 were fully vested during the year ended December 31, 2014.
	The fair value of each stock option granted is determined using the Black-Scholes-Merton option-pricing model based on several assumptions. These assumptions are based on management's best estimate at the time of grant. The Company used the following the weighted average of each assumption based on the grants in 2014:
			2014
	Expected Term in Years			5.5
	Expected Volatility			57.27	%
	Expected Dividends			—	%
	Risk-Free Interest Rate			1.69	%
	The Company estimates expected volatility based on an analysis of its stock price since the IPO and comparing the stock price volatility for the period from IPO date through December 31, 2014 with the historical stock price volatility of a similar exploration and production company. The Company estimates the expected term of its option awards based on the vesting period and average remaining contractual term, referred to as the "simplified method". The Company uses this method to provide a reasonable basis for estimating its expected term based on a lack of sufficient historical employee exercise data on stock option awards.
	A summary of the stock options activities for the year ended December 31, 2014 is presented below:
			Shares			Weighted		Weighted-Average			Aggregate
						Average		Remaining			Intrinsic Value
						Exercise		Contractual Term			(thousands)
						Price		(years)
	Outstanding at January 1, 2014			2,338,718		$	20.24		8		$	—
	Granted			812,055		$	17.5
	Exercised			(3,005	)	$	12.45				$	17,837
	Forfeited or expired			(11,221	)	$	24.02
	Outstanding at December 31, 2014			3,136,547		$	19.52		7.57		$	—
	Vested or expected to vest at December 31, 2014			1,693,193		$	20.82		8.61		$	—
	Exercisable at December 31, 2014			1,411,271		$	17.93		6.3		$	—
	The weighted-average grant-date fair value of stock options granted during 2014 and 2013 was $9.12 and $14.08 per option, respectively, using the Black-Scholes option-pricing model. As of December 31, 2014, $12.2 million of total unrecognized compensation cost related to stock options is expected to be recognized over a weighted-average period of 2.46 years.
	Restricted Stock Units.    On December 3, 2010, the Company granted 198,838 restricted stock units to employees pursuant to a Restricted Stock Unit (RSU) Award Agreement. Under the RSU Award Agreement the share-based payment was earned based on the number of successful wells drilled during the three year period ending December 31, 2013. The RSU award vested within a range of 0% to 200% of the number of RSU shares awarded on scheduled vesting dates contingent upon the recipient's continued service at each vesting date and based on the achievement of successful wells drilled as defined in the RSU Award Agreement. The recipients could not vest in an amount greater than 200% of the Award or in aggregate 397,676 RSU shares. The percentage of the RSU awards vested at each of the three year periods ending December 31, 2013 was calculated by the number of successful wells drilled during the respective years multiplied by vesting percentages ranging from 25% to 37.5%. As of December 31, 2014, the RSU shares were fully vested.
	A summary of the restricted stock units activities for the years ended December 31, 2014, 2013 and 2012 is presented below:
			Year Ended December 31,
			2014					2013					2012
			Number of			Weighted		Number of			Weighted		Number of			Weighted
			shares			Average		shares			Average		shares			Average
			relating			Grant Date		relating			Grant Date		relating			Grant Date
			Restricted			Fair Value		Restricted			Fair Value		Restricted			Fair Value
			Stock Units			Per Unit		Stock Units			Per Unit		Stock Units			Per Unit
	Non-vested at beginning of year			21,624		$	30.5		109,275		$	30.5		198,838		$	12.45
	Granted			—			—		—			—		—			—
	Vested			(21,624	)	$	30.5		(87,401	)	$	30.5		(74,537	)	$	30.5
	Forfeited or expired			—			—		(250	)	$	30.5		(15,026	)	$	30.5
	Non-vested at end of year			—			—		21,624		$	30.5		109,275		$	30.5
	Weighted-average period remaining			—					—					1 year
	The table below summarizes the equity-based compensation costs recognized for years ended December 31, 2014, 2013 and 2012:
			Year Ended December 31,
			2014			2013		2012
			($ in thousands)
	Restricted stock:
	Employees		$	20,971		$	15,470	$	13,378
Non-employee directors			1,476			1,260		970
Stock options:
Employees			9,295			7,405		3,790
Restricted stock units (performance-based)			—			4,619		4,272
		$	31,742		$	28,754	$	22,410

Employee_Benefit_Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2014
Employee Benefit Plan
Employee Benefit Plan	15. Employee Benefit Plan
	In 2006, the Company established the Cobalt International Energy, L.P., defined contribution 401(k) plan (the Plan). All employees of the Company after three months of continuous employment are eligible to participate in the Plan. The plan is discretionary and provides a 6% employee contribution match as determined by the Company's Board of Directors. Effective December 31, 2009, the Plan was amended to discontinue the employer's matching contributions. Effective January 1, 2012, the Company reinstituted the 6% employee contribution match. For the years ended December 31, 2014, 2013 and 2012, the Company recorded $1.0 million, $0.8 million, and $0.5 million, respectively, in benefits contributions to the Plan, which are included in general and administrative expenses.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2013
Income Taxes
Income Taxes	16. Income Taxes
	For the years ended December 31, 2014, 2013 and 2012, the Company recorded a net deferred tax asset of $568.0 million, $461.6 million, and $269.6 million, respectively with a corresponding full valuation allowance of $568.0 million, $461.6 million, and $269.6 million, respectively, for the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes.
	The components of the income tax provision (benefit) are as follows:
			Year Ended
			December 31,
			2014			2013			2012
			($ in thousands)
	Current taxes:
	U.S. federal		$	—		$	—		$	—
	Foreign			—			—			—
	Deferred taxes:
	U.S. federal			—			—			—
	Foreign			—			—			—
	Total		$	—		$	—		$	—
	The reconciliation of income taxes computed at the U.S. federal statutory tax rate to the Company's income tax expense (benefit) for years ended December 31, 2014, 2013 and 2012 are as follows:
			Year Ended December 31,
			2014			2013			2012
			($ in thousands)
	U.S.:
	Net income (loss) as reported		$	(307,025	)	$	(387,210	)	$	(229,372	)
	Less: net income (loss) applicable to period before corporate reorganization			—			—			—
	Foreign:
	Net income (loss) as reported			(203,738	)		(201,814	)		(53,627	)
	Less: net income (loss) applicable to period before corporate reorganization			—			—			—
	Net income (loss) applicable to period after corporate reorganization		$	(510,763	)	$	(589,024	)	$	(282,999	)
			Year Ended December 31,
			2014						2013					2012
			($ in thousands)
	Income tax expense (benefit) at the federal statutory rate		$	(178,767	)		35	%	$	(206,159	)	35	%	$	(99,050	)	35	%
	State income taxes, net of federal income tax benefit			(828	)		0.2	%		(489	)	0.1	%		(512	)	0.2	%
	Foreign income tax			(111,151	)		21.8	%		(70,994	)	12.1	%		4,447		–1.6	%
	Other			9,098			–1.8	%		366		–0.1	%		2,678		–0.9	%
	Valuation allowance(1)			281,648			–55.2	%		277,276		–47.1	%		92,437		–32.7	%
			$	—			—	%	$	—		—	%	$	—		—	%
	-1	The change in the deferred tax asset valuation allowance of $277.3 million for the year end December 31, 2013, excludes a $85.3 million net decrease in valuation allowance due to previously unrecorded foreign deferred tax assets and a deferred tax liability related to the Company's convertible debt instrument that did not impact the rate reconciliation.
	Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. The significant components of the Company's deferred tax assets and liabilities were as follows:
			As of December 31,
			2014			2013
			($ in thousands)
	Short-term deferred tax liabilities:
	2.625% convertible senior notes due 2019(1)		$	18,479		$	17,061
	3.125% convertible senior notes due 2024(1)			11,855			—
	Total short-term deferred tax liabilities			30,334			17,061
	Long-term deferred tax liabilities:
	2.625% convertible senior notes due 2019		$	85,471		$	103,951
	3.125% convertible senior notes due 2024			148,507			—
	Oil and gas properties			54,461			22,135
	Total long-term deferred tax liabilities			288,439			126,086
	Long-term deferred tax assets:
	Seismic and exploration costs			457,854			280,095
	Stock based compensation			18,092			20,842
	Domestic NOL carry forwards			415,608			273,163
	Foreign NOL carry forwards			38,200			28,633
	Other			(43,021	)		1,976
	Valuation allowance			(567,960	)		(461,562	)
	Total long-term deferred assets			318,773			143,147
	Net long-term deferred assets			30,334			17,061
	Net deferred tax assets		$	—		$	—
	-1	The recognition of the liability and equity components of the debt resulted in a taxable temporary basis difference and recorded as an adjustment to additional paid-in capital.
	The Company has established a full valuation allowance against the deferred tax assets where the Company has determined that it is more likely than not that all of the deferred tax assets will not be realized. Because of the full valuation allowance, no income tax expense or benefit is reflected on the consolidated statement of operations for years ended December 31, 2014, 2013 and 2012.
	The NOL carryforward for federal and state income tax purposes of approximately $1.2 billion and $65.2 million as of December 31, 2014 begins to expire in 2025 and 2024, respectively. The utilization of the NOL carryforwards is dependent upon generating sufficient future taxable income in the appropriate jurisdictions within the carryforward period.
	As of December 31, 2014, the Company had NOL carryforward for foreign income tax purposes of approximately $73.8 million which begins to expire in 2014. The Company has determined that it is more likely than not, that the foreign NOLs will not be fully realized. Therefore, a full valuation allowance was established for these net deferred tax assets.
	There were no unrecognized tax benefits or accrued interest or penalties associated with unrecognized tax benefits as of December 31, 2014 and 2013.

Commitments

Commitments	12 Months Ended
	Dec. 31, 2014
Commitments
Commitments	17. Commitments
	The following table summarizes by period the payments due for the Company's estimated commitments, excluding long-term debt, as of December 31, 2014:
			Payments Due By Year
			2015		2016		2017		2018		2019		Thereafter
			($ in thousands)
	Drilling Rig and Related Contracts		$	544,559	$	299,702	$	208,104	$	17,104	$	—	$	—
	Operating Leases			9,755		4,801		2,309		2,369		2,405		5,626
	Lease Rentals(1)			7,353		5,460		5,007		2,282		1,973		7,223
	Social and Work Program Payment Obligations(2)			55,999		84,729		5,714		5,714		—		—
	Total		$	617,666	$	394,692	$	221,134	$	27,469	$	4,378	$	12,849
	-1	Relates to the annual delay rental payments payable to the Office of Natural Resources Revenue within the U.S. Department of the Interior with respect to the Company's U.S. Gulf of Mexico leases. These annual payments are required to maintain the leases from year to year.
	-2	Includes the Company's contractual payment obligations for (i) social projects such as the Sonangol Research and Technology Center and academic scholarships for Angolan students that the Company was and is contractually obligated to pay in consideration for the Angolan government granting it the licenses to explore for and develop hydrocarbons offshore Angola and (ii) the Company's remaining work program obligations on Block 9 offshore Angola. Pursuant to the terms of the Risk Services Agreements for Blocks 9 and 21 and the Production Sharing Agreement for Block 20, the Company is not required to pay annual rental payments to maintain the licenses from year to year.
	The Company recorded $12.8 million, $6.7 million, and $12.1 million of office and delay rental expense for the years ended December 31, 2014, 2013 and 2012, respectively.

Segment_Information

Segment Information	12 Months Ended
	Dec. 31, 2014
Segment Information
Segment Information	18. Segment Information
	The Company currently has two geographic operating segments for its operations. The operating segments are focused in the deepwater U.S. Gulf of Mexico and offshore West Africa. The following tables provide the geographic operating segment information for years ended December 31, 2014, 2013 and 2012:
			United States			West Africa			Total
			($ in thousands)
	Year ended December 31, 2014
	Operating costs and expense		$	238,214		$	203,727		$	441,941
	Operating income (loss)			(238,214	)		(203,727	)		(441,941	)
	Other income (expense)									(68,822	)
	Net income (loss)								$	(510,763	)
	Additions to Property and Equipment, net(1)		$	135,449		$	320,637		$	456,086
	Year ended December 31, 2013
	Operating costs and expense		$	329,832		$	202,852		$	532,684
	Operating income (loss)			(329,832	)		(202,852	)		(532,684	)
	Other income (expense)									(56,340	)
	Net income (loss)								$	(589,024	)
	Additions to Property and Equipment, net(1)		$	44,124		$	332,395		$	376,519
	Year ended December 31, 2012
	Operating costs and expense		$	231,196		$	53,632		$	284,828
	Operating income (loss)			(231,196	)		(53,632	)		(284,828	)
	Other income (expense)									1,829
	Net income (loss)								$	(282,999	)
	Additions to Property and Equipment, net(1)		$	67,068		$	169,362		$	236,430
	-1	These amounts are net of accumulated allowance for impairment on oil and gas properties and accumulated depreciation and amortization on other property and equipment.

Contingencies

Contingencies	12 Months Ended
	Dec. 31, 2014
Contingencies
Contingencies	19. Contingencies
	The Company is currently, and from time to time may be, subject to various lawsuits, claims and proceedings that arise in the normal course of business, including employment, commercial, environmental, safety and health matters. It is not presently possible to determine whether any such matters will have a material adverse effect on the Company’s consolidated financial position, results of operations, or liquidity.

Other_Matters

Other Matters	12 Months Ended
	Dec. 31, 2014
Other Matters
Other Matters	20. Other Matters
	As previously disclosed, in November 2011 a formal order of investigation was issued by the SEC related to our operations in Angola. In August 2014, we received a Wells Notice from the SEC related to this investigation. In January 2015, we received a termination letter from the SEC advising us that the SEC's FCPA investigation has concluded and the Staff does not intend to recommend any enforcement action by the SEC. This letter formally concluded the SEC's investigation. We continue to cooperate with the Department of Justice ("DOJ") with regard to its ongoing parallel investigation. We are unable to predict the outcome of the DOJ's ongoing investigation or any action that the DOJ may decide to pursue.

Related_Party_Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2014
Related Party Transactions
Related Party Transactions	21. Related Party Transactions
	On February 20, 2013, the Company entered into software licensing and consulting service agreements with Quorum Business Solutions, Inc. ("Quorum") and Quorum Business Solutions (U.S.A.), Inc, related to certain enterprise resource planning software. Under these agreements, Quorum will license, host, and support this software for us for an initial term of three years. The approximate value of these agreements is $1.5 million. Quorum is owned in part by Riverstone Holdings, LLC, one of our former financial sponsors. For the years ended December 31, 2014 and 2013, the Company incurred a total of 1.5 million and $1.3 million, respectively, in costs relating to Quorum. The Company did not have any material related party transactions for the year ended December 31, 2012.

