Cobalt International Energy 10-Q 5 May 15 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2015
Document and Entity Information
Entity Registrant Name	Cobalt International Energy, Inc.
Entity Central Index Key	1471261
Document Type	10-Q
Document Period End Date	31-Mar-15
Amendment Flag	FALSE
Current Fiscal Year End Date	-19
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding	414,414,019
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheets (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$354,803	$258,721
Joint interest and other receivables	29,531	59,974
Prepaid expenses and other current assets	30,367	14,497
Inventory	83,518	94,674
Short-term restricted funds	22,538	45,062
Short-term investments	1,525,072	1,530,206
Total current assets	2,045,829	2,003,134
Property, plant, and equipment:
Oil and gas properties, successful efforts method of accounting, net of accumulated depletion of $-0-	2,085,074	1,920,979
Other property and equipment, net of accumulated depreciation and amortization of $10,319 and $8,977, as of March 31, 2015 and December 31, 2014, respectively	10,103	11,382
Total property, plant, and equipment, net	2,095,177	1,932,361
Long-term restricted funds	82,419	105,051
Long-term investments	65,624	326,047
Deferred income taxes	30,995	30,334
Other assets	63,690	53,936
Total assets	4,383,734	4,450,863
Current liabilities:
Trade and other accounts payable	36,660	8,010
Accrued liabilities	216,436	214,972
Short-term contractual obligations	107,994	50,285
Deferred income taxes	30,995	30,334
Total current liabilities	392,085	303,601
Long-term debt	1,949,293	1,928,528
Long-term contractual obligations	1,381	101,945
Other long-term liabilities	2,483	2,523
Total long-term liabilities	1,953,157	2,032,996
Stockholders' Equity:
Common stock, $0.01 par value per share; 2,000,000,000 shares authorized 408,508,529 and 408,505,079 issued and outstanding as of March 31, 2015 and December 31, 2014, respectively	4,085	4,085
Additional paid-in capital	4,143,646	4,137,803
Accumulated deficit during the development stage	-2,109,239	-2,027,622
Total stockholders' equity	2,038,492	2,114,266
Total liabilities and stockholders' equity	$4,383,734	$4,450,863

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, except Share data, unless otherwise specified
Condensed 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)	$10,319	$8,977
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	408,508,529	408,505,079
Common stock, shares outstanding	408,508,529	408,505,079

Condensed_Consolidated_Stateme

Condensed Consolidated Statements of Operations (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Operating costs and expenses:
Seismic and exploration	$17,769	$8,976
Dry hole expense and impairment	19,897	13,041
General and administrative	24,249	24,169
Depreciation and amortization	1,342	1,107
Total operating costs and expenses	63,257	47,293
Operating income (loss)	-63,257	-47,293
Other income (expense):
Interest income	1,660	945
Interest expense	-20,020	-10,567
Total other income (expense)	-18,360	-9,622
Net income (loss) before income tax	-81,617	-56,915
Net income (loss)	($81,617)	($56,915)
Basic and diluted income (loss) per share (in dollars per share)	($0.20)	($0.14)
Basic and diluted weighted average common shares outstanding (in shares)	408,508,154	407,001,208

Condensed_Consolidated_Stateme1

Condensed 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, 2014	$4,085	$4,137,803	($2,027,622)	$2,114,266
Equity based compensation		5,843		5,843
Net income (loss)			-81,617	-81,617
Balance at Mar. 31, 2015	$4,085	$4,143,646	($2,109,239)	$2,038,492

Condensed_Consolidated_Stateme2

Condensed Consolidated Statements of Cash Flows (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Cash flows provided from operating activities
Net income (loss)	($81,617)	($56,915)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Depreciation and amortization	1,342	1,107
Dry hole expense and impairment of unproved properties	19,897	13,041
Equity based compensation	5,843	8,257
Amortization of premium (accretion of discount) on investments	4,800	4,230
Amortization of debt discount	19,868	12,352
Changes in operating assets and liabilities:
Joint interest and other receivables	30,443	46,223
Inventory	11,035	-4,487
Prepaid expense and other current assets	-15,870	27,348
Deferred charges and other	-9,518	5,094
Trade and other accounts payable	18,744	-116,091
Accrued liabilities and other	-22,147	-25,832
Net cash provided by (used in) operating activities	-17,180	-85,673
Cash flows from investing activities
Capital expenditures for oil and gas properties	-42,855	-42,855
Capital expenditures for other property and equipment	-63	-291
Exploration wells drilling in process	-149,733	-85,307
Change in restricted funds	-855	43,659
Proceeds from maturity of investment securities	372,350	519,205
Purchase of investment securities	-65,582	-388,797
Net cash provided by (used in) investing activities	113,262	45,614
Cash flows from financing activities
Proceeds from stock option exercises		33
Payments for common stock withheld for taxes on equity based compensation		-630
Net cash provided by (used in) financing activities		-597
Net increase (decrease) in cash and cash equivalents	96,082	-40,656
Cash and cash equivalents, beginning of period	258,721	192,460
Cash and cash equivalents, end of period	354,803	151,804
Non-Cash Disclosures
Changes in accrued capital expenditures	-8,716	29,959
Transfer of investment securities to and from restricted funds	$46,049	$42,672