Selected_Quarterly_Financial_D

Selected Quarterly Financial Data-Unaudited	12 Months Ended
	Dec. 31, 2014
Selected Quarterly Financial Data-Unaudited
Selected Quarterly Financial Data-Unaudited	22. Selected Quarterly Financial Data—Unaudited
	Unaudited quarterly financial data for the years ended December 31, 2014 and 2013 are as follows:
			1st Quarter			2nd Quarter			3rd Quarter			4th Quarter
			($ in thousands, except per share data)
	Year ended December 31, 2014
	Operating costs and expenses		$	47,293		$	77,591		$	120,961		$	196,097
	Operating income (loss)			(47,293	)		(77,591	)		(120,961	)		(196,097	)
	Net income (loss)			(56,915	)		(94,756	)		(142,529	)		(216,564	)
	Basic and diluted income (loss) per common share(1)		$	(0.14	)	$	(0.23	)	$	(0.35	)	$	(0.53	)
	Year ended December 31, 2013
	Operating costs and expenses		$	112,452		$	65,365		$	145,663		$	209,204
	Operating income (loss)			(112,452	)		(65,365	)		(145,663	)		(209,204	)
	Net income (loss)			(128,087	)		(78,818	)		(160,000	)		(222,119	)
	Basic and diluted income (loss) per common share(1)		$	(0.31	)	$	(0.19	)	$	(0.39	)	$	(0.55	)
	-1	Totals may not add due to rounding.

Supplemental_Information_on_Oi

Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited)	12 Months Ended
	Dec. 31, 2014
Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited)
Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited)	23. Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited)
	The unaudited supplemental information on oil and gas exploration activities that follows is presented in accordance with supplemental disclosure requirements under ASC No. 932, "Extractive Activities—Oil and Gas" ("ASC No. 932") and the Securities and Exchange Commission's final rule, Modernization of Oil and Gas Reporting. Disclosures include (1) capitalized costs, costs incurred and results of operations related to oil and gas producing activities, (2) net proved oil and gas reserves, and (3) a standardized measure of discounted future net cash flows relating to proved oil and gas reserves. Since the Company did not have any production activities for years ended December 31, 2014, 2013 and 2012, there will be no disclosures on results of operations related to oil and gas producing activities.
	Capitalized Costs Related to Oil and Gas Activities
			U.S. Gulf			West Africa			Total
			of Mexico
			($ in thousands)
	As of December 31, 2014
	Unproved properties(1)		$	699,426		$	1,249,556		$	1,948,982
	Accumulated valuation allowance			(208,724	)		(2,500	)		(211,224	)
				490,702			1,247,056			1,737,758
	Proved properties			183,221			—			183,221
	Net capitalized costs		$	673,923		$	1,247,056		$	1,920,979
	As of December 31, 2013
	Unproved properties		$	605,658		$	927,059		$	1,532,717
	Accumulated valuation allowance			(160,913	)		—			(160,913	)
				444,745			927,059			1,371,804
	Proved properties			92,579			—			92,579
	Net capitalized costs		$	537,324		$	927,059		$	1,464,383
	-1	Unproved properties include capitalized costs net of sale/like-kind exchange of leasehold interest transactions that occurred in 2014 and 2013 of approximately $5.6 million and $10.7 million, respectively, for the U.S. Gulf of Mexico. No gain or loss was recognized for these transactions for the years ended December 31, 2014 and 2013.
	Costs Incurred in Oil and Gas Activities
	The following table reflects total costs incurred, both capitalized and expensed, for oil and gas property acquisition, exploration and development activities:
			U.S. Gulf			West Africa			Total
			of Mexico
			($ in thousands)
	Year ended December 31, 2014
	Property acquisition
	Unproved		$	27,784		$	—		$	27,784
	Proved			—			—			—
	Exploration
	Capitalized			150,396			423,704			574,100
	Expensed			31,531			54,036			85,567
	Development			90,642			—			90,642
	Total Costs Incurred		$	300,353		$	477,740		$	778,093
	Year ended December 31, 2013
	Property acquisition
	Unproved		$	37,584		$	—		$	37,584
	Proved			—			—			—
	Exploration
	Capitalized			158,806			469,879			628,685
	Expensed			48,688			25,525			74,213
	Development			54,133			—			54,133
	Total Costs Incurred		$	299,211		$	495,404		$	794,615
	Year ended December 31, 2012
	Property acquisition
	Unproved		$	19,961		$	—		$	19,961
	Proved			—			—			—
	Exploration
	Capitalized			178,295			168,309			346,604
	Expensed			32,874			28,709			61,583
	Development			—			—			—
	Total Costs Incurred		$	231,130		$	197,018		$	428,148
	All of the Company's proved reserves are located in the U.S. Gulf of Mexico. Reserve quantity information for the years ended December 31, 2014, 2013 and 2012 are as follows:
			Natural Gas			Oil and			Equivalent
			(in Bcf)			Condensate			Volumes
						(in MMBbls)			(in MMBOE)
	Proved undeveloped reserves:
	Balance at December 31, 2012			—			—			—
	Discoveries			3.4			7.9			8.5
	Balance at December 31, 2013			3.4			7.9			8.5
	Revisions			0.3			0.5			0.5
	Balance at December 31, 2014			3.7			8.4			9.0
	The reserves as of December 31, 2014 presented above were prepared by the independent engineering firm, Netherland, Sewell & Associates, Inc. ("NSAI"). These reserves are located in the U.S. Gulf of Mexico. Proved oil and natural gas reserves are the estimated quantities of oil and natural gas which geological and engineering data demonstrate, with reasonable certainty, to be recoverable in future years from known reservoirs under economic and operating conditions (i.e., prices and costs) existing at the time the estimate is made. Proved developed oil and natural gas reserves are proved reserves that can be expected to be recovered through existing wells and equipment in place and under operating methods being utilized at the time the estimates were made. A variety of methodologies are used to determine the Company's proved reserve estimates. The principal methodologies employed are decline curve analysis, advance production type curve matching, petrophysics/log analysis and analogy. Some combination of these methods is used to determine reserve estimates in substantially all of the Company's fields. The Company emphasizes that reserve estimates are inherently imprecise and that estimates of new discoveries and undeveloped locations are more imprecise than estimates of established proved producing oil and gas properties. Accordingly, these estimates are expected to change as future information becomes available.
	Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves
	The Company follows the guidelines prescribed in ASC No. 932 for computing a standardized measure of future net cash flows and changes therein relating to estimated proved reserves. The following summarizes the policies used in the preparation of the accompanying oil and natural gas reserve disclosures, standardized measures of discounted future net cash flows from proved oil and natural gas reserves and the reconciliations of standardized measures from year to year.
The information is based on estimates of proved reserves attributable to the Company's interest in oil and natural gas properties as of December 31, 2014 and 2013. The Company did not have proved reserves as of December 31, 2012. These estimates were prepared by NSAI.
The standardized measure of discounted future net cash flows from production of proved reserves was developed as follows:
-1	Estimates are made of quantities of proved reserves and future periods during which they are expected to be produced based on year-end economic conditions.
-2	The estimated future cash flows are compiled by applying the twelve month average of the first of the month prices of crude oil and natural gas relating to the Company's proved reserves to the year-end quantities of those reserves for reserves.
-3	The future cash flows are reduced by estimated production costs, costs to develop and produce the proved reserves and abandonment costs, all based on year-end economic conditions, plus Company overhead incurred.
-4	Future income tax expenses are based on year-end statutory tax rates giving effect to the remaining tax basis in the oil and natural gas properties, other deductions, credits and allowances relating to the Company's proved oil and natural gas reserves.
-5	Future net cash flows are discounted to present value by applying a discount rate of 10%.
The assumptions used to compute the standardized measure are those prescribed by the U.S. Generally Accepted Accounting Principles. These assumptions do not necessarily reflect the Company's expectations of actual revenues to be derived from those reserves, nor their present value. The limitations inherent in the reserve quantity estimation process, as discussed previously, are equally applicable to the standardized measure computations, since these reserve quantity estimates are the basis for the valuation process. The Company emphasizes that reserve estimates are inherently imprecise and that estimates of new discoveries and undeveloped locations are more imprecise than estimates of established proved producing oil and gas properties. The standardized measure of discounted future net cash flows does not purport, nor should it be interpreted, to present the fair value of the Company's oil and natural gas reserves. An estimate of fair value would also take into account, among other things, the recovery of reserves not presently classified as proved, anticipated future changes in prices and costs and a discount factor more representative of the time value of money and the risks inherent in reserve estimates.
Prices used in the report prepared by NSAI are based on the 12-month unweighted arithmetic average of the first-day-of-the-month price for each month in the period January through December 2014. For oil volumes, the average Light Louisiana Sweet spot price of $98.48 per barrel is adjusted for quality, transportation fees, and a regional price differential. For gas volumes, the average Henry Hub spot price of $4.350 per MMbtu is adjusted for energy content, transportation fees, and a regional price differential. All prices are held constant throughout the lives of the properties. For the proved reserves, the average adjusted product prices weighted by production over the remaining lives of the properties are $95.24 per barrel of oil and $4.770 per Mcf of gas.
Information with respect to the Company's estimated discounted future net cash flows related to its proved oil and natural gas reserves as of December 31, 2014 and 2013 are as follows:
		2014			2013
		($ in thousands)
Future cash inflows		$	814,394		$	830,287
Future production costs			(12,710	)		(6,400	)
Future development costs			(244,306	)		(302,278	)
Future income tax expense(1)			—			—
Future net cash flows			557,378			521,609
10% annual discount for estimated timing of cash flows			(192,094	)		(244,976	)
Standardized measure of discounted future net cash flows		$	365,284		$	276,633
-1	There is no future income tax expense as of December 31, 2014, as the tax basis of the oil and gas properties in the United States and net operating losses attributable to oil and gas operations exceed the future net revenues.
Information with respect to the Company's standardized measure of discounted future net cash flows as of December 31, 2014 and 2013 are as follows:
		2014			2013
		($ in thousands)
Standardized measure, beginning		$	276,633		$	—
Discoveries			—			276,633
Revisions of previous estimates:			—			—
Changes in prices and costs			(36,869	)		—
Changes in future development costs			49,700			—
Changes in quantities			17,351			—
Accretion of discount			27,663			—
Changes in timing and other			30,806			—
Standardized measure, ending		$	365,284		$	276,633