Summary_of_Significant_Account

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2015
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies
	1. Summary of Significant Accounting Policies
	General
	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.
	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
	The accompanying unaudited condensed consolidated financial statements include the financial statements of Cobalt International Energy, Inc. and all of its wholly-owned subsidiaries. All significant intercompany transactions and amounts have been eliminated for all periods presented.
	The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with United States generally accepted accounting principles ("GAAP") for interim financial information and the appropriate rules and regulations of the Securities and Exchange Commission ("SEC"). Accordingly, the condensed consolidated financial statements do not include all of the information and footnote disclosures required by GAAP for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation have been included. Operating results for interim periods are not necessarily indicative of the results that may be presented for the entire year. These unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes included in the Company's Annual Report on Form 10-K for the year ended December 31, 2014.
	Recently Issued Accounting Standards
	In April 2015, the FASB amended Accounting Standard Codification Subtopic No. 835-30, Interest—Imputation of Interest (the "ASC Subtopic 835-30"). The amendments require that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The recognition and measurement guidance for debt issuance costs are not affected by the amendments. The amendments under ASC Subtopic 835-30 are effective for financial statements issued for fiscal years beginning after December 15, 2015 and interim periods within those fiscal years. However, early adoption is permitted for financial statements that have not been previously issued. The Company expects to comply with the amendments to ASC Subtopic 830-30 for its financial statements at its effective date beginning after December 15, 2015.
	Use of Estimates
	The preparation of financial statements in conformity with GAAP requires the Company to make estimates and assumptions that affect the reported amounts of assets 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 made by the Company include (i) accruals related to expenses, (ii) assumptions used in estimating fair value of equity based awards and the fair value of the liability component of the convertible senior notes and (iii) assumptions used in impairment testing. Although the Company believes these estimates are reasonable, actual results could differ from these estimates.
	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 March 31, 2015 and December 31, 2014. Income related to these securities is reported as a component of interest income in the Company's condensed consolidated statement of operations. See Note 5—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 March 31, 2015 and December 31, 2014, 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 7—Property, Plant, and Equipment and Note 9—Long-term Debt.
	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 three months ended March 31, 2015, 10,085,521 shares of non-vested restricted stock, non-vested restricted stock units, outstanding stock options, the shares underlying 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 three months ended March 31, 2014, 8,606,462 shares of non-vested restricted stock, non-vested restricted stock units, outstanding stock options and the shares underlying the 2.625% convertible senior notes due 2019 were excluded from the diluted income (loss) per share because they are anti-dilutive.

Cash_and_Cash_Equivalents

Cash and Cash Equivalents	3 Months Ended
	Mar. 31, 2015
Cash and Cash Equivalents.
Cash and Cash Equivalents
	2. Cash and Cash Equivalents
	Cash and cash equivalents consisted of the following:
			March 31,		December 31,
			2015		2014
			($ in thousands)
	Cash at banks		$	121,512	$	57,750
	Money market funds			111,310		122,218
	Held-to-maturity securities(1)			121,981		78,753
			$	354,803	$	258,721
	-1	These securities mature three months or less from the date of purchase.

Restricted_Funds

Restricted Funds	3 Months Ended
	Mar. 31, 2015
Restricted Funds
Restricted Funds
	3. Restricted Funds
	Restricted funds consisted of the following:
			March 31,		December 31,
			2015		2014
			($ in thousands)
	Short-term:
	Collateral on letters of credit for Angola		$	22,538	$	45,062
			$	22,538	$	45,062
	Long-term:
	Collateral on letters of credit for Angola		$	82,419	$	105,051
			$	82,419	$	105,051
	Total restricted funds(1)		$	104,957	$	150,113
	-1	As of March 31, 2015, $105.0 million 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 and 20 offshore Angola. As of December 31, 2014, $150.1 million 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. As of March 31, 2015 and December 31, 2014, the collateral in this account was invested in U.S. Treasury notes purchased at discounts and at premiums, respectively, resulting in a net carrying value of $105.0 million and $150.1 million, respectively. The contractual maturities of these securities are within one year.

Joint_Interest_and_Other_Recei

Joint Interest and Other Receivables	3 Months Ended
	Mar. 31, 2015
Joint Interest and Other Receivables
Joint Interest and Other Receivables
	4. 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 are usually settled within 30 days of the invoice date. As of March 31, 2015 and December 31, 2014, the balance in joint interest and other receivables consisted of the following:
		March 31,		December 31,
		2015		2014
		($ in thousands)
	Partners in the U.S. Gulf of Mexico	$	22,603	$	3,274
	Partners in West Africa		—		46,312
	Accrued interest on investment securities		6,674		7,663
	Other		254		2,725
		$	29,531	$	59,974

Investments

Investments	3 Months Ended
	Mar. 31, 2015
Investments
Investments
	5. 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 March 31, 2015 and December 31, 2014:
		March 31,		December 31,
		2015		2014
		($ in thousands)
	U.S. Treasury bills	$	46,054	$	46,064
	U.S. Treasury notes		104,957		104,049
	Corporate securities		1,152,688		1,321,261
	Commercial paper		358,728		483,534
	U.S. Agency securities		24,997		24,996
	Certificates of deposit		130,210		105,215
	Total	$	1,817,634	$	2,085,119
	The Company's condensed consolidated balance sheet included the following held-to-maturity securities:
		March 31,		December 31,
		2015		2014
		($ in thousands)
	Cash and cash equivalents	$	121,981	$	78,753
	Short-term investments		1,525,072		1,530,206
	Short-term restricted funds		22,538		45,062
	Long-term restricted funds		82,419		105,051
	Long-term investments		65,624		326,047
		$	1,817,634	$	2,085,119
	The contractual maturities of these held-to-maturity securities as of March 31, 2015 and December 31, 2014 were as follows:
		March 31, 2015				December 31, 2014
		Carrying		Estimated		Carrying		Estimated
		Value		Fair Value		Value		Fair Value
		($ in thousands)
	Within 1 year	$	1,647,053	$	1,647,053	$	1,759,072	$	1,759,072
	After 1 year		170,581		170,581		326,047		326,047
		$	1,817,634	$	1,817,634	$	2,085,119	$	2,085,119