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation
	At December 31, 2014, the accompanying consolidated financial statements include the accounts of the Company and the Partnership. Prior to the effective date of a corporate reorganization, both entities were under common control arising from common direct or indirect ownership of each. The transfer of the Partnership interests to the Company represented a reorganization of entities under common control and was accounted for at historical cost.
Recently Issued Accounting Standards	Recently Issued Accounting Standards
	In June 2014, the Financial Accounting Standards Board (the "FASB") amended Accounting Standard Codification Topic No. 915, Development Stage Entities (the "ASC Topic 915"), to remove the definition of a development stage entity from the Master Glossary of the ASC, thereby removing the financial reporting distinction between development stage entities and other reporting entities. The amendments eliminate the requirements for development stage entities to (1) present inception-to-date information in the statements of income, cash flows, and shareholder equity, (2) label the financial statements as those of a development stage entity, (3) disclose a description of the development stage activities in which the entity is engaged, and (4) disclose in the first year in which the entity is no longer a development stage entity that in prior years it had been in the development stage.
	These amendments and the other remaining disclosure requirements of the ASC Topic 915 should be applied retrospectively. For public business entities, ASC Topic 915 is effective for annual reporting periods beginning after December 15, 2014, and interim periods therein. Early application of ASC Topic 915 is permitted for any annual reporting period or interim period for which the entity's financial statements have not yet been issued or made for issuance. Upon adoption, entities will no longer present or disclose any information required by the ASC Topic 915. The Company elected to apply ASC Topic 915 early effective in the Form 10-Q for the quarter ended June 30, 2014 and other reports thereafter.
Use of Estimates	Use of Estimates
	The preparation of financial statements in conformity with United States generally accepted accounting principles ("GAAP") requires the Company to make estimates and assumptions that affect the reported amounts of assets including proved reserves and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Significant estimates the Company makes include (a) accruals related to expenses, (b) assumptions used in estimating fair value of equity based awards and the fair value of the liability component of the convertible senior notes and (c) assumptions used in impairment testing. Although the Company believes these estimates are reasonable, actual results could differ from these estimates.
Fair Value Measurements	Fair Value Measurements
	The fair values of the Company's cash and cash equivalents, joint interest and other receivables, restricted funds and investments approximate their carrying amounts due to their short-term duration. The hierarchy below lists three levels of fair value based on the extent to which inputs used in measuring fair value are observable in the market. The Company categorizes each of its fair value measurements as applicable to one of these three levels based on the lowest level input that is significant to the fair value measurement in its entirety. The levels are:
	Level 1—Quoted prices in active markets that are accessible at the measurement date for identical assets or liabilities. This category includes the Company's cash and money market funds.
	Level 2—Quoted prices in non-active markets or in active markets for similar assets or liabilities, and inputs other than quoted prices that are observable, for the asset or liability, either directly or indirectly for substantially the full contractual term of the asset or liability being measured. This category includes the Company's U.S. Treasury bills, U.S. Treasury notes, U.S. Government agency securities, commercial paper, corporate bonds and certificates of deposits.
	Level 3—Inputs that are generally unobservable and typically reflect management's estimate of assumptions that market participants would use in pricing the asset or liability. The Company does not currently have any financial instruments categorized as Level 3.
Revenue Recognition	Revenue Recognition
	The Company will follow the "sales" (or cash) method of accounting for oil and gas revenues. Under this method, the Company will recognize revenues on the volumes sold. The volumes sold may be more or less than the volumes to which the Company is entitled based on its ownership interest in the property. These differences result in a condition known in the industry as a production imbalance. For the years ended December 31, 2014, 2013 and 2012, no revenues have been recognized in these consolidated financial statements.
Cash and Cash Equivalents	Cash and Cash Equivalents
	Cash and cash equivalents consist of demand deposits and funds invested in highly liquid instruments with maturities of three months or less from the date of purchase. Demand deposits typically exceed federally insured limits; however, the Company periodically assesses the financial condition of the institutions where these funds are held as well as the credit ratings of the issuers of the highly liquid instruments and believes that the credit risk is minimal.
Restricted Funds	Restricted Funds
	Restricted funds consist of collateral for letters of credit relating to our operations offshore Angola.
Investments	Investments
	The Company's policy on accounting for its investments, which consist entirely of debt securities, is based on the accounting guidance relating to "Accounting for Certain Investments in Debt and Equity Securities." The Company considers all highly liquid interest-earning investments with a maturity of three months or less at the date of purchase to be cash equivalents. Investments with original maturities of greater than three months and remaining maturities of less than one year are classified as short-term investments. Investments with maturities beyond one year are classified as long-term investments. The debt securities are carried at amortized costs and classified as held-to-maturity securities as the Company has the positive intent and ability to hold them until they mature. The net carrying value of held-to-maturity securities is adjusted for amortization of premiums and accretion of discounts to maturity over the life of the securities. Held-to-maturity securities are stated at amortized cost, which approximates fair market value as of December 31, 2014 and 2013. Income related to these securities is reported as a component of interest income in the Company's consolidated statement of operations. See Note 6—Investments.
	Investments are considered to be impaired when a decline in fair value is determined to be other-than-temporary. The Company conducts a regular assessment of its debt securities with unrealized losses to determine whether securities have other-than-temporary impairment ("OTTI"). This assessment considers, among other factors, the nature of the securities, credit rating or financial condition of the issuer, the extent and duration of the unrealized loss, market conditions and whether the Company intends to sell or whether it is more likely than not that the Company will be required to sell the debt securities. As of December 31, 2014 and 2013, the Company has no OTTI in its debt securities.
Capitalized Interest	Capitalized Interest
	For exploration and development projects that have not commenced production, interest is capitalized as part of the historical cost of developing and constructing assets. Capitalized interest is determined by multiplying the Company's weighted-average borrowing cost on debt by the average amount of qualifying costs incurred. Once an asset subject to interest capitalization is completed and placed in service, the associated capitalized interest is expensed through depreciation or impairment. See Note 8—Property, Plant, and Equipment and Note 10—Long-term Debt.
Joint Interest and Other Receivables	Joint Interest and Other Receivables
	Joint interest and other receivables result primarily from billing shared costs under the respective operating agreements to the Company's partners. These receivables are usually settled within 30 days of the invoice date.
Property, Plant, and Equipment	Property, Plant, and Equipment
	The Company uses the "successful efforts" method of accounting for its oil and gas properties. Acquisition costs for unproved leasehold properties and costs of drilling exploration wells are capitalized pending determination of whether proved reserves can be attributed to the areas as a result of drilling those wells. Under the successful efforts method of accounting, proved leasehold costs are capitalized and amortized over the proved developed and undeveloped reserves on a units-of-production basis. Successful drilling costs, costs of development and developmental dry holes are capitalized and amortized over the proved developed reserves on a units-of-production basis. Significant unproved leasehold costs are capitalized and are not amortized, pending an evaluation of their exploration potential. Unproved leasehold costs are assessed periodically to determine if an impairment of the cost of individual properties has occurred. Factors taken into account for impairment analysis include results of the technical studies conducted, lease terms and management's future exploration plans. The cost of impairment is charged to expense in the period in which it occurs. Costs incurred for exploration dry holes, geological and geophysical work (including the cost of seismic data), and delay rentals are charged to expense as incurred. Costs of other property and equipment are depreciated on a straight-line basis based on their respective useful lives.
Asset Retirement Obligations	Asset Retirement Obligations
	The Company currently does not have any oil and natural gas production or any legal obligations to incur decommissioning costs. Should such production occur in the future, the Company expects to have significant obligations under its lease agreements and federal regulation to remove its equipment and restore land or seabed at the end of oil and natural gas production operations. These asset retirement obligations are primarily associated with plugging and abandoning wells and removing and disposing of offshore oil and natural gas platforms. Estimating the future restoration and removal cost is difficult and requires the Company to make estimates and judgments because most of the removal obligations are many years in the future and contracts and regulation often have vague descriptions of what constitutes removal. Asset removal technologies and cost are constantly changing, as are regulatory, political, environmental, safety and public relations considerations. Pursuant to the accounting guidance relating to "Asset Retirement Obligations", the Company is required to record a separate liability for the estimated fair value of its asset retirement obligations, with an offsetting increase to the related oil and natural gas properties representing asset retirement costs on its balance sheet. The cost of the related oil and natural gas asset, including the asset retirement cost, is depreciated over the useful life of the asset. The estimated fair value of asset retirement obligations is measured by reference to the expected future cash outflows required to satisfy the retirement obligation discounted at the Company's credit-adjusted risk-free interest rate. Accretion expense is recognized over time as the discounted liability is accreted to its expected settlement value.
	Inherent to the present value calculation are numerous estimates, assumptions and judgments, including the ultimate settlement amounts, inflation factors, credit adjusted risk-free rates, timing of settlement and changes in the legal, regulatory, environmental and political environments. To the extent future revisions to these assumptions impact the present value of the abandonment liability, the Company will make corresponding adjustments to both the asset retirement obligation and the related oil and natural gas property asset balance. Increases in the discounted abandonment liability and related oil and natural gas assets resulting from the passage of time will be reflected as additional accretion and depreciation expense in the consolidated statements of operations.
Inventory	Inventory
	Inventories consist of various tubular products that are used in the Company's drilling programs. The products are stated at the average cost. Cost is determined using a weighted average method comprised of the purchase price and other directly attributable costs.
Income Taxes	Income Taxes
	The Company applied the liability method of accounting for income taxes in accordance with accounting guidance related to "Income Taxes" as clarified by "Accounting for Uncertainty in Income Taxes." Under this method, deferred tax assets and liabilities are determined by applying tax rates in effect at the end of a reporting period to the cumulative temporary differences between the tax bases of assets and liabilities and their reported amounts in the financial statements. Since the Company currently has no production activities and there can be no assurance that the Company will generate any earnings or any specific level of earnings in future years, the Company has established a valuation allowance that equals its net deferred tax assets. See Note 16.
Equity-Based Compensation	Equity-Based Compensation
	The Company accounts for stock-based compensation at fair value. The Company grants various types of stock-based awards including stock options, restricted stock and performance-based awards. The fair value of stock option awards is determined using the Black-Scholes-Merton option-pricing model. For restricted stock awards with market conditions, the fair value of the awards is measured using the asset-or-nothing option pricing model. Restricted stock awards without market conditions and the performance-based awards are valued using the market price of the Company's common stock on the grant date. The Company records compensation cost, net of estimated forfeitures, on a straight-line basis for stock-based compensation awards over the requisite service period except for performance-based awards. For performance-based awards, compensation cost is recognized over the requisite service period as and when the Company determines that the achievement of the performance condition is probable, using the per-share fair value measured at grant date. See Note 14.
Earnings (Loss) Per Share	Earnings (Loss) Per Share
	Basic income (loss) per share was calculated by dividing net income or loss applicable to common shares by the weighted average number of common shares outstanding during the periods presented. The calculation of diluted income (loss) per share should include the potential dilutive impact of non-vested restricted shares, non-vested restricted stock units, outstanding stock options, the 2.625% convertible senior notes due 2019 and the 3.125% convertible senior notes due 2024, during the period, unless their effect is anti-dilutive. For the year ended December 31, 2014, 5,997,374 shares of non-vested restricted stock, non-vested restricted stock units, outstanding stock options, the 2.625% convertible senior notes due 2019 and the 3.125% convertible senior notes due 2024, were excluded from the diluted income (loss) per share because they are anti-dilutive. For the year ended December 31, 2013, 6,735,046 shares of non-vested restricted stock, non-vested restricted stock units, outstanding stock options and the 2.625% convertible senior notes due 2019 were excluded from the diluted income (loss) per share because they are anti-dilutive. For the year ended December 31, 2012, 5,617,697 shares of non-vested restricted stock, non-vested restricted stock units and outstanding stock options were excluded from the diluted income (loss) per share because they are anti-dilutive.
Operating Costs and Expenses	Operating Costs and Expenses
	Expenses consist primarily of the costs of acquiring and processing of geological and geophysical data, exploration, and appraisal drilling expenses, consultants, telecommunications, payroll and benefit costs, information system and legal costs, office rent, contract costs, and bookkeeping and audit fees.

Cash_and_Cash_Equivalents_Tabl

Cash and Cash Equivalents (Tables)	12 Months Ended
	Dec. 31, 2014
Cash and Cash Equivalents.
Cash and cash equivalents
			December 31,		December 31,
			2014		2013
			($ in thousands)
	Cash at banks		$	57,750	$	82,428
	Money market funds			122,218		75,039
	Held-to-maturity securities(1)			78,753		34,993
			$	258,721	$	192,460
	-1	These securities mature three months or less from date of purchase.

Restricted_Funds_Tables

Restricted Funds (Tables)	12 Months Ended
	Dec. 31, 2014
Restricted Funds
Schedule of restricted funds
			December 31,		December 31,
			2014		2013
			($ in thousands)
	Short-term:
	Collateral on letters of credit for Angola		$	45,062	$	200,339
			$	45,062	$	200,339
	Long-term:
	Collateral on letters of credit for Angola		$	105,051	$	104,496
			$	105,051	$	104,496
	Total restricted funds(1)		$	150,113	$	304,835
	-1	As of December 31, 2014 and 2013, $150.1 million and $304.8 million, respectively, was held in a collateral account established to secure letters of credit issued in support of the Company's contractually agreed work program obligations on Blocks 9, 20 and 21 offshore Angola. During the year ended December 31, 2014, restricted funds of $155.0 million were released to the Company in connection with completion of a portion of the agreed work program obligations on Block 20 and 21 offshore Angola. As of December 31, 2014, $45.1 million was reclassified from long-term restricted funds to short-term restricted funds in connection with the completion of a portion of the Company's agreed work program obligations on Block 9 and 21 offshore Angola. On February 5, 2015, restricted funds totaling $45.1 million were released to the Company in connection with completion of a portion of the work program obligations on Block 9 and completion of the remaining work program obligations on Block 21. The Block 21 letter of credit was therefore reduced to zero and cancelled effective February 10, 2015. As of December 31, 2014 and 2013, the collateral in this account was invested in U.S. Treasury bills and Treasury notes purchased at discounts and at premiums, respectively, resulting in a net carrying value of $150.1 million and $304.8 million, respectively. The contractual maturities of these securities are within one year.

Joint_Interests_and_Other_Rece1

Joint Interests and Other Receivables (Tables)	12 Months Ended
	Dec. 31, 2014
Joint Interest and Other Receivables
Schedule of joint interest and other receivables
		December 31,		December 31,
		2014		2013
		($ in thousands)
	Partners in the U.S. Gulf of Mexico	$	3,274	$	68,664
	Partners in West Africa		46,312		46,897
	Accrued interest on investment securities		7,663		5,632
	Other		2,725		3,446
		$	59,974	$	124,639

Prepaid_Expenses_and_Other_Cur1

Prepaid Expenses and Other Current Assets (Tables)	12 Months Ended
	Dec. 31, 2014
Prepaid Expenses and Other Current Assets
Schedule of prepaid expenses and other current assets
			December 31,		December 31,
			2014		2013
			($ in thousands)
	Prepaid expenses:
	Prepaid expenses(1)		$	6,273	$	37,796
	Other current assets:
	Cash advance to joint venture partner(2)			—		9,685
	Rig mobilization, regulatory and other related costs(3)			8,224		8,376
			$	14,497	$	55,857
	-1	As of December 31, 2014, prepaid expenses include $6.3 million of the prepaid and unamortized portion of payments made for software licenses, related maintenance fees and insurance. As of December 31, 2013, prepaid expenses include $11.5 million of the prepaid and unamortized portion of payments made for software licenses, related maintenance fees, insurance and $26.3 million of prepaid costs associated with the Ensco drilling rig contract. The drilling rig contract terminated in January 2014 and upon receipt and application of prepaid amounts against the final invoice from Ensco, any remaining balance of the prepayment was refunded to the Company.
	-2	As of December 31, 2013, the $9.7 million in other current assets relates to payment of cash calls made to our joint interest partner, Total Gabon, for operating costs to drill the Diaman #1B exploration well. This prepayment was applied against the joint interest bills upon receipt from Total Gabon as of December 31, 2014.
	-3	As of December 31, 2014 and 2013, the $8.2 million and $8.4 million, respectively, in other current assets relates to the short-term portion of the mobilization and regulatory acceptance testing costs associated with the SSV Catarina drilling rig and the Rowan Reliance drilling rig.