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2015
Fair Value Measurements
Fair Value Measurements
	6. Fair Value Measurements
	The fair values of the Company's cash and cash equivalents, joint interest and other receivables, short-term 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, commercial paper, U.S. agency securities, 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.
	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)		March 31,
											2015
			($ in thousands)
	Cash and cash equivalents:
	Cash		$	121,512	$	121,512	$	—	$	—	$	121,512
	Money market funds			111,310		111,310		—		—		111,310
	Commercial paper			—		—		121,981		121,981		121,981
	Subtotal			232,822		232,822		121,981		121,981		354,803
	Short-term restricted funds:
	U.S. Treasury notes			—		—		22,538		22,538		22,538
				—		—		22,538		22,538		22,538
	Short-term investments:
	U.S. government agency securities			—		—		24,997		24,997		24,997
	U.S Treasury bills			—		—		46,054		46,054		46,054
	Corporate bonds			—		—		1,087,064		1,087,064		1,087,064
	Commercial paper			—		—		236,747		236,747		236,747
	Certificates of deposits			—		—		130,210		130,210		130,210
	Subtotal			—		—		1,525,072		1,525,072		1,525,072
	Long-term restricted funds:
	U.S. Treasury notes			—		—		82,419		82,419		82,419
	Subtotal			—		—		82,419		82,419		82,419
	Long-term investments:
	Corporate bonds			—		—		65,624		65,624		65,624
	Subtotal			—		—		65,624		65,624		65,624
	Total		$	232,822	$	232,822	$	1,817,634	$	1,817,634	$	2,050,456
			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 deposit			—		—		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
	-1	As of March 31, 2015 and December 31, 2014, the Company did not record any OTTI on these assets.

Property_Plant_and_Equipment

Property, Plant, and Equipment	3 Months Ended
	Mar. 31, 2015
Property, Plant, and Equipment
Property, Plant, and Equipment
	7. Property, Plant, and Equipment
	Property, plant, and equipment is stated at cost less accumulated depreciation/amortization and consisted of the following:
			Estimated		March 31,			December 31,
			Useful Life		2015			2014
			(Years)
					($ in thousands)
	Oil and Gas Properties:
	Proved properties:
	Well and development costs				$	229,170		$	183,221
	Total proved properties					229,170			183,221
	Unproved properties:
	Oil and gas leasehold					743,079			762,518
	Less: accumulated valuation allowance					(194,384	)		(211,224	)
						548,695			551,294
	Exploration wells in process					1,307,209			1,186,464
	Total unproved properties					1,855,904			1,737,758
	Total oil and gas properties, net					2,085,074			1,920,979
	Other Property and Equipment:
	Computer equipment and software		3			5,727			5,672
	Office equipment and furniture		3 - 5			2,140			2,139
	Vehicles		3			265			265
	Leasehold improvements		3 - 10			2,495			2,488
	Running tools and equipment		3			9,795			9,795
						20,422			20,359
	Less: accumulated depreciation and amortization					(10,319	)		(8,977	)
	Total other property and equipment, net					10,103			11,382
	Property, plant, and equipment, net				$	2,095,177		$	1,932,361
	The Company recorded $1.3 million and $1.1 million of depreciation and amortization expense for the three months ended March 31, 2015 and 2014, 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. During the quarter ended March 31, 2015, the Company assigned its 9.375% ownership interest in the Heidelberg prospect to its indirect wholly-owned subsidiary, Cobalt GOM #1, LLC ("GOM #1"). As a result, the carrying value of the costs capitalized for all the Heidelberg projects as of March 31, 2015 were transferred to GOM #1. GOM #1 was established to secure the Heidelberg assets for future debt instruments to fund the Heidelberg development project. As of March 31, 2015, the well and development costs consist of $89.6 million relating to exploration, appraisal and development well costs and $139.6 million for costs associated with field development. As of December 31, 2014, the well and development costs consist of $51.1 million relating to exploration, appraisal and development well costs and $132.1 million for costs associated with field development.
	Unproved Oil and Gas Properties
	As of March 31, 2015 and December 31, 2014, the Company has the following unproved property acquisition costs, net of valuation allowance on the consolidated balance sheets:
			March 31,			December 31,
			2015			2014
			($ in thousands)
	U.S. Gulf of Mexico:
	Individual oil and gas leaseholds with carrying value greater than $1 million		$	301,292		$	320,731
	Individual oil and gas leaseholds with carrying value less than $1 million			83,916			83,916
				385,208			404,647
	Accumulated valuation allowance & impairment			(191,884	)		(208,724	)
				193,324			195,923
	West Africa:
	Blocks 9, 20 and 21 offshore Angola(1)			355,876			355,876
	Diaba Block offshore Gabon			1,995			1,995
				357,871			357,871
	Accumulated impairment			(2,500	)		(2,500	)
				355,371			355,371
	Total oil and gas leasehold		$	548,695		$	551,294
	-1	In 2010, the Company acquired a license to explore for, develop and produce oil from Block 21 offshore Angola by executing a Risk Service Agreement ("Block 21 RSA") with Sonangol. The Block 21 RSA governs the Company's 40% working interest in and operatorship of Block 21 offshore Angola and forms the basis of the Company's exploration, development and production operations on this block. The Block 21 RSA provides for an initial exploration period of five years, which expired on March 1, 2015. The Company has applied for an extension of the initial exploration period for Block 21 to enable the Company to continue its exploration efforts, however, this extension is currently pending approval by Sonangol and the Angola Ministry of Petroleum.
	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):
			March 31,			December 31,
			2015			2014
			($ in thousands)
	Beginning of period		$	1,186,464		$	777,823
	Additions to capitalized exploration
	U.S. Gulf of Mexico:
	Exploration well costs			23,943			143,431
	Capitalized interest			3,544			6,965
	West Africa:
	Exploration well costs			96,739			379,461
	Capitalized interest			13,697			44,243
Reclassifications to wells, facilities, and equipment based on determination of proved reserves			—			—
Amounts charged to expense(1)			(17,178	)		(165,459	)
End of period		$	1,307,209		$	1,186,464
-1	The amount of $17.2 million for the three months ended March 31, 2015 represents primarily impairment charges related to the North Platte #2 appraisal well and additional charges on exploratory wells which were impaired in 2014. The North Platte #2 appraisal well was plugged and abandoned due to a seal failure in the riser connection system. The well was at a depth of 20,701 feet when the problem with the riser was detected. The Company is continuing to assess what additional impairment charges or other liabilities, including any environmental liabilities, might be incurred in future periods related to the North Platte #2 appraisal well and what costs may be recouped from the drilling contractor.
		March 31,			December 31,
		2015			2014
		($ in thousands)
Cumulative costs:
U.S. Gulf of Mexico
Exploration well costs		$	290,650		$	283,885
Capitalized interest			14,438			10,894
West Africa
Exploration well costs			930,573			835,171
Capitalized interest			71,548			56,514
		$	1,307,209		$	1,186,464
Well costs capitalized for a period greater than one year after completion of drilling (included in table above)		$	900,003		$	775,379
As of March 31, 2015, capitalized exploration well costs that have been suspended longer than one year are associated with the Company's Shenandoah, North Platte, Cameia, Bicuar, Lontra, Orca, Mavinga and Diaman discoveries. These well costs are suspended 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. The Heidelberg discovery has been sanctioned for development and the Heidelberg capitalized exploration and appraisal well costs were reclassified to development costs in 2013.

Other_Assets

Other Assets	3 Months Ended
	Mar. 31, 2015
Other Assets
Other Assets
	8. Other Assets
	As of March 31, 2015 and December 31, 2014, the balance in other assets consisted of the following:
			March 31,		December 31,
			2015		2014
			(in thousands)
	Debt issue cost(1)		$	35,822	$	36,708
	Long-term portion of prepaid shorebase leases			1,909		2,244
	Rig costs(2)			25,959		14,984
			$	63,690	$	53,936
	-1	As of March 31, 2015, the $35.8 million in debt issue costs was 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, as described in Note 9. 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 9. These debt issue costs are amortized over the life of the notes using the effective interest method.
	-2	As of March 31, 2015 and December 31, 2014, the $26.0 million and $15.0 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 is currently drilling in U.S. Gulf of Mexico. These costs are amortized over the term of the respective drilling rig contracts.

Longterm_Debt

Long-term Debt	3 Months Ended
	Mar. 31, 2015
Long-term Debt
Long-term Debt
	9. Long-term Debt
	As of March 31, 2015, 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 March 31, 2015 (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 March 31, 2015, 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:
			March 31, 2015								December 31, 2014
			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		$	(282,764	)	$	1,097,236	$	1,380,000	$	(295,509	)	$	1,084,491
	3.125% Notes			1,300,000			(447,943	)		852,057		1,300,000		(455,963	)		844,037
	Total		$	2,680,000		$	(730,707	)	$	1,949,293	$	2,680,000	$	(751,472	)	$	1,928,528
	-1	Unamortized discount will be amortized over the remaining life of the Notes which is 4.75 years for the 2.625% Notes and 9.25 years for the 3.125% Notes.
	The carrying amounts of the equity components of the Notes were as follows:
			March 31,			December 31,
			2015			2014
			($ in thousands)
	Debt discount relating to value of conversion option		$	866,340		$	866,340
	Debt issue costs			(20,185	)		(20,185	)
	Total		$	846,155		$	846,155
	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 (level 2). As of March 31, 2015 and December 31, 2014, the fair values of the Notes were as follows:
			March 31,			December 31,
			2015			2014
			($ in thousands)
	2.625% Notes		$	1,363,000		$	1,361,000
	3.125% Notes			1,086,000			1,047,000
	Total		$	2,449,000		$	2,408,000
	As of March 31, 2015, the Company had $27.0 million in accrued interest on the Notes.
	For the three months ended March 31, 2015 and 2014, the interest expense, net of capitalized amount, relating to the Notes was $20.0 million and $10.6 million, respectively.
	As of March 31, 2015 and December 31, 2014, the debt discounts associated with the 2.625% Notes and the 3.125% Notes resulted in the recognition of $234.0 million and $264.3 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	3 Months Ended
	Mar. 31, 2015
Contractual Obligations
Contractual Obligations
	10. Contractual Obligations
	The short-term and long-term contractual obligations consist of the following:
			March 31,		December 31,
			2015		2014
			($ in thousands)
	Short-term Contractual Obligations:
	Social obligation payments for Block 9, offshore Angola		$	21,875	$	560
	Social obligation payments for Block 21, offshore Angola			409		1,156
	Social obligation and bonus payments for Block 20, offshore Angola(1)			85,710		48,569
			$	107,994	$	50,285
	Long-term Contractual Obligations:
	Social and work program obligation payments for Block 9, offshore Angola		$	—	$	21,875
	Social obligation payments for Block 21, offshore Angola			1,381		74
	Social obligation and bonus payments for Block 20, offshore Angola(1)			—		79,996
			$	1,381	$	101,945
	-1	The total amount of social obligation payments for Block 20 has been capitalized.