Investments_Tables

Investments (Tables)	12 Months Ended
	Dec. 31, 2014
Investments
Schedule of fair value of held-to-maturity securities recorded at amortized cost
		December 31,		December 31,
		2014		2013
		($ in thousands)
	U.S. Treasury bills	$	46,064	$	304,834
	U.S. Treasury notes		104,049		—
	Corporate securities		1,321,261		856,002
	Commercial paper		483,534		408,033
	U.S. Agency securities		24,996		—
	Certificates of deposit		105,215		105,000
	Total	$	2,085,119	$	1,673,869
Schedule of held-to-maturity securities included in the company's consolidated balance sheet
		December 31,		December 31,
		2014		2013
		($ in thousands)
	Cash and cash equivalents	$	78,753	$	34,993
	Short-term investments		1,530,206		1,319,380
	Short-term restricted funds		45,062		200,339
	Long-term restricted funds		105,051		104,496
	Long-term investments		326,047		14,661
		$	2,085,119	$	1,673,869
Schedule of contractual maturities of held-to-maturity securities
		December 31, 2014				December 31, 2013
		Carrying		Estimated		Carrying		Estimated
		Value		Fair Value		Value		Fair Value
		($ in thousands)
	Within 1 year	$	1,759,072	$	1,759,072	$	1,659,208	$	1,659,208
	After 1 year		326,047		326,047		14,661		14,661
		$	2,085,119	$	2,085,119	$	1,673,869	$	1,673,869

Fair_Value_Measurement_Tables

Fair Value Measurement (Tables)	12 Months Ended
	Dec. 31, 2014
Fair Value Measurements
Significant financial instruments as categorized by the fair value measurement hierarchy
			Level 1				Level 2
			Carrying		Fair		Carrying		Fair		Balance as of
			Value		Value(1)		Value		Value(1)		December 31,
											2014
			($ in thousands)
	Cash and cash equivalents:
	Cash		$	57,750	$	57,750	$	—	$	—	$	57,750
	Money market funds			122,218		122,218						122,218
	Commercial paper			—		—		70,524		70,524		70,524
	Corporate bonds			—		—		8,229		8,229		8,229
	Subtotal			179,968		179,968		78,753		78,753		258,721
	Short-term restricted funds:
	U.S. Treasury bills			—		—		45,062		45,062		45,062
	Subtotal			—		—		45,062		45,062		45,062
	Short-term investments:
	U.S. Agency securities			—		—		24,996		24,996		24,996
	Corporate bonds			—		—		986,985		986,985		986,985
	Commercial paper			—		—		413,010		413,010		413,010
	Certificates of deposits			—		—		105,215		105,215		105,215
	Subtotal			—		—		1,530,206		1,530,206		1,530,206
	Long-term restricted funds:
	U.S. Treasury bills			—		—		1,002		1,002		1,002
	U.S. Treasury notes			—		—		104,049		104,049		104,049
	Subtotal			—		—		105,051		105,051		105,051
	Long-term investments:
	Corporate bonds			—		—		326,047		326,047		326,047
	Subtotal			—		—		326,047		326,047		326,047
	Total		$	179,968	$	179,968	$	2,085,119	$	2,085,119	$	2,265,087
			Level 1				Level 2
			Carrying		Fair		Carrying		Fair		Balance as of
			Value		Value(1)		Value		Value(1)		December 31,
											2013
			($ in thousands)
	Cash and cash equivalents:
	Cash		$	82,428	$	82,428	$	—	$	—	$	82,428
	Money market funds			75,039		75,039		—		—		75,039
	Commercial paper			—		—		9,993		9,993		9,993
	Certificate of deposits			—		—		25,000		25,000		25,000
	Subtotal			157,467		157,467		34,993		34,993		192,460
	Short-term restricted funds:
	U.S. Treasury notes			—		—		200,339		200,339		200,339
	Subtotal			—		—		200,339		200,339		200,339
	Short-term investments:
	Corporate bonds			—		—		848,307		848,307		848,307
	Commercial paper			—		—		391,073		391,073		391,073
	Certificates of deposits			—		—		80,000		80,000		80,000
	Subtotal			—		—		1,319,380		1,319,380		1,319,380
	Long-term restricted funds:
	U.S. Treasury notes			—		—		104,496		104,496		104,496
	Subtotal			—		—		104,496		104,496		104,496
	Long-term investments:
	Commercial paper			—		—		6,967		6,967		6,967
	Corporate bonds			—		—		7,694		7,694		7,694
	Subtotal			—		—		14,661		14,661		14,661
	Total		$	157,467	$	157,467	$	1,673,869	$	1,673,869	$	1,831,336
	-1	As of December 31, 2014 and 2013, the Company did not record any OTTI on these assets.

Property_Plant_and_Equipment_T

Property, Plant, and Equipment (Tables)	12 Months Ended
	Dec. 31, 2014
Property, Plant, and Equipment
Schedule of Property, Plant, and Equipment
			Estimated		December 31,			December 31,
			Useful Life		2014			2013
			(Years)
					($ in thousands)
	Oil and Gas Properties:
	Proved properties:
	Well and development costs				$	183,221		$	92,579
	Total proved properties					183,221			92,579
	Unproved properties:
	Oil and gas leasehold					762,518			754,894
	Less: accumulated valuation allowance					(211,224	)		(160,913	)
						551,294			593,981
	Exploration wells in process					1,186,464			777,823
	Total unproved properties					1,737,758			1,371,804
	Total oil and gas properties, net					1,920,979			1,464,383
	Other Property and Equipment:
	Computer equipment and software		3			5,672			5,115
	Office equipment and furniture		3 - 5			2,139			2,132
	Vehicles		3			265			265
	Leasehold improvements		3 - 10			2,488			2,456
	Running tools and equipment		3			9,795			6,318
						20,359			16,286
	Less: accumulated depreciation and amortization					(8,977	)		(4,394	)
	Total other property and equipment, net					11,382			11,892
	Property, plant, and equipment, net				$	1,932,361		$	1,476,275
Schedule of unproved property acquisition costs, net of valuation allowance
			December 31,			December 31,
			2014			2013
			($ in thousands)
	U.S. Gulf of Mexico:
	Individual oil and gas leaseholds with carrying value greater than $1 million		$	320,731		$	328,128
	Individual oil and gas leaseholds with carrying value less than $1 million			83,916			68,895
				404,647			397,023
	Accumulated valuation allowance & impairment			(208,724	)		(160,913	)
				195,923			236,110
	West Africa:
	Blocks 9, 20 and 21 offshore Angola			355,876			355,876
	Diaba Block offshore Gabon			1,995			1,995
				357,871			357,871
	Accumulated impairment			(2,500	)		—
				355,371			357,871
	Total oil and gas leasehold		$	551,294		$	593,981
Schedule of net changes in capitalized exploration well costs
			December 31,			December 31,			December 31,
			2014			2013			2012
			($ in thousands)
	Beginning of period		$	777,823		$	451,024		$	178,338
	Additions to capitalized exploration
	U.S. Gulf of Mexico:
	Exploration well costs			143,431			154,877			178,295
	Capitalized interest			6,965			3,928			—
	West Africa:
	Exploration well costs			379,461			457,608			168,309
	Capitalized interest			44,243			12,271			—
	Reclassifications to wells, facilities, and equipment based on determination of proved reserves			—			(38,446	)		—
	Amounts charged to expense(1)			(165,459	)		(263,439	)		(73,918	)
	End of period		$	1,186,464		$	777,823		$	451,024
	-1	The amount of $165.5 million for the year ended December 31, 2014 represents $64.3 million of impairment charges on exploration wells drilled in the U.S. Gulf of Mexico and $101.2 million of impairment charges on exploration wells drilled offshore Angola, all of which did not encounter commercial hydrocarbons. The amount of $263.4 million for the year ended December 31, 2013 represents $120.0 million of impairment charges on exploration wells drilled in the U.S. Gulf of Mexico which did not encounter commercial hydrocarbons, $126.3 million of impairment charges on exploration wells drilled offshore Angola which failed to flow measurable hydrocarbons from drill stem tests and a portion of the cost of exploration wells drilled offshore Angola that were determined to have no utility in the lowest interval beneath the pay zone and $17.1 million of impairment charges on the exploration well drilled offshore Gabon which needed to be re-spud due to mechanical problems with the wellbore.
Schedule of cumulative costs of capitalized exploration well costs
			December 31,			December 31,
			2014			2013
			($ in thousands)
	Cumulative costs:
	U.S. Gulf of Mexico
	Exploration well costs		$	283,885		$	204,707
	Capitalized interest			10,894			3,928
	West Africa
	Exploration well costs			835,171			556,917
	Capitalized interest			56,514			12,271
			$	1,186,464		$	777,823
	Well costs capitalized for a period greater than one year after completion of drilling (included in the table above) are summarized as follows:
			Year Ended December 31,
			2014			2013			2012
			($ in thousands)
	U.S. Gulf of Mexico		$	208,634		$	186,510		$	89.490
	West Africa			566,745			213,265			105,363
			$	775,379		$	399,775		$	194,853
	Number of projects with exploration well costs that have been capitalized more than a year			8			3			3

Other_Assets_Table

Other Assets (Table)	12 Months Ended
	Dec. 31, 2014
Other Assets
Schedule of other assets
			December 31,
			2014		2013
			($ in thousands)
	Debt issue cost(1)		$	36,708	$	20,983
	Long-term portion of prepaid shorebase leases			2,244		3,241
	Rig mobilization costs(2)			14,984		11,153
	Long-term accounts receivable(3)			—		17,923
	Other			—		437
			$	53,936	$	53,737
	-1	As of December 31, 2014, the $36.7 million in debt issue costs included $18.5 million and $18.2 million in costs related to the issuance of the Company's 2.625% convertible senior notes due 2019 and the Company's 3.125% convertible senior notes due 2024, respectively, as described in Note 10—Long-term Debt. As of December 31, 2013, the $21.0 million in debt issue costs was related to the issuance of the Company's 2.625% convertible senior notes due 2019 as described in Note 10—Long-term Debt. These debt issue costs are amortized over the life of the notes using the effective interest method.
	-2	As of December 31, 2014 and 2013, the $15.0 million and $11.2 million, respectively, relate to costs associated with the long-term mobilization and the regulatory acceptance testing of the SSV Catarina drilling rig which is currently drilling in West Africa, and costs relating to the Rowan Reliance drilling rig which was delivered in January 2015 and is currently drilling our North Platte #2 appraisal well. These costs are or will be amortized over the term of the drilling rig contracts.
	-3	As of December 31, 2013, the $17.9 million of long-term accounts receivable was related to a 3.75% cost interest disputed by one of our former partners on Block 9 and 21 offshore Angola. On October 30, 2014, the Company collected the entire balance due from the Company's partner on Block 9 and 21.

Longterms_Debt_Tables

Long-terms Debt (Tables)	12 Months Ended
	Dec. 31, 2014
Long-term Debt
Schedule of the carrying amounts of the liability components of the Notes
			December 31, 2014								December 31, 2013
			Principal			Unamortized			Carrying		Principal		Unamortized			Carrying
			Amount			discount(1)			Amount		Amount		discount			Amount
			($ in thousands)
	Carrying amount of liability component
	2.625% Notes		$	1,380,000		$	(295,509	)	$	1,084,491	$	1,380,000	$	(344,020	)	$	1,035,980
	3.125% Notes			1,300,000			(455,963	)		844,037		—		—			—
	Total		$	2,680,000		$	(751,472	)	$	1,928,528	$	1,380,000	$	(344,020	)	$	1,035,980
	-1	Unamortized discount will be amortized over the remaining life of the Notes which is 5 years for the 2.625% Notes and 9.50 years for the 3.125% Notes.
Schedule of carrying amounts of the equity components of the Notes
			December 31,			December 31,
			2014			2013
			($ in thousands)
	Debt discount relating to value of conversion option		$	866,340		$	390,540
	Debt issue costs			(20,185	)		(9,124	)
	Total		$	846,155		$	381,416
Schedule of fair value of Notes
			December 31,			December 31,
			2014			2013
			($ in thousands)
	2.625% Notes		$	1,361,000		$	1,227,000
	3.125% Notes			1,047,000			—
	Total		$	2,408,000		$	1,227,000
Schedule of interest expense
			For Year Ended December 31,
			2014			2013			2012
			($ in thousands)
	Interest expense associated with accrued interest(1)		$	3,271		$	18,529		$	1,294
	Interest expense associated with accretion of debt discount			68,348			44,789			1,843
	Interest expense associated with amortization of debt issue costs			3,149			2,058			75
			$	74,768		$	65,376		$	3,212
	-1	The $3.3 million, $18.5 million and $1.3 million for the years ended December 31, 2014, 2013 and 2012, respectively, represent interest expense net of capitalized amounts of $58.5 million, $17.7 million and $0 million, respectively.

Contractual_Obligations_Tables

Contractual Obligations (Tables)	12 Months Ended
	Dec. 31, 2014
Contractual Obligations
Summary of components of short-term and long-term contractual obligations
			December 31,		December 31,
			2014		2013
			($ in thousands)
	Short-term Contractual Obligations:
	Social obligation payments for Block 9, offshore Angola		$	560	$	150
	Social obligation payments for Block 21, offshore Angola			1,156		300
	Social obligation and bonus payments for Block 20, offshore Angola(1)			48,569		48,569
			$	50,285	$	49,019
	Long-term Contractual Obligations:
	Social and work program obligation payments for Block 9, offshore Angola		$	21,875	$	669
	Social obligation payments for Block 21, offshore Angola			74		1,381
	Social obligation and bonus payments for Block 20, offshore Angola(1)			79,996		122,851
			$	101,945	$	124,901
	-1	The total amount of $128.6 million under social obligation payments for Block 20 has been capitalized in unproved oil and gas leasehold. See Note 8—Property, Plants and Equipment.