Seismic_and_Exploration_Expens

Seismic and Exploration Expenses	3 Months Ended
	Mar. 31, 2015
Seismic and Exploration Expenses
Seismic and Exploration Expenses
	11. Seismic and Exploration Expenses
	Seismic and exploration expenses consisted of the following:
		Three Months
		Ended March 31,
		2015		2014
		($ in Thousands)
	Seismic costs	$	12,205	$	3,349
	Leasehold delay rentals		1,391		1,291
	Drilling rig and other exploration expense		4,173		4,336
		$	17,769	$	8,976

Equity_Based_Compensation

Equity Based Compensation	3 Months Ended
	Mar. 31, 2015
Equity Based Compensation
Equity Based Compensation
	12. 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, stock appreciation rights, 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 Monte Carlo pricing model. Restricted stock awards without market conditions 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.
	During the three months ended March 31, 2015, the Company granted a total of 3,169,028 shares of restricted stock and 746,268 stock options to employees which include 379,746 shares of restricted stock and 746,268 stock options with both service and market conditions granted to three senior officers under the terms of their employment agreements. During the three months ended March 31, 2015, the Company also granted 12,021 shares of common stock as retainer awards to non-employee directors who elected to be compensated by stock in lieu of cash payments.
	The Company recorded equity-based compensation expense, net of forfeitures, of $5.8 million and $8.3 million for the three months ended March 31, 2015 and 2014, respectively.
	On February 20, 2015, the Company issued a total of 1,526,835 stock appreciation rights ("SARs") under the Company's Long Term Incentive Plan (the "Plan") to the Company's officers, using the market price at the time of issuance of $8.87 per share. The SARs will vest with respect to one-third (1/3) of the underlying shares on each anniversary of the grant date over the next three years and may be settled, at the Company's discretion, by issuance of the Company's shares or by cash or by a combination of the Company's shares and cash based on the fair market value of the shares on date of exercise. The fair value of a SAR is determined using the Black-Scholes-Merton option-pricing model which at the date of grant was $4.53 per SAR. The Company accounts for the SAR awards as compensation cost and records a corresponding liability based on the fair value of the SARs at the end of each reporting period. As of March 31, 2015, the fair value of each SAR increased to $4.80, resulting in an increase in the aggregate fair value of the SARs of $0.3 million using the Black-Scholes-Merton option-pricing model. For the three months ended March 31, 2015, the Company recognized $0.3 million in compensation expense relating to the SAR awards.

Segment_Information

Segment Information	3 Months Ended
	Mar. 31, 2015
Segment Information
Segment Information
	13. Segment Information
	The Company currently has two geographic operating segments. 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 the three months ended March 31, 2015 and 2014:
			United			West			Total
			States			Africa
			($ in thousands)
	Three months ended March 31, 2015
	Operating costs and expense		$	51,741		$	11,516		$	63,257
	Operating income (loss)			(51,741	)		(11,516	)		(63,257	)
	Other income (expense)									(18,360	)
	Net income (loss)								$	(81,617	)
	Additions to Property and Equipment, net(1)		$	164,343		$	308,774		$	473,117
	Three months ended March 31, 2014
	Operating costs and expense		$	31,027		$	16,266		$	47,293
	Operating income (loss)			(31,027	)		(16,266	)		(47,293	)
	Other income (expense)									(9,622	)
	Net income (loss)								$	(56,915	)
	Additions to Property and Equipment, net(1)		$	21,376		$	122,888		$	144,264
	-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	3 Months Ended
	Mar. 31, 2015
Contingencies
Contingencies
	14. 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	3 Months Ended
	Mar. 31, 2015
Other Matters
Other Matters
	15. 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.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2015
Summary of Significant Accounting Policies
Basis of Presentation
	Basis of Presentation
	The accompanying unaudited condensed consolidated financial statements include the financial statements of Cobalt International Energy, Inc. and all of its wholly-owned subsidiaries. All significant intercompany transactions and amounts have been eliminated for all periods presented.
	The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with United States generally accepted accounting principles ("GAAP") for interim financial information and the appropriate rules and regulations of the Securities and Exchange Commission ("SEC"). Accordingly, the condensed consolidated financial statements do not include all of the information and footnote disclosures required by GAAP for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation have been included. Operating results for interim periods are not necessarily indicative of the results that may be presented for the entire year. These unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes included in the Company's Annual Report on Form 10-K for the year ended December 31, 2014.
Recently Issued Accounting Standards
	Recently Issued Accounting Standards
	In April 2015, the FASB amended Accounting Standard Codification Subtopic No. 835-30, Interest—Imputation of Interest (the "ASC Subtopic 835-30"). The amendments require that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The recognition and measurement guidance for debt issuance costs are not affected by the amendments. The amendments under ASC Subtopic 835-30 are effective for financial statements issued for fiscal years beginning after December 15, 2015 and interim periods within those fiscal years. However, early adoption is permitted for financial statements that have not been previously issued. The Company expects to comply with the amendments to ASC Subtopic 830-30 for its financial statements at its effective date beginning after December 15, 2015.
Use of Estimates
	Use of Estimates
	The preparation of financial statements in conformity with GAAP requires the Company to make estimates and assumptions that affect the reported amounts of assets 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 made by the Company include (i) accruals related to expenses, (ii) assumptions used in estimating fair value of equity based awards and the fair value of the liability component of the convertible senior notes and (iii) assumptions used in impairment testing. Although the Company believes these estimates are reasonable, actual results could differ from these estimates.
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 March 31, 2015 and December 31, 2014. Income related to these securities is reported as a component of interest income in the Company's condensed consolidated statement of operations. See Note 5—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 March 31, 2015 and December 31, 2014, 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 7—Property, Plant, and Equipment and Note 9—Long-term Debt.
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 three months ended March 31, 2015, 10,085,521 shares of non-vested restricted stock, non-vested restricted stock units, outstanding stock options, the shares underlying 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 three months ended March 31, 2014, 8,606,462 shares of non-vested restricted stock, non-vested restricted stock units, outstanding stock options and the shares underlying the 2.625% convertible senior notes due 2019 were excluded from the diluted income (loss) per share because they are anti-dilutive.

Cash_and_Cash_Equivalents_Tabl

Cash and Cash Equivalents (Tables)	3 Months Ended
	Mar. 31, 2015
Cash and Cash Equivalents.
Cash and cash equivalents
			March 31,		December 31,
			2015		2014
			($ in thousands)
	Cash at banks		$	121,512	$	57,750
	Money market funds			111,310		122,218
	Held-to-maturity securities(1)			121,981		78,753
			$	354,803	$	258,721
	-1	These securities mature three months or less from the date of purchase.

Restricted_Funds_Tables

Restricted Funds (Tables)	3 Months Ended
	Mar. 31, 2015
Restricted Funds
Schedule of restricted funds
			March 31,		December 31,
			2015		2014
			($ in thousands)
	Short-term:
	Collateral on letters of credit for Angola		$	22,538	$	45,062
			$	22,538	$	45,062
	Long-term:
	Collateral on letters of credit for Angola		$	82,419	$	105,051
			$	82,419	$	105,051
	Total restricted funds(1)		$	104,957	$	150,113
	-1	As of March 31, 2015, $105.0 million 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 and 20 offshore Angola. As of December 31, 2014, $150.1 million 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. As of March 31, 2015 and December 31, 2014, the collateral in this account was invested in U.S. Treasury notes purchased at discounts and at premiums, respectively, resulting in a net carrying value of $105.0 million and $150.1 million, respectively. The contractual maturities of these securities are within one year.

Joint_Interest_and_Other_Recei1

Joint Interest and Other Receivables (Tables)	3 Months Ended
	Mar. 31, 2015
Joint Interest and Other Receivables
Schedule of joint interest and other receivables
		March 31,		December 31,
		2015		2014
		($ in thousands)
	Partners in the U.S. Gulf of Mexico	$	22,603	$	3,274
	Partners in West Africa		—		46,312
	Accrued interest on investment securities		6,674		7,663
	Other		254		2,725
		$	29,531	$	59,974

Investments_Tables

Investments (Tables)	3 Months Ended
	Mar. 31, 2015
Investments
Schedule of fair value of held-to-maturity securities recorded at amortized cost
		March 31,		December 31,
		2015		2014
		($ in thousands)
	U.S. Treasury bills	$	46,054	$	46,064
	U.S. Treasury notes		104,957		104,049
	Corporate securities		1,152,688		1,321,261
	Commercial paper		358,728		483,534
	U.S. Agency securities		24,997		24,996
	Certificates of deposit		130,210		105,215
	Total	$	1,817,634	$	2,085,119
Schedule of held-to-maturity securities included in the company's condensed consolidated balance sheet
		March 31,		December 31,
		2015		2014
		($ in thousands)
	Cash and cash equivalents	$	121,981	$	78,753
	Short-term investments		1,525,072		1,530,206
	Short-term restricted funds		22,538		45,062
	Long-term restricted funds		82,419		105,051
	Long-term investments		65,624		326,047
		$	1,817,634	$	2,085,119
Schedule of contractual maturities of held-to-maturity securities
		March 31, 2015				December 31, 2014
		Carrying		Estimated		Carrying		Estimated
		Value		Fair Value		Value		Fair Value
		($ in thousands)
	Within 1 year	$	1,647,053	$	1,647,053	$	1,759,072	$	1,759,072
	After 1 year		170,581		170,581		326,047		326,047
		$	1,817,634	$	1,817,634	$	2,085,119	$	2,085,119

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2015
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)		March 31,
											2015
			($ in thousands)
	Cash and cash equivalents:
	Cash		$	121,512	$	121,512	$	—	$	—	$	121,512
	Money market funds			111,310		111,310		—		—		111,310
	Commercial paper			—		—		121,981		121,981		121,981
	Subtotal			232,822		232,822		121,981		121,981		354,803
	Short-term restricted funds:
	U.S. Treasury notes			—		—		22,538		22,538		22,538
				—		—		22,538		22,538		22,538
	Short-term investments:
	U.S. government agency securities			—		—		24,997		24,997		24,997
	U.S Treasury bills			—		—		46,054		46,054		46,054
	Corporate bonds			—		—		1,087,064		1,087,064		1,087,064
	Commercial paper			—		—		236,747		236,747		236,747
	Certificates of deposits			—		—		130,210		130,210		130,210
	Subtotal			—		—		1,525,072		1,525,072		1,525,072
	Long-term restricted funds:
	U.S. Treasury notes			—		—		82,419		82,419		82,419
	Subtotal			—		—		82,419		82,419		82,419
	Long-term investments:
	Corporate bonds			—		—		65,624		65,624		65,624
	Subtotal			—		—		65,624		65,624		65,624
	Total		$	232,822	$	232,822	$	1,817,634	$	1,817,634	$	2,050,456
			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 deposit			—		—		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
	-1	As of March 31, 2015 and December 31, 2014, the Company did not record any OTTI on these assets.