Seismic_and_Exploration_Expens1

Seismic and Exploration Expenses (Tables)	12 Months Ended
	Dec. 31, 2014
Seismic and Exploration Expenses
Schedule of seismic and exploration expenses
		For Year Ended December 31,
		2014		2013		2012
		($ in thousands)
	Seismic costs	$	34,359	$	63,721	$	42,447
	Leasehold delay rentals		7,391		6,660		6,383
	Drilling rig expense and other exploration expense		43,817		3,832		12,753
		$	85,567	$	74,213	$	61,583

Equity_based_Compensation_Tabl

Equity based Compensation (Tables)	12 Months Ended
	Dec. 31, 2014
Equity Based Compensation
Schedule of restricted stock awarded to employees and restricted stock units
			Year Ended December 31,
			2014					2013					2012
			Restricted			Weighted		Restricted			Weighted		Restricted			Weighted
			Shares			Average		Shares			Average		Shares			Average
						Grant Date					Grant Date					Grant Date
						Fair Value					Fair Value					Fair Value
						Per Share					Per Share					Per Share
	Non-vested shares at beginning of year			4,334,886		$	14.31		4,040,825		$	13.05		4,599,783		$	11.27
	Granted			2,275,317		$	14.53		620,840		$	24.58		487,710		$	26.01
	Vested			(1,433,172	)	$	16.32		(239,317	)	$	17.37		(738,628	)	$	13.05
	Forfeited or expired(1)			(2,374,242	)	$	10.63		(87,462	)	$	20.91		(308,040	)	$	12.17
	Non-vested shares at end of year			2,802,789		$	16.44		4,334,886		$	14.31		4,040,825		$	13.05
	Weighted-average vesting period remaining			3.08 years					1.22 years					1.87 years
	Unrecognized compensation ($ in thousands)		$	34,066				$	22,467				$	23,827
	-1	The 2,374,242 forfeited or expired restricted shares for the year ended December 31, 2014 include 2,306,173 restricted shares that were forfeited on December 21, 2014 because the market condition attached to the vesting terms of the awards was not met.
Schedule of assumptions used to determine the fair value of each stock option granted using the Black-Scholes-Merton option-pricing model
			2014
	Expected Term in Years			5.5
	Expected Volatility			57.27	%
	Expected Dividends			—	%
	Risk-Free Interest Rate			1.69	%
Schedule of stock option activities
			Shares			Weighted		Weighted-Average			Aggregate
						Average		Remaining			Intrinsic Value
						Exercise		Contractual Term			(thousands)
						Price		(years)
	Outstanding at January 1, 2014			2,338,718		$	20.24		8		$	—
	Granted			812,055		$	17.5
	Exercised			(3,005	)	$	12.45				$	17,837
	Forfeited or expired			(11,221	)	$	24.02
	Outstanding at December 31, 2014			3,136,547		$	19.52		7.57		$	—
	Vested or expected to vest at December 31, 2014			1,693,193		$	20.82		8.61		$	—
	Exercisable at December 31, 2014			1,411,271		$	17.93		6.3		$	—
Schedule of recognized equity-based compensation costs
			Year Ended December 31,
			2014			2013		2012
			($ in thousands)
	Restricted stock:
	Employees		$	20,971		$	15,470	$	13,378
	Non-employee directors			1,476			1,260		970
	Stock options:
	Employees			9,295			7,405		3,790
	Restricted stock units (performance-based)			—			4,619		4,272
			$	31,742		$	28,754	$	22,410
Restricted stock units
Equity Based Compensation
Schedule of stock option activities
			Year Ended December 31,
			2014					2013					2012
			Number of			Weighted		Number of			Weighted		Number of			Weighted
			shares			Average		shares			Average		shares			Average
			relating			Grant Date		relating			Grant Date		relating			Grant Date
			Restricted			Fair Value		Restricted			Fair Value		Restricted			Fair Value
			Stock Units			Per Unit		Stock Units			Per Unit		Stock Units			Per Unit
	Non-vested at beginning of year			21,624		$	30.5		109,275		$	30.5		198,838		$	12.45
	Granted			—			—		—			—		—			—
	Vested			(21,624	)	$	30.5		(87,401	)	$	30.5		(74,537	)	$	30.5
	Forfeited or expired			—			—		(250	)	$	30.5		(15,026	)	$	30.5
	Non-vested at end of year			—			—		21,624		$	30.5		109,275		$	30.5
	Weighted-average period remaining			—					—					1 year

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Taxes
Schedule of components of the income tax provision (benefit)
			Year Ended
			December 31,
			2014			2013			2012
			($ in thousands)
	Current taxes:
	U.S. federal		$	—		$	—		$	—
	Foreign			—			—			—
	Deferred taxes:
	U.S. federal			—			—			—
	Foreign			—			—			—
	Total		$	—		$	—		$	—
Schedule of net income pre or post of corporate reorganization
			Year Ended December 31,
			2014			2013			2012
			($ in thousands)
	U.S.:
	Net income (loss) as reported		$	(307,025	)	$	(387,210	)	$	(229,372	)
	Less: net income (loss) applicable to period before corporate reorganization			—			—			—
	Foreign:
	Net income (loss) as reported			(203,738	)		(201,814	)		(53,627	)
	Less: net income (loss) applicable to period before corporate reorganization			—			—			—
	Net income (loss) applicable to period after corporate reorganization		$	(510,763	)	$	(589,024	)	$	(282,999	)
Schedule of effective income tax reconciliation
			Year Ended December 31,
			2014						2013					2012
			($ in thousands)
	Income tax expense (benefit) at the federal statutory rate		$	(178,767	)		35	%	$	(206,159	)	35	%	$	(99,050	)	35	%
	State income taxes, net of federal income tax benefit			(828	)		0.2	%		(489	)	0.1	%		(512	)	0.2	%
	Foreign income tax			(111,151	)		21.8	%		(70,994	)	12.1	%		4,447		–1.6	%
	Other			9,098			–1.8	%		366		–0.1	%		2,678		–0.9	%
	Valuation allowance(1)			281,648			–55.2	%		277,276		–47.1	%		92,437		–32.7	%
			$	—			—	%	$	—		—	%	$	—		—	%
	-1	The change in the deferred tax asset valuation allowance of $277.3 million for the year end December 31, 2013, excludes a $85.3 million net decrease in valuation allowance due to previously unrecorded foreign deferred tax assets and a deferred tax liability related to the Company's convertible debt instrument that did not impact the rate reconciliation.
Schedule of Company's deferred tax assets and liabilities
			As of December 31,
			2014			2013
			($ in thousands)
	Short-term deferred tax liabilities:
	2.625% convertible senior notes due 2019(1)		$	18,479		$	17,061
	3.125% convertible senior notes due 2024(1)			11,855			—
	Total short-term deferred tax liabilities			30,334			17,061
	Long-term deferred tax liabilities:
	2.625% convertible senior notes due 2019		$	85,471		$	103,951
	3.125% convertible senior notes due 2024			148,507			—
	Oil and gas properties			54,461			22,135
	Total long-term deferred tax liabilities			288,439			126,086
	Long-term deferred tax assets:
	Seismic and exploration costs			457,854			280,095
	Stock based compensation			18,092			20,842
	Domestic NOL carry forwards			415,608			273,163
	Foreign NOL carry forwards			38,200			28,633
	Other			(43,021	)		1,976
	Valuation allowance			(567,960	)		(461,562	)
	Total long-term deferred assets			318,773			143,147
	Net long-term deferred assets			30,334			17,061
	Net deferred tax assets		$	—		$	—
	-1	The recognition of the liability and equity components of the debt resulted in a taxable temporary basis difference and recorded as an adjustment to additional paid-in capital.

Commitments_Tables

Commitments (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments
Schedule of payments due for the estimated commitments, excluding long-term debt
			Payments Due By Year
			2015		2016		2017		2018		2019		Thereafter
			($ in thousands)
	Drilling Rig and Related Contracts		$	544,559	$	299,702	$	208,104	$	17,104	$	—	$	—
	Operating Leases			9,755		4,801		2,309		2,369		2,405		5,626
	Lease Rentals(1)			7,353		5,460		5,007		2,282		1,973		7,223
	Social and Work Program Payment Obligations(2)			55,999		84,729		5,714		5,714		—		—
	Total		$	617,666	$	394,692	$	221,134	$	27,469	$	4,378	$	12,849
	-1	Relates to the annual delay rental payments payable to the Office of Natural Resources Revenue within the U.S. Department of the Interior with respect to the Company's U.S. Gulf of Mexico leases. These annual payments are required to maintain the leases from year to year.
	-2	Includes the Company's contractual payment obligations for (i) social projects such as the Sonangol Research and Technology Center and academic scholarships for Angolan students that the Company was and is contractually obligated to pay in consideration for the Angolan government granting it the licenses to explore for and develop hydrocarbons offshore Angola and (ii) the Company's remaining work program obligations on Block 9 offshore Angola. Pursuant to the terms of the Risk Services Agreements for Blocks 9 and 21 and the Production Sharing Agreement for Block 20, the Company is not required to pay annual rental payments to maintain the licenses from year to year.

Segment_Information_Tables

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2014
Segment Information
Schedule of segment information by geographic operating segment
			United States			West Africa			Total
			($ in thousands)
	Year ended December 31, 2014
	Operating costs and expense		$	238,214		$	203,727		$	441,941
	Operating income (loss)			(238,214	)		(203,727	)		(441,941	)
	Other income (expense)									(68,822	)
	Net income (loss)								$	(510,763	)
	Additions to Property and Equipment, net(1)		$	135,449		$	320,637		$	456,086
	Year ended December 31, 2013
	Operating costs and expense		$	329,832		$	202,852		$	532,684
	Operating income (loss)			(329,832	)		(202,852	)		(532,684	)
	Other income (expense)									(56,340	)
	Net income (loss)								$	(589,024	)
	Additions to Property and Equipment, net(1)		$	44,124		$	332,395		$	376,519
	Year ended December 31, 2012
	Operating costs and expense		$	231,196		$	53,632		$	284,828
	Operating income (loss)			(231,196	)		(53,632	)		(284,828	)
	Other income (expense)									1,829
	Net income (loss)								$	(282,999	)
	Additions to Property and Equipment, net(1)		$	67,068		$	169,362		$	236,430
	-1	These amounts are net of accumulated allowance for impairment on oil and gas properties and accumulated depreciation and amortization on other property and equipment.

Selected_Quarterly_Financial_D1

Selected Quarterly Financial Data-Unaudited (Tables)	12 Months Ended
	Dec. 31, 2014
Selected Quarterly Financial Data-Unaudited
Schedule of Selected Quarterly Financial Data Unaudited
			1st Quarter			2nd Quarter			3rd Quarter			4th Quarter
			($ in thousands, except per share data)
	Year ended December 31, 2014
	Operating costs and expenses		$	47,293		$	77,591		$	120,961		$	196,097
	Operating income (loss)			(47,293	)		(77,591	)		(120,961	)		(196,097	)
	Net income (loss)			(56,915	)		(94,756	)		(142,529	)		(216,564	)
	Basic and diluted income (loss) per common share(1)		$	(0.14	)	$	(0.23	)	$	(0.35	)	$	(0.53	)
	Year ended December 31, 2013
	Operating costs and expenses		$	112,452		$	65,365		$	145,663		$	209,204
	Operating income (loss)			(112,452	)		(65,365	)		(145,663	)		(209,204	)
	Net income (loss)			(128,087	)		(78,818	)		(160,000	)		(222,119	)
	Basic and diluted income (loss) per common share(1)		$	(0.31	)	$	(0.19	)	$	(0.39	)	$	(0.55	)
	-1	Totals may not add due to rounding.

Supplemental_Information_on_Oi1

Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited)
Schedule of Capitalized Costs Related to Oil and Gas Activities
			U.S. Gulf			West Africa			Total
			of Mexico
			($ in thousands)
	As of December 31, 2014
	Unproved properties(1)		$	699,426		$	1,249,556		$	1,948,982
	Accumulated valuation allowance			(208,724	)		(2,500	)		(211,224	)
				490,702			1,247,056			1,737,758
	Proved properties			183,221			—			183,221
	Net capitalized costs		$	673,923		$	1,247,056		$	1,920,979
	As of December 31, 2013
	Unproved properties		$	605,658		$	927,059		$	1,532,717
	Accumulated valuation allowance			(160,913	)		—			(160,913	)
				444,745			927,059			1,371,804
	Proved properties			92,579			—			92,579
	Net capitalized costs		$	537,324		$	927,059		$	1,464,383
	-1	Unproved properties include capitalized costs net of sale/like-kind exchange of leasehold interest transactions that occurred in 2014 and 2013 of approximately $5.6 million and $10.7 million, respectively, for the U.S. Gulf of Mexico. No gain or loss was recognized for these transactions for the years ended December 31, 2014 and 2013.
Schedule of Costs Incurred in Oil and Gas Activities
			U.S. Gulf			West Africa			Total
			of Mexico
			($ in thousands)
	Year ended December 31, 2014
	Property acquisition
	Unproved		$	27,784		$	—		$	27,784
	Proved			—			—			—
	Exploration
	Capitalized			150,396			423,704			574,100
	Expensed			31,531			54,036			85,567
	Development			90,642			—			90,642
	Total Costs Incurred		$	300,353		$	477,740		$	778,093
	Year ended December 31, 2013
	Property acquisition
	Unproved		$	37,584		$	—		$	37,584
	Proved			—			—			—
	Exploration
	Capitalized			158,806			469,879			628,685
	Expensed			48,688			25,525			74,213
	Development			54,133			—			54,133
	Total Costs Incurred		$	299,211		$	495,404		$	794,615
	Year ended December 31, 2012
	Property acquisition
	Unproved		$	19,961		$	—		$	19,961
	Proved			—			—			—
	Exploration
	Capitalized			178,295			168,309			346,604
	Expensed			32,874			28,709			61,583
	Development			—			—			—
	Total Costs Incurred		$	231,130		$	197,018		$	428,148
Schedule of reserve quantity information
			Natural Gas			Oil and			Equivalent
			(in Bcf)			Condensate			Volumes
						(in MMBbls)			(in MMBOE)
	Proved undeveloped reserves:
	Balance at December 31, 2012			—			—			—
	Discoveries			3.4			7.9			8.5
	Balance at December 31, 2013			3.4			7.9			8.5
	Revisions			0.3			0.5			0.5
	Balance at December 31, 2014			3.7			8.4			9.0
Schedule of the Company's estimated discounted future net cash flows related to its proved natural gas reserves
			2014			2013
			($ in thousands)
	Future cash inflows		$	814,394		$	830,287
	Future production costs			(12,710	)		(6,400	)
	Future development costs			(244,306	)		(302,278	)
	Future income tax expense(1)			—			—
	Future net cash flows			557,378			521,609
	10% annual discount for estimated timing of cash flows			(192,094	)		(244,976	)
	Standardized measure of discounted future net cash flows		$	365,284		$	276,633
	-1	There is no future income tax expense as of December 31, 2014, as the tax basis of the oil and gas properties in the United States and net operating losses attributable to oil and gas operations exceed the future net revenues.
Schedule of information with respect to the company's standardized measure of discounted future net cash flows
			2014			2013
			($ in thousands)
	Standardized measure, beginning		$	276,633		$	—
	Discoveries			—			276,633
	Revisions of previous estimates:			—			—
	Changes in prices and costs			(36,869	)		—
	Changes in future development costs			49,700			—
	Changes in quantities			17,351			—
	Accretion of discount			27,663			—
	Changes in timing and other			30,806			—
	Standardized measure, ending		$	365,284		$	276,633

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 17, 2012	13-May-14
Revenue Recognition
Oil and gas revenue	$0	$0	$0
Investments
OTTI in debt securities	$0	$0
Joint Interest and Other Receivables
Settlement period of receivables, maximum	30 days
Earnings (Loss) Per Share
Shares of non-vested restricted stock, non vested restricted stock units, outstanding stock options and 2.625% convertible senior notes due 2019 and 3.125% convertible senior notes due 2024 excluded from the diluted income (loss) per share calculation	5,997,374	6,735,046	5,617,697
Earnings (Loss) Per Share
Interest rate (as a percent)	3.13%		2.63%
2.625% convertible senior notes due 2019
Earnings (Loss) Per Share
Interest rate (as a percent)	2.63%	2.63%	2.63%	2.63%
3.125% convertible senior notes due 2024
Earnings (Loss) Per Share
Interest rate (as a percent)	3.13%				3.13%