Property_Plant_and_Equipment_T

Property, Plant, and Equipment (Tables)	3 Months Ended
	Mar. 31, 2015
Property, Plant, and Equipment
Schedule of Property, Plant, and Equipment
			Estimated		March 31,			December 31,
			Useful Life		2015			2014
			(Years)
					($ in thousands)
	Oil and Gas Properties:
	Proved properties:
	Well and development costs				$	229,170		$	183,221
	Total proved properties					229,170			183,221
	Unproved properties:
	Oil and gas leasehold					743,079			762,518
	Less: accumulated valuation allowance					(194,384	)		(211,224	)
						548,695			551,294
	Exploration wells in process					1,307,209			1,186,464
	Total unproved properties					1,855,904			1,737,758
	Total oil and gas properties, net					2,085,074			1,920,979
	Other Property and Equipment:
	Computer equipment and software		3			5,727			5,672
	Office equipment and furniture		3 - 5			2,140			2,139
	Vehicles		3			265			265
	Leasehold improvements		3 - 10			2,495			2,488
	Running tools and equipment		3			9,795			9,795
						20,422			20,359
	Less: accumulated depreciation and amortization					(10,319	)		(8,977	)
	Total other property and equipment, net					10,103			11,382
	Property, plant, and equipment, net				$	2,095,177		$	1,932,361
Schedule of unproved property acquisition costs, net of valuation allowance
			March 31,			December 31,
			2015			2014
			($ in thousands)
	U.S. Gulf of Mexico:
	Individual oil and gas leaseholds with carrying value greater than $1 million		$	301,292		$	320,731
	Individual oil and gas leaseholds with carrying value less than $1 million			83,916			83,916
				385,208			404,647
	Accumulated valuation allowance & impairment			(191,884	)		(208,724	)
				193,324			195,923
	West Africa:
	Blocks 9, 20 and 21 offshore Angola(1)			355,876			355,876
	Diaba Block offshore Gabon			1,995			1,995
				357,871			357,871
	Accumulated impairment			(2,500	)		(2,500	)
				355,371			355,371
	Total oil and gas leasehold		$	548,695		$	551,294
	-1	In 2010, the Company acquired a license to explore for, develop and produce oil from Block 21 offshore Angola by executing a Risk Service Agreement ("Block 21 RSA") with Sonangol. The Block 21 RSA governs the Company's 40% working interest in and operatorship of Block 21 offshore Angola and forms the basis of the Company's exploration, development and production operations on this block. The Block 21 RSA provides for an initial exploration period of five years, which expired on March 1, 2015. The Company has applied for an extension of the initial exploration period for Block 21 to enable the Company to continue its exploration efforts, however, this extension is currently pending approval by Sonangol and the Angola Ministry of Petroleum.
Schedule of net changes in capitalized exploration well costs
			March 31,			December 31,
			2015			2014
			($ in thousands)
	Beginning of period		$	1,186,464		$	777,823
	Additions to capitalized exploration
	U.S. Gulf of Mexico:
	Exploration well costs			23,943			143,431
	Capitalized interest			3,544			6,965
	West Africa:
	Exploration well costs			96,739			379,461
	Capitalized interest			13,697			44,243
	Reclassifications to wells, facilities, and equipment based on determination of proved reserves			—			—
	Amounts charged to expense(1)			(17,178	)		(165,459	)
	End of period		$	1,307,209		$	1,186,464
	-1	The amount of $17.2 million for the three months ended March 31, 2015 represents primarily impairment charges related to the North Platte #2 appraisal well and additional charges on exploratory wells which were impaired in 2014. The North Platte #2 appraisal well was plugged and abandoned due to a seal failure in the riser connection system. The well was at a depth of 20,701 feet when the problem with the riser was detected. The Company is continuing to assess what additional impairment charges or other liabilities, including any environmental liabilities, might be incurred in future periods related to the North Platte #2 appraisal well and what costs may be recouped from the drilling contractor.
Schedule of cumulative costs of capitalized exploration well costs
			March 31,			December 31,
			2015			2014
			($ in thousands)
	Cumulative costs:
	U.S. Gulf of Mexico
	Exploration well costs		$	290,650		$	283,885
	Capitalized interest			14,438			10,894
	West Africa
	Exploration well costs			930,573			835,171
	Capitalized interest			71,548			56,514
			$	1,307,209		$	1,186,464
	Well costs capitalized for a period greater than one year after completion of drilling (included in table above)		$	900,003		$	775,379

Other_Assets_Tables

Other Assets (Tables)	3 Months Ended
	Mar. 31, 2015
Other Assets
Schedule of other assets
			March 31,		December 31,
			2015		2014
			(in thousands)
	Debt issue cost(1)		$	35,822	$	36,708
	Long-term portion of prepaid shorebase leases			1,909		2,244
	Rig costs(2)			25,959		14,984
			$	63,690	$	53,936
	-1	As of March 31, 2015, the $35.8 million in debt issue costs was 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, as described in Note 9. 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 9. These debt issue costs are amortized over the life of the notes using the effective interest method.
	-2	As of March 31, 2015 and December 31, 2014, the $26.0 million and $15.0 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 is currently drilling in U.S. Gulf of Mexico. These costs are amortized over the term of the respective drilling rig contracts.

Longterm_Debt_Tables

Long-term Debt (Tables)	3 Months Ended
	Mar. 31, 2015
Long-term Debt
Schedule of the carrying amounts of the liability components of the Notes
			March 31, 2015								December 31, 2014
			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		$	(282,764	)	$	1,097,236	$	1,380,000	$	(295,509	)	$	1,084,491
	3.125% Notes			1,300,000			(447,943	)		852,057		1,300,000		(455,963	)		844,037
	Total		$	2,680,000		$	(730,707	)	$	1,949,293	$	2,680,000	$	(751,472	)	$	1,928,528
	-1	Unamortized discount will be amortized over the remaining life of the Notes which is 4.75 years for the 2.625% Notes and 9.25 years for the 3.125% Notes.
Schedule of carrying amounts of the equity components of the Notes
			March 31,			December 31,
			2015			2014
			($ in thousands)
	Debt discount relating to value of conversion option		$	866,340		$	866,340
	Debt issue costs			(20,185	)		(20,185	)
	Total		$	846,155		$	846,155
Schedule of the fair value of the Notes excluding the conversion feature
			March 31,			December 31,
			2015			2014
			($ in thousands)
	2.625% Notes		$	1,363,000		$	1,361,000
	3.125% Notes			1,086,000			1,047,000
	Total		$	2,449,000		$	2,408,000

Contractual_Obligations_Tables

Contractual Obligations (Tables)	3 Months Ended
	Mar. 31, 2015
Contractual Obligations
Summary of components of short-term and long-term contractual obligations
			March 31,		December 31,
			2015		2014
			($ in thousands)
	Short-term Contractual Obligations:
	Social obligation payments for Block 9, offshore Angola		$	21,875	$	560
	Social obligation payments for Block 21, offshore Angola			409		1,156
	Social obligation and bonus payments for Block 20, offshore Angola(1)			85,710		48,569
			$	107,994	$	50,285
	Long-term Contractual Obligations:
	Social and work program obligation payments for Block 9, offshore Angola		$	—	$	21,875
	Social obligation payments for Block 21, offshore Angola			1,381		74
	Social obligation and bonus payments for Block 20, offshore Angola(1)			—		79,996
			$	1,381	$	101,945
	-1	The total amount of social obligation payments for Block 20 has been capitalized.