Cash_and_Cash_Equivalents_Deta

Cash and Cash Equivalents (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Cash and Cash Equivalents.
Cash at banks	$57,750	$82,428
Money market funds	122,218	75,039
Held-to-maturity securities	78,753	34,993
Total	$258,721	$192,460	$1,425,815	$292,546

Restricted_Funds_Details

Restricted Funds (Details) (USD $)	12 Months Ended	0 Months Ended
	Dec. 31, 2014	Feb. 05, 2015	Dec. 31, 2013
Restricted Funds
Short-term restricted funds	$45,062,000		$200,339,000
Long-term restricted funds	105,051,000		104,496,000
Block 20 And 21, Offshore Angola
Restricted Funds
Restricted fund released	155,000,000
Block 9 And 21 Offshore Angola
Restricted Funds
Restricted fund released		45,100,000
Amount reclassified from long-term restricted funds to short- term restricted funds	45,100,000
Collateral on letters of credit for Angola
Restricted Funds
Short-term restricted funds	45,062,000		200,339,000
Long-term restricted funds	105,051,000		104,496,000
Collateral held	150,113,000		304,835,000
Maturity period of investments	1 year
Collateral on letters of credit for Angola | U.S. Treasury bills
Restricted Funds
Net carrying value of investments invested through the funds	150,100,000
Collateral on letters of credit for Angola | U.S. Treasury notes
Restricted Funds
Net carrying value of investments invested through the funds			$304,800,000

Joint_Interests_and_Other_Rece2

Joint Interests and Other Receivables (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Joint Interest Receivables
Accrued interest on investment securities	$7,663	$5,632
Other	2,725	3,446
Total	59,974	124,639
Settlement period for bills under operating agreements	30 days
Partners in the U.S. Gulf of Mexico
Joint Interest Receivables
Receivable attributable to joint interest partners	3,274	68,664
Partners in West Africa
Joint Interest Receivables
Receivable attributable to joint interest partners	$46,312	$46,897

Prepaid_Expenses_and_Other_Cur2

Prepaid Expenses and Other Current Assets (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Prepaid expenses:
Prepaid expenses	$6,273,000	$37,796,000
Other current assets:
Cash advance to joint venture partner		9,685,000
Rig mobilization, regulatory and other related costs	8,224,000	8,376,000
Prepaid expenses and other current assets	14,497,000	55,857,000
Unamortized portion of payments made for software licenses included in prepaid expenses	6,300,000	11,500,000
Lease costs associated with Ensco drilling rig contract included in prepaid expenses		$26,300,000

Investments_Details

Investments (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Investments
Fair market value	$2,085,119	$1,673,869
Held-to-maturities, Carrying value
Within 1 year	1,759,072	1,659,208
After 1 year	326,047	14,661
Total	2,085,119	1,673,869
Held-to-maturity securities, Estimated fair value
Within 1 year	1,759,072	1,659,208
After 1 year	326,047	14,661
Total	2,085,119	1,673,869
Cash and cash equivalents
Investments
Fair market value	78,753	34,993
Held-to-maturity securities, Estimated fair value
Total	78,753	34,993
Short-term investments
Investments
Fair market value	1,530,206	1,319,380
Held-to-maturity securities, Estimated fair value
Total	1,530,206	1,319,380
Short-term restricted funds
Investments
Fair market value	45,062	200,339
Held-to-maturity securities, Estimated fair value
Total	45,062	200,339
Long-term restricted funds
Investments
Fair market value	105,051	104,496
Held-to-maturity securities, Estimated fair value
Total	105,051	104,496
Long-term investments
Investments
Fair market value	326,047	14,661
Held-to-maturity securities, Estimated fair value
Total	326,047	14,661
U.S. Treasury bills.
Investments
Fair market value	46,064	304,834
Held-to-maturity securities, Estimated fair value
Total	46,064	304,834
U.S. Treasury notes
Investments
Fair market value	104,049
Held-to-maturity securities, Estimated fair value
Total	104,049
Corporate securities
Investments
Fair market value	1,321,261	856,002
Held-to-maturity securities, Estimated fair value
Total	1,321,261	856,002
Commercial paper
Investments
Fair market value	483,534	408,033
Held-to-maturity securities, Estimated fair value
Total	483,534	408,033
US Agency Securities
Investments
Fair market value	24,996
Held-to-maturity securities, Estimated fair value
Total	24,996
Certificates of deposit
Investments
Fair market value	105,215	105,000
Held-to-maturity securities, Estimated fair value
Total	$105,215	$105,000

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	$258,721	$192,460	$1,425,815	$292,546
Short-term restricted funds	45,062	200,339
Short-term investments	1,530,206	1,319,380
Long-term restricted funds	105,051	104,496
Long-term investments	326,047	14,661
Total	2,265,087	1,831,336
Cash. | Recurring basis
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	57,750	82,428
Money market funds | Recurring basis
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	122,218	75,039
Commercial paper | Recurring basis
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	70,524	9,993
Short-term investments	413,010	391,073
Long-term investments		6,967
Corporate securities | Recurring basis
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	8,229
Short-term investments	986,985	848,307
Long-term investments	326,047	7,694
US Agency Securities
Significant financial instruments as categorized by the fair value measurement hierarchy
Short-term investments	24,996
U.S. Treasury bills
Significant financial instruments as categorized by the fair value measurement hierarchy
Long-term restricted funds	1,002
U.S. Treasury bills | Recurring basis
Significant financial instruments as categorized by the fair value measurement hierarchy
Short-term restricted funds	45,062
U.S. Treasury notes | Recurring basis
Significant financial instruments as categorized by the fair value measurement hierarchy
Short-term restricted funds		200,339
Long-term restricted funds	104,049	104,496
Certificates of deposit | Recurring basis
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents		25,000
Short-term investments	105,215	80,000
Level 1 | Recurring basis | Carrying Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	179,968	157,467
Total	179,968	157,467
Level 1 | Recurring basis | Fair Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	179,968	157,467
Total	179,968	157,467
Level 1 | Cash. | Recurring basis | Carrying Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	57,750	82,428
Level 1 | Cash. | Recurring basis | Fair Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	57,750	82,428
Level 1 | Money market funds | Recurring basis | Carrying Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	122,218	75,039
Level 1 | Money market funds | Recurring basis | Fair Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	122,218	75,039
Level 2 | Recurring basis | Carrying Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	78,753	34,993
Short-term restricted funds	45,062	200,339
Short-term investments	1,530,206	1,319,380
Long-term restricted funds	105,051	104,496
Long-term investments	326,047	14,661
Total	2,085,119	1,673,869
Level 2 | Recurring basis | Fair Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	78,753	34,993
Short-term restricted funds	45,062	200,339
Short-term investments	1,530,206	1,319,380
Long-term restricted funds	105,051	104,496
Long-term investments	326,047	14,661
Total	2,085,119	1,673,869
Level 2 | Commercial paper | Recurring basis | Carrying Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	70,524	9,993
Short-term investments	413,010	391,073
Long-term investments		6,967
Level 2 | Commercial paper | Recurring basis | Fair Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	70,524	9,993
Short-term investments	413,010	391,073
Long-term investments		6,967
Level 2 | Corporate securities | Recurring basis | Carrying Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	8,229
Short-term investments	986,985	848,307
Long-term investments	326,047	7,694
Level 2 | Corporate securities | Recurring basis | Fair Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	8,229
Short-term investments	986,985	848,307
Long-term investments	326,047	7,694
Level 2 | US Agency Securities | Recurring basis | Carrying Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Short-term investments	24,996
Level 2 | US Agency Securities | Recurring basis | Fair Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Short-term investments	24,996
Level 2 | U.S. Treasury bills | Recurring basis | Carrying Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Short-term restricted funds	45,062
Long-term restricted funds	1,002
Level 2 | U.S. Treasury bills | Recurring basis | Fair Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Short-term restricted funds	45,062
Long-term restricted funds	1,002
Level 2 | U.S. Treasury notes | Recurring basis | Carrying Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Short-term restricted funds		200,339
Long-term restricted funds	104,049	104,496
Level 2 | U.S. Treasury notes | Recurring basis | Fair Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Short-term restricted funds		200,339
Long-term restricted funds	104,049	104,496
Level 2 | Certificates of deposit | Recurring basis | Carrying Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents		25,000
Short-term investments	105,215	80,000
Level 2 | Certificates of deposit | Recurring basis | Fair Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents		25,000
Short-term investments	$105,215	$80,000

Property_Plant_and_Equipment_D

Property, Plant, and Equipment (Details) (USD $)	12 Months Ended			1 Months Ended	0 Months Ended	2 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2013	Dec. 20, 2011	Jul. 31, 2014	Feb. 26, 2013
Property, Plant, and Equipment
Well and development costs	$183,221,000	$92,579,000
Total proved properties	183,221,000	92,579,000
Oil and gas leasehold	762,518,000	754,894,000
Less: accumulated valuation allowance	-211,224,000	-160,913,000
Total oil and gas leasehold	551,294,000	593,981,000
Total unproved leasehold properties	1,737,758,000	1,371,804,000
Total oil and gas properties, net	1,920,979,000	1,464,383,000
Property, plant, and equipment, gross	20,359,000	16,286,000
Less: accumulated depreciation and amortization	-8,977,000	-4,394,000
Total other property and equipment	11,382,000	11,892,000
Total property, plant, and equipment, net	1,932,361,000	1,476,275,000
Depreciation and amortization	4,584,000	1,874,000	1,197,000
Unproved property acquisition costs, net of valuation allowance
Unproved property	762,518,000	754,894,000
Accumulated valuation allowance & impairment	-211,224,000	-160,913,000
Total oil and gas leasehold	551,294,000	593,981,000
Unproved	27,784,000	37,584,000	19,961,000
Gain (loss) on sale of assets	-12,000	2,993,000
Blocks 9, 20 and 21 offshore Angola
Unproved property acquisition costs, net of valuation allowance
Unproved property, net of valuation allowance	353,400,000	355,900,000
Percentage of working interest acquired	40.00%
Diaba Block offshore Gabon
Unproved property acquisition costs, net of valuation allowance
Unproved property, net of valuation allowance	2,000,000
Unproved Property Acquisition Costs Relating To Working Interest	21.25
Block 9, offshore Angola
Property, Plant, and Equipment
Expected impairment charges	2,500,000
Unproved property acquisition costs, net of valuation allowance
Percentage of working interest acquired	40.00%
Exploration well costs
Property, Plant, and Equipment
Well and development costs	51,100,000	31,600,000
Development well costs
Property, Plant, and Equipment
Well and development costs	132,100,000	61,000,000
Oil and gas properties, net
Unproved property acquisition costs, net of valuation allowance
Individual oil and gas leaseholds with carrying value less than $1 million	83,700,000	68,900,000
Upper limit of individual leasehold	1,000,000
Upper limit of unproved leasehold costs on individual properties included in group amortization	1,000,000
Carrying amount of unproved properties subject to amortization before impairment provision	83,700,000	68,900,000
Lease impairment allowance	70,500,000	87,000,000	60,200,000
Oil and gas properties, net | Mississippi Canyon Block 209
Unproved property acquisition costs, net of valuation allowance
Total consideration for the sale							5,600,000
Consideration for the sale received at closing date				1,500,000
Additional consideration for the sale receivable on commencement of operations				1,500,000
Contingent consideration for the sale to be receivable on commencement of production							2,600,000
Gain (loss) on sale of assets		3,000,000
Oil and gas properties, net | Block 20, offshore Angola
Unproved property acquisition costs, net of valuation allowance
Percentage of working interest acquired					40.00%
Consideration for the acquisition					347,100,000
Consideration payable over five years on acquisition					337,100,000
Period over which consideration is payable					5 years
Short-term and long-term contractual obligations	128,600,000
Oil and gas properties, net | Blocks 9, 20 and 21 offshore Angola
Property, Plant, and Equipment
Oil and gas leasehold	355,876,000	355,876,000
Unproved property acquisition costs, net of valuation allowance
Unproved property	355,876,000	355,876,000
Oil and gas properties, net | Diaba Block offshore Gabon
Property, Plant, and Equipment
Oil and gas leasehold	1,995,000	1,995,000
Unproved property acquisition costs, net of valuation allowance
Unproved property	1,995,000	1,995,000
Oil and gas properties, net | U.S. Gulf of Mexico
Property, Plant, and Equipment
Oil and gas leasehold	404,647,000	397,023,000
Less: accumulated valuation allowance	-208,724,000	-160,913,000
Unproved property acquisition costs, net of valuation allowance
Individual oil and gas leaseholds with carrying value greater than $1 million	320,731,000	328,128,000
Individual oil and gas leaseholds with carrying value less than $1 million	83,916,000	68,895,000
Unproved property	404,647,000	397,023,000
Accumulated valuation allowance & impairment	-208,724,000	-160,913,000
Unproved property, net of valuation allowance	195,923,000	236,110,000
Lower limit of individual leasehold	1,000,000
Ownership Interest Acquisition Aggregate Consideration						27,800,000
Lower limit of unproved leasehold costs assessed individually for impairment	1,000,000
Carrying amount of unproved properties subject to amortization before impairment provision	83,916,000	68,895,000
Oil and gas properties, net | West Africa
Property, Plant, and Equipment
Oil and gas leasehold	357,871,000	357,871,000
Less: accumulated valuation allowance	-2,500,000
Unproved property acquisition costs, net of valuation allowance
Unproved property	357,871,000	357,871,000
Accumulated valuation allowance & impairment	-2,500,000
Unproved property, net of valuation allowance	355,371,000	357,871,000
Oil and gas properties, net | Garden Banks Block 822, Mississippi Canyon Block 605 and Walker Ridge Block 232
Unproved property acquisition costs, net of valuation allowance
Consideration paid on acquisition		37,600,000
Exploration wells in process
Property, Plant, and Equipment
Total unproved leasehold properties	1,186,464,000	777,823,000
Computer equipment and software
Property, Plant, and Equipment
Estimated Useful Life	3 years
Property, plant, and equipment, gross	5,672,000	5,115,000
Office equipment and furniture
Property, Plant, and Equipment
Property, plant, and equipment, gross	2,139,000	2,132,000
Office equipment and furniture | Minimum
Property, Plant, and Equipment
Estimated Useful Life	3 years
Office equipment and furniture | Maximum
Property, Plant, and Equipment
Estimated Useful Life	5 years
Vehicles
Property, Plant, and Equipment
Estimated Useful Life	3 years
Property, plant, and equipment, gross	265,000	265,000
Leasehold improvements
Property, Plant, and Equipment
Property, plant, and equipment, gross	2,488,000	2,456,000
Leasehold improvements | Minimum
Property, Plant, and Equipment
Estimated Useful Life	3 years
Leasehold improvements | Maximum
Property, Plant, and Equipment
Estimated Useful Life	10 years
Running tools and equipment
Property, Plant, and Equipment
Estimated Useful Life	3 years
Property, plant, and equipment, gross	$9,795,000	$6,318,000

Property_Plant_and_Equipment_D1

Property, Plant, and Equipment (Details 2) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net changes in capitalized exploratory well costs (excluding any related leasehold costs)
Beginning of period	$777,823	$451,024	$178,338
Reclassification to wells, facilities, and equipment based on determination of proved reserves		-38,446
Amounts charged to expense	-165,459	-263,439	-73,918
End of period	1,186,464	777,823	451,024
Cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs)
Cumulative costs	1,186,464	777,823	451,024
Well costs capitalized for a period greater than one year after completion of drilling	775,379	399,775	194,853
Offshore Angola
Net changes in capitalized exploratory well costs (excluding any related leasehold costs)
Amounts charged to expense	101,200
Exploration well costs
Cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs)
Number of projects with exploration well costs that have been capitalized more than a year	8	3	3
Exploration well costs | Diaba Block offshore Gabon
Net changes in capitalized exploratory well costs (excluding any related leasehold costs)
Amounts charged to expense		-17,100
Exploration well costs | Offshore Angola
Net changes in capitalized exploratory well costs (excluding any related leasehold costs)
Amounts charged to expense		-126,300
U.S. Gulf of Mexico
Net changes in capitalized exploratory well costs (excluding any related leasehold costs)
Amounts charged to expense	64,300
Cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs)
Well costs capitalized for a period greater than one year after completion of drilling	208,634	186,510	89,490
U.S. Gulf of Mexico | Exploration well costs
Net changes in capitalized exploratory well costs (excluding any related leasehold costs)
Beginning of period	204,707
Additions to capitalized exploration	143,431	154,877	178,295
Amounts charged to expense		-120,000
End of period	283,885	204,707
Cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs)
Cumulative costs	283,885	204,707
U.S. Gulf of Mexico | Capitalized interest
Net changes in capitalized exploratory well costs (excluding any related leasehold costs)
Beginning of period	3,928
Additions to capitalized exploration	6,965	3,928
End of period	10,894	3,928
Cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs)
Cumulative costs	10,894	3,928
West Africa
Cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs)
Well costs capitalized for a period greater than one year after completion of drilling	566,745	213,265	105,363
West Africa | Exploration well costs
Net changes in capitalized exploratory well costs (excluding any related leasehold costs)
Beginning of period	556,917
Additions to capitalized exploration	379,461	457,608	168,309
End of period	835,171	556,917
Cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs)
Cumulative costs	835,171	556,917
West Africa | Capitalized interest
Net changes in capitalized exploratory well costs (excluding any related leasehold costs)
Beginning of period	12,271
Additions to capitalized exploration	44,243	12,271
End of period	56,514	12,271
Cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs)
Cumulative costs	$56,514	$12,271

Other_Assets_Details

Other Assets (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 17, 2012	13-May-14
Other Assets
Debt issue cost	$36,708,000	$20,983,000
Long-term portion of prepaid shorebase leases	2,244,000	3,241,000
Rig mobilization costs	14,984,000	11,153,000
Long-term accounts receivable		17,923,000
Other		437,000
Other assets	53,936,000	53,737,000
Interest rate (as a percent)	3.13%		2.63%
Blocks 9 and 21 offshore Angola
Other Assets
Long-term accounts receivables from former partner		17,900,000
Percentage of paying interest due from related parties		3.75%
2.625% convertible senior notes due 2019
Other Assets
Debt issue cost	18,500,000	21,000,000
Interest rate (as a percent)	2.63%	2.63%	2.63%	2.63%
3.125% convertible senior notes due 2024
Other Assets
Debt issue cost	$18,200,000
Interest rate (as a percent)	3.13%				3.13%

Longterm_Debt_Details

Long-term Debt (Details) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 17, 2012	Dec. 17, 2012	13-May-14
						item
Debt instrument
Interest rate (as a percent)	3.13%		2.63%
Interest paid	$56,764,000	$34,615,000
Carrying amounts of the liability components
Carrying amount of the liability components	1,928,528,000	1,035,980,000
Carrying amounts of the equity components
Fair value of the notes excluding conversion feature	2,408,000,000	1,227,000,000
Interest expense, net of capitalized amount	74,768,000	65,376,000	3,212,000
Notes
Debt instrument
Accrued interest recorded	8,000,000
Repurchase price as a percentage of principal amount of debt instrument				100.00%
Specified minimum percentage of principal amount, the holders of which may declare all principal, accrued and unpaid interest to be due and payable immediately, upon the occurrence of an Event of Default				25.00%
Percentage of principal amount, which may be declared by holders of a specified principal amount to be due and payable immediately upon occurrence of an Event of Default				100.00%
Carrying amounts of the liability components
Principal Amount	2,680,000,000	1,380,000,000
Unamortized discount	-751,472,000	-344,020,000
Carrying amount of the liability components	1,928,528,000	1,035,980,000
Carrying amounts of the equity components
Debt discount relating to value of conversion option	866,340,000	390,540,000
Debt issue costs	-20,185,000	-9,124,000
Carrying amount of the equity components	846,155,000	381,416,000
2.625% convertible senior notes due 2019
Debt instrument
Aggregate principal amount of notes issued				1,380,000,000	1,380,000,000
Interest rate (as a percent)	2.63%	2.63%	2.63%	2.63%	2.63%
Initial conversion rate of common stock					0.028023
Initial conversion price per share of common stock (in dollars per share)				35.68	$35.68
Number of underlying shares that the holder of the debt instrument would receive upon conversion				38,700,000
Effective interest rate used to amortize liability component of debt issue costs (as a percent)				8.40%	8.40%
Carrying amounts of the liability components
Principal Amount	1,380,000,000	1,380,000,000
Unamortized discount	-295,509,000	-344,020,000
Carrying amount of the liability components	1,084,491,000	1,035,980,000
Remaining term of debt	5 years
Carrying amounts of the equity components
Carrying amount of the equity components		381,400,000	381,400,000
Fair value of the notes excluding conversion feature	1,361,000,000	1,227,000,000
3.125% convertible senior notes due 2024
Debt instrument
Aggregate principal amount of notes issued						1,300,000,000
Interest rate (as a percent)	3.13%					3.13%
Initial conversion rate of common stock						0.0433604
Initial conversion price per share of common stock (in dollars per share)						$23.06
Number of underlying shares that the holder of the debt instrument would receive upon conversion						56,400,000
Number of days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be redeemable	20
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be redeemable	30 days
Minimum sale price of common stock to determine eligibility of conversion	$30
Number of business days after any five consecutive trading day period during the note measurement period	5 days
Number of consecutive trading days before five consecutive business days during the note measurement period	5 days
Convertibility of debt, trading price of debt test, percentage of closing price of stock used in calculation	98.00%
Effective interest rate used to amortize liability component of debt issue costs (as a percent)						8.97%
Carrying amounts of the liability components
Principal Amount	1,300,000,000
Unamortized discount	-455,963,000
Carrying amount of the liability components	844,037,000
Remaining term of debt	9 years 6 months
Carrying amounts of the equity components
Carrying amount of the equity components	464,700,000
Fair value of the notes excluding conversion feature	$1,047,000,000

Longterm_Debt_Details_2

Long-term Debt (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Debt instrument
Interest expense associated with accrued interest	$3,271,000	$18,529,000	$1,294,000
Interest expense associated with accretion of debt discount	68,348,000	44,789,000	1,843,000
Interest expense associated with amortization of debt issue costs	3,149,000	2,058,000	75,000
Total	74,768,000	65,376,000	3,212,000
Capitalized interest costs	58,500,000	17,700,000	0
2.625% convertible senior notes due 2019
Debt instrument
Debt Issuance Costs Allocated to Liability Component	264,300,000
3.125% convertible senior notes due 2024
Debt instrument
Debt Issuance Costs Allocated to Liability Component	$121,000,000

Contractual_Obligations_Detail

Contractual Obligations (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Contractual obligations
Short-term Contractual Obligations: Social obligation payments	$50,285,000	$49,019,000
Long-term Contractual Obligations: Social obligation payments	101,945,000	124,901,000
Block 9, offshore Angola
Contractual obligations
Short-term Contractual Obligations: Social obligation payments	560,000	150,000
Long-term Contractual Obligations: Social obligation payments	21,875,000	669,000
Block 21, offshore Angola
Contractual obligations
Short-term Contractual Obligations: Social obligation payments	1,156,000	300,000
Long-term Contractual Obligations: Social obligation payments	74,000	1,381,000
Block 20, offshore Angola
Contractual obligations
Short-term Contractual Obligations: Social obligation payments	48,569,000	48,569,000
Long-term Contractual Obligations: Social obligation payments	79,996,000	122,851,000
Payment of short-term contractual obligation	$128,600,000

Stockholders_Equity_Details

Stockholders' Equity (Details) (USD $)	0 Months Ended
	Jan. 15, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 29, 2012	Dec. 17, 2012	13-May-14
Stockholders' Equity
Common stock, shares issued		408,505,079	406,949,839		18,050,000
Common stock, par value (in dollars per share)		$0.01	$0.01		$28
Equity Based Compensation
Interest rate (as a percent)		3.13%		2.63%
2.625% convertible senior notes due 2019
Equity Based Compensation
Aggregate principal amount of notes issued						$1,380,000,000
Interest rate (as a percent)		2.63%	2.63%	2.63%		2.63%
Carrying amount of the equity components			381,400,000	381,400,000
3.125% convertible senior notes due 2024
Equity Based Compensation
Aggregate principal amount of notes issued							1,300,000,000
Interest rate (as a percent)		3.13%					3.13%
Carrying amount of the equity components		$464,700,000
Deferred Compensation Plan
Equity Based Compensation
Aggregate number of shares withheld to satisfy tax withholding obligations of employees relating to equity based compensation	9,127
Stock price of shares withheld to satisfy tax withholding obligations of employees relating to equity based compensation (in dollars per share)	$18.74

Seismic_and_Exploration_Expens2

Seismic and Exploration Expenses (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Seismic and Exploration Expenses
Seismic costs	$34,359	$63,721	$42,447
Leasehold delay rentals	7,391	6,660	6,383
Drilling rig expense and other exploration expense	43,817	3,832	12,753
Total seismic and exploration expenses	$85,567	$74,213	$61,583

Equity_Based_Compensation_Deta

Equity Based Compensation (Details) (USD $)	3 Months Ended	12 Months Ended			0 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 19, 2015	Jan. 15, 2015
Incentive Plan
Equity Based Compensation
Net new issuance	26,853
Shares available for grant under the plan		4,043,263			132,414
NED Plan
Equity Based Compensation
Shares available for grant under the plan		415,682
Restricted Stock
Restricted Shares
Non-vested shares at beginning of the period		4,334,886	4,040,825	4,599,783
Granted (in shares)		2,275,317	620,840	487,710
Vested (in shares)		-1,433,172	-239,317	-738,628
Forfeited or expired (in shares)		-2,374,242	-87,462	-308,040
Forfeited (in shares)		2,306,173
Non-vested shares at end of the period		2,802,789	4,334,886	4,040,825
Weighted Average Grant Date Fair Value Per Share
Non-vested shares at beginning of the period (in dollars per share)		$14.31	$13.05	$11.27
Granted (in dollars per share)		$14.53	$24.58	$26.01
Vested (in dollars per share)		$16.32	$17.37	$13.05
Forfeited or expired (in dollars per share)		$10.63	$20.91	$12.17
Non-vested shares at end of the period (in dollars per share)		$16.44	$14.31	$13.05
Weighted-average vesting period remaining		3 years 29 days	1 year 2 months 19 days	1 year 10 months 13 days
Unrecognized compensation		$34,066	$22,467	$23,827
Restricted Stock | Incentive Plan
Restricted Shares
Granted (in shares)					2,757,982
Restricted Stock | Non-employee directors
Weighted Average Grant Date Fair Value Per Share
Weighted average fair value of shares at grant date (in dollars per share)		$17.52	$25.40	$21.35
Restricted Stock | Three senior officers
Restricted Shares
Granted (in shares)						379,746
Non-Qualified Stock Options
Equity Based Compensation
Granted (in shares)		812,055
Weighted Average Grant Date Fair Value Per Share
Unrecognized compensation		$12,200
Non-Qualified Stock Options | Three senior officers
Equity Based Compensation
Granted (in shares)						746,268
Retainer awards | Non-employee directors | Common Stock
Weighted Average Grant Date Fair Value Per Share
Awards granted (in shares)		26,438	15,318	12,221
Restricted stock units
Restricted Shares
Non-vested shares at beginning of the period		21,624	109,275	198,838
Vested (in shares)		-21,624	-87,401	-74,537
Forfeited or expired (in shares)			-250	-15,026
Non-vested shares at end of the period			21,624	109,275
Weighted Average Grant Date Fair Value Per Share
Non-vested shares at beginning of the period (in dollars per share)		$30.50	$30.50	$12.45
Vested (in dollars per share)		$30.50	$30.50	$30.50
Forfeited or expired (in dollars per share)			$30.50	$30.50
Non-vested shares at end of the period (in dollars per share)			$30.50	$30.50
Weighted-average vesting period remaining				1 year
Restricted stock units | Minimum
Weighted Average Grant Date Fair Value Per Share
Payout percentage			0.00%
Restricted stock units | Maximum
Weighted Average Grant Date Fair Value Per Share
Payout percentage			200.00%
Restricted stock units | Non-employee directors
Weighted Average Grant Date Fair Value Per Share
Awards granted (in shares)		58,038
Awards granted as on period end (in shares)		235,801
Stock Appreciation Rights (SARs) | Incentive Plan
Restricted Shares
Granted (in shares)					1,526,835

Recovered_Sheet1

Equity based Compensation (Details 2) (Non-Qualified Stock Options, USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Equity Based Compensation
Contractual term for options granted	10 years
Assumptions used to determine the fair value of each stock option granted using the Black-Scholes-Merton option-pricing model
Expected Term in Years	5 years 6 months
Expected Volatility (as a percent)	57.27%
Expected Dividends (as a percent)	0.00%
Risk-Free Interest Rate (as a percent)	1.69%
Number of Stock Options
Outstanding at the beginning of the period (in shares)	2,338,718
Granted (in shares)	812,055
Exercised (in shares)	-3,005
Forfeited or expired (in shares)	-11,221
Outstanding at the end of the period (in shares)	3,136,547	2,338,718
Vested or expected to vest at the end of the period (in shares)	1,693,193
Exercisable at the end of the period (in shares)	1,411,271
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$20.24
Granted (in dollars per share)	$17.50
Exercised (in dollars per share)	$12.45
Forfeited or expired (in dollars per share)	$24.02
Outstanding at the end of the period (in dollars per share)	$19.52	$20.24
Vested or expected to vest at the end of the period (in dollars per share)	$20.82
Exercisable at the end of the period (in dollars per share)	$17.93
Weighted-Average Remaining Contractual Term (in years)
Outstanding at the beginning of the period	7 years 6 months 26 days	8 years
Outstanding at the end of the period	7 years 6 months 26 days	8 years
Vested or expected to vest at the end of the period	8 years 7 months 10 days
Exercisable at the end of the period	6 years 3 months 18 days
Weighted-average grant-date fair value of stock options granted (in dollars per share) using the Black-Scholes option-pricing model	$9.12	$14.08
Unrecognized compensation cost	$12,200
Period for recognition of unrecognized compensation cost	2 years 5 months 16 days
Aggregate Intrinsic Value
Exercised	$17,837
Third year
Equity Based Compensation
Vesting percentage	50.00%
Fourth year
Equity Based Compensation
Vesting percentage	50.00%

Equity_based_Compensation_Deta1

Equity based Compensation (Details 3) (USD $)	12 Months Ended			0 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 03, 2010
Equity Based Compensation
Equity-based compensation costs	$31,742	$28,754	$22,410
Non-Qualified Stock Options | Employees
Equity Based Compensation
Equity-based compensation costs	9,295	7,405	3,790
Restricted stock units
Equity Based Compensation
Vesting period		3 years
Shares authorized under the plan		397,676
Equity-based compensation costs		4,619	4,272
Restricted stock units | Employees
Equity Based Compensation
Granted during the period (in shares)				198,838
Restricted stock units | Non-employee directors
Equity Based Compensation
Granted during the period (in shares)	58,038
Restricted stock units | Minimum
Equity Based Compensation
Vesting percentage		0.00%
Multiplier to determine awards vested (as a percent)		25.00%
Restricted stock units | Maximum
Equity Based Compensation
Vesting percentage		200.00%
Multiplier to determine awards vested (as a percent)		37.50%
Restricted Stock | Employees
Equity Based Compensation
Equity-based compensation costs	20,971	15,470	13,378
Restricted Stock | Non-employee directors
Equity Based Compensation
Closing price of the entity's common stock at the date of grant (in dollars per share)	$17.52	$25.40	$21.35
Equity-based compensation costs	$1,476	$1,260	$970

Employee_Benefit_Plan_Details

Employee Benefit Plan (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2006
Employee Benefit Plan
Minimum period following date of hire after which employees become eligible to participate in the Plan				3 months
Employee contribution match in plan (as a percent)				6.00%
Expenses recorded in benefit contributions to the Plan	$1	$0.80	$0.50

Income_Taxes_Details

Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Taxes
Net deferred tax asset	$568,000,000	$461,600,000	$269,600,000
Valuation allowance	568,000,000	461,600,000	269,600,000
Current taxes:
U.S. federal	0
Foreign	0
Deferred taxes:
U.S. federal	0
Foreign	0
Income Tax Expense (Benefit)	0	0	0
U.S.:
Net income (loss) as reported	-307,025,000	-387,210,000	-229,372,000
Foreign:
Net income (loss) as reported	-203,738,000	-201,814,000	-53,627,000
Net income (loss) before income tax	($510,763,000)	($589,024,000)	($282,999,000)

Income_Taxes_Details_2

Income Taxes (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of income taxes computed at the U.S. federal statutory tax rate to the Company's income tax expense (benefit)
Income tax expense (benefit) at the federal statutory rate	($178,767,000)	($206,159,000)	($99,050,000)
State income taxes, net of federal income tax benefit	-828,000	-489,000	-512,000
Foreign income taxes	-111,151,000	-70,994,000	4,447,000
Other	9,098,000	366,000	2,678,000
Valuation allowance	281,648,000	277,276,000	92,437,000
Total	0	0	0
Reconciliation of income taxes computed at the U.S. federal statutory tax rate to the Company's income tax expense (benefit)
Income tax expense (benefit) at the federal statutory rate (as a percent)	35.00%	35.00%	35.00%
State income taxes, net of federal income tax benefit (as a percent)	0.20%	0.10%	0.20%
Foreign income taxes (as a percent)	21.80%	12.10%	-1.60%
Other (as a percent)	-1.80%	-0.10%	-0.90%
Valuation allowance (as a percent)	-55.20%	-47.10%	-32.70%
Amount of previously unrecorded foreign deferred tax assets and deferred tax liability related to convertible debt excluded from the change in deferred tax asset valuation allowance		$85,300,000

Income_Taxes_Details_3

Income Taxes (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Short-term deferred tax liabilities:
Total short-term deferred tax liabilities	$30,334,000	$17,061,000
Long-term deferred tax liabilities:
Oil and gas properties	54,461,000	22,135,000
Total long-term deferred tax liabilities	288,439,000	126,086,000
Long-term deferred tax assets:
Seismic and exploration costs	457,854,000	280,095,000
Stock-based compensation	18,092,000	20,842,000
Domestic NOL carry forwards	415,608,000	273,163,000
Foreign NOL carry forwards	38,200,000	28,633,000
Other	-43,021,000	1,976,000
Valuation allowance	-567,960,000	-461,562,000
Total long-term deferred assets	318,773,000	143,147,000
Net long-term deferred assets	30,334,000	17,061,000
Income tax expense or benefit	0	0	0
Unrecognized tax benefits	0	0
Accrued interest or penalties associated with unrecognized tax benefits	0	0
Federal
Long-term deferred tax assets:
Net operating loss carryforwards	1,200,000,000
State
Long-term deferred tax assets:
Net operating loss carryforwards	65,200,000
Foreign
Long-term deferred tax assets:
Net operating loss carryforwards	73,800,000
2.625% convertible senior notes due 2019
Short-term deferred tax liabilities:
Short-term deferred tax liabilities	18,479,000	17,061,000
Long-term deferred tax liabilities:
Long-term deferred tax liabilities	85,471,000	103,951,000
3.125% convertible senior notes due 2024
Short-term deferred tax liabilities:
Short-term deferred tax liabilities	11,855,000
Long-term deferred tax liabilities:
Long-term deferred tax liabilities	$148,507,000

Commitments_Details

Commitments (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Contractual obligation and commitments
2015	$617,666,000
2016	394,692,000
2017	221,134,000
2018	27,469,000
2019	4,378,000
Thereafter	12,849,000
Office and delay rental expense	12,800,000	6,700,000	12,100,000
Drilling Rig and Related Contracts
Contractual obligation and commitments
2015	544,559,000
2016	299,702,000
2017	208,104,000
2018	17,104,000
Operating Leases
Contractual obligation and commitments
2015	9,755,000
2016	4,801,000
2017	2,309,000
2018	2,369,000
2019	2,405,000
Thereafter	5,626,000
Lease Rentals
Contractual obligation and commitments
2015	7,353,000
2016	5,460,000
2017	5,007,000
2018	2,282,000
2019	1,973,000
Thereafter	7,223,000
Social and Work Program Payment Obligations
Contractual obligation and commitments
2015	55,999,000
2016	84,729,000
2017	5,714,000
2018	$5,714,000

Segment_Information_Details

Segment Information (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
									segment
Segment Information
Number of geographic operating segments									2
Segment Information
Operating costs and expense	$196,097	$120,961	$77,591	$47,293	$209,204	$145,663	$65,365	$112,452	$441,941	$532,684	$284,828
Operating income (loss)	-196,097	-120,961	-77,591	-47,293	-209,204	-145,663	-65,365	-112,452	-441,941	-532,684	-284,828
Other income (expense)									-68,822	-56,340	1,829
Net income (loss)	-216,564	-142,529	-94,756	-56,915	-222,119	-160,000	-78,818	-128,087	-510,763	-589,024	-282,999
Additions to Property and Equipment, net									456,086	376,519	236,430
United States
Segment Information
Operating costs and expense									238,214	329,832	231,196
Operating income (loss)									-238,214	-329,832	-231,196
Additions to Property and Equipment, net									135,449	44,124	67,068
West Africa
Segment Information
Operating costs and expense									203,727	202,852	53,632
Operating income (loss)									-203,727	-202,852	-53,632
Additions to Property and Equipment, net									$320,637	$332,395	$169,362

Related_Party_Transactions_Det

Related Party Transactions (Details) (Software licensing and consulting service agreement, Quorum, USD $)	0 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Feb. 20, 2013	Dec. 31, 2014	Dec. 31, 2013
Software licensing and consulting service agreement | Quorum
Related party transactions
Initial term to license, host and support software	3 years
Value of agreement	$1.50
Amount incurred		$1.50	$1.30

Selected_Quarterly_Financial_D2

Selected Quarterly Financial Data-Unaudited (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Selected Quarterly Financial Data Unaudited
Operating costs and expense	$196,097	$120,961	$77,591	$47,293	$209,204	$145,663	$65,365	$112,452	$441,941	$532,684	$284,828
Operating income (loss)	-196,097	-120,961	-77,591	-47,293	-209,204	-145,663	-65,365	-112,452	-441,941	-532,684	-284,828
Net income (loss)	($216,564)	($142,529)	($94,756)	($56,915)	($222,119)	($160,000)	($78,818)	($128,087)	($510,763)	($589,024)	($282,999)
Basic and diluted income (loss) per common share (in dollars per share)	($0.53)	($0.35)	($0.23)	($0.14)	($0.55)	($0.39)	($0.19)	($0.31)	($1.25)	($1.45)	($0.70)

Supplemental_Information_on_Oi2

Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Capitalized Costs Related to Oil and Gas Activities
Unproved properties	$1,948,982,000	$1,532,717,000
Accumulated valuation allowance	-211,224,000	-160,913,000
Unproved properties, net	1,737,758,000	1,371,804,000
Proved properties	183,221,000	92,579,000
Net capitalized costs	1,920,979,000	1,464,383,000
Gain (loss) recognized on sale and exchange of leasehold interests transactions	0	0
U.S. Gulf of Mexico
Capitalized Costs Related to Oil and Gas Activities
Unproved properties	699,426,000	605,658,000
Accumulated valuation allowance	-208,724,000	-160,913,000
Unproved properties, net	490,702,000	444,745,000
Proved properties	183,221,000	92,579,000
Net capitalized costs	673,923,000	537,324,000
Proceeds from sale and exchange of leasehold interests transactions	5,600,000	10,700,000
West Africa
Capitalized Costs Related to Oil and Gas Activities
Unproved properties	1,249,556,000	927,059,000
Accumulated valuation allowance	-2,500,000
Unproved properties, net	1,247,056,000	927,059,000
Net capitalized costs	$1,247,056,000	$927,059,000

Supplemental_Information_on_Oi3

Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) (Details 2) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property acquisition
Unproved	$27,784	$37,584	$19,961
Exploration
Capitalized	574,100	628,685	346,604
Expensed	85,567	74,213	61,583
Development	90,642	54,133
Total Costs Incurred	778,093	794,615	428,148
U.S. Gulf of Mexico
Property acquisition
Unproved	27,784	37,584	19,961
Exploration
Capitalized	150,396	158,806	178,295
Expensed	31,531	48,688	32,874
Development	90,642	54,133
Total Costs Incurred	300,353	299,211	231,130
West Africa
Exploration
Capitalized	423,704	469,879	168,309
Expensed	54,036	25,525	28,709
Total Costs Incurred	$477,740	$495,404	$197,018

Supplemental_Information_on_Oi4

Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) (Details 3)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
	MMBoe	MMBoe
Proved undeveloped energy reserves:
Beginning of the year	8.5
Discoveries		8.5
Revisions	0.5
End of the year	9	8.5
Period for calculating un-weighted arithmetic average of the first-day-of-the-month prices	12 months
Natural Gas (in Bcf)
Proved undeveloped reserves:
Beginning of the year	3.4
Discoveries		3.4
Revisions	0.3
End of the year	3.7	3.4
Proved undeveloped energy reserves:
Unweighted average resulting price (in dollars per Bbl or Mcf)	4.77
Natural Gas (in Bcf) | Henry Hub
Proved undeveloped energy reserves:
Unweighted arithmetic average price (in dollars per Bbl or MMbtu)	4.35
Oil and Condensate (in MMbls)
Proved undeveloped reserves:
Beginning of the year	7.9
Discoveries		7.9
Revisions	0.5
End of the year	8.4	7.9
Proved undeveloped energy reserves:
Unweighted average resulting price (in dollars per Bbl or Mcf)	95.24
Oil and Condensate (in MMbls) | Light Louisiana Sweet
Proved undeveloped energy reserves:
Unweighted arithmetic average price (in dollars per Bbl or MMbtu)	98.48

Supplemental_Information_on_Oi5

Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) (Details 4) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Future net cash flows relating to proved oil and gas reserves based on the standardized measure
Future cash inflows	$814,394	$830,287
Future production costs	-12,710	-6,400
Future development costs	-244,306	-302,278
Future income tax expense	0	0
Future net cash flows	557,378	521,609
10% annual discount for estimated timing of cash flows	-192,094	-244,976
Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Total	$365,284	$276,633

Supplemental_Information_on_Oi6

Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) (Details 5) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Information with respect to the company's standardized measure of discounted future net cash flows related to its proved natural gas reserves
Standardized measure, beginning	$276,633
Discoveries		276,633
Revisions Of Previous Estimates
Changes in prices and costs	-36,869
Changes in future development costs	49,700
Changes in quantities	17,351
Accretion of discount	27,663
Changes in timing and other	30,806
Standardized measure, ending	$365,284	$276,633