Seismic_and_Exploration_Expens1

Seismic and Exploration Expenses (Tables)	3 Months Ended
	Mar. 31, 2015
Seismic and Exploration Expenses
Schedule of seismic and exploration expenses
		Three Months
		Ended March 31,
		2015		2014
		($ in Thousands)
	Seismic costs	$	12,205	$	3,349
	Leasehold delay rentals		1,391		1,291
	Drilling rig and other exploration expense		4,173		4,336
		$	17,769	$	8,976

Segment_Information_Tables

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2015
Segment Information
Schedule of segment information by geographic operating segment
			United			West			Total
			States			Africa
			($ in thousands)
	Three months ended March 31, 2015
	Operating costs and expense		$	51,741		$	11,516		$	63,257
	Operating income (loss)			(51,741	)		(11,516	)		(63,257	)
	Other income (expense)									(18,360	)
	Net income (loss)								$	(81,617	)
	Additions to Property and Equipment, net(1)		$	164,343		$	308,774		$	473,117
	Three months ended March 31, 2014
	Operating costs and expense		$	31,027		$	16,266		$	47,293
	Operating income (loss)			(31,027	)		(16,266	)		(47,293	)
	Other income (expense)									(9,622	)
	Net income (loss)								$	(56,915	)
	Additions to Property and Equipment, net(1)		$	21,376		$	122,888		$	144,264
	-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.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 17, 2012	13-May-14
Investments
OTTI in debt securities	$0		$0
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	10,085,521	8,606,462
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%		3.13%

Cash_and_Cash_Equivalents_Deta

Cash and Cash Equivalents (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Cash and Cash Equivalents.
Cash at banks	$121,512	$57,750
Money market funds	111,310	122,218
Held-to-maturity securities	121,981	78,753
Total	$354,803	$258,721	$151,804	$192,460

Restricted_Funds_Details

Restricted Funds (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Restricted Funds
Short-term restricted funds	$22,538,000	$45,062,000
Long-term restricted funds	82,419,000	105,051,000
Collateral on letters of credit for Angola
Restricted Funds
Short-term restricted funds	22,538,000	45,062,000
Long-term restricted funds	82,419,000	105,051,000
Collateral held	104,957,000	150,113,000
Maturity period of investments	1 year
Collateral on letters of credit for Angola - block 9 and 20 | U.S. Treasury notes
Restricted Funds
Net carrying value of investments invested through the funds	105,000,000
Collateral on letters of credit for Angola - block 9, 20 and 21 | U.S. Treasury notes
Restricted Funds
Net carrying value of investments invested through the funds		$150,100,000

Joint_Interest_and_Other_Recei2

Joint Interest and Other Receivables (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Joint Interest and Other Receivables
Settlement period for bills under operating agreements	30 days
Joint Interest Receivables
Accrued interest on investment securities	$6,674	$7,663
Other	254	2,725
Total	29,531	59,974
Partners in the U.S. Gulf of Mexico
Joint Interest Receivables
Receivable attributable to joint interest partners	22,603	3,274
Partners in West Africa
Joint Interest Receivables
Receivable attributable to joint interest partners		$46,312

Investments_Details

Investments (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Investments
Fair market value	$1,817,634	$2,085,119
Held-to-maturities, Carrying value
Within 1 year	1,647,053	1,759,072
After 1 year	170,581	326,047
Total	1,817,634	2,085,119
Held-to-maturity securities, Estimated fair value
Within 1 year	1,647,053	1,759,072
After 1 year	170,581	326,047
Total	1,817,634	2,085,119
Cash and cash equivalents
Investments
Fair market value	121,981	78,753
Held-to-maturity securities, Estimated fair value
Total	121,981	78,753
Short-term investments
Investments
Fair market value	1,525,072	1,530,206
Held-to-maturity securities, Estimated fair value
Total	1,525,072	1,530,206
Short-term restricted funds
Investments
Fair market value	22,538	45,062
Held-to-maturity securities, Estimated fair value
Total	22,538	45,062
Long-term restricted funds
Investments
Fair market value	82,419	105,051
Held-to-maturity securities, Estimated fair value
Total	82,419	105,051
Long-term investments
Investments
Fair market value	65,624	326,047
Held-to-maturity securities, Estimated fair value
Total	65,624	326,047
U.S. Treasury bills.
Investments
Fair market value	46,054	46,064
Held-to-maturity securities, Estimated fair value
Total	46,054	46,064
U.S. Treasury notes
Investments
Fair market value	104,957	104,049
Held-to-maturity securities, Estimated fair value
Total	104,957	104,049
Corporate securities
Investments
Fair market value	1,152,688	1,321,261
Held-to-maturity securities, Estimated fair value
Total	1,152,688	1,321,261
Commercial paper
Investments
Fair market value	358,728	483,534
Held-to-maturity securities, Estimated fair value
Total	358,728	483,534
U.S. Agency Securities
Investments
Fair market value	24,997	24,996
Held-to-maturity securities, Estimated fair value
Total	24,997	24,996
Certificates of deposit
Investments
Fair market value	130,210	105,215
Held-to-maturity securities, Estimated fair value
Total	$130,210	$105,215

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	$354,803	$258,721	$151,804	$192,460
Short-term restricted funds	22,538	45,062
Short-term investments	1,525,072	1,530,206
Long-term restricted funds	82,419	105,051
Long-term investments	65,624	326,047
Total	2,050,456	2,265,087
Cash. | Recurring basis
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	121,512	57,750
Money market funds | Recurring basis
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	111,310	122,218
Commercial paper | Recurring basis
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	121,981	70,524
Short-term investments	236,747	413,010
U.S. Agency Securities | Recurring basis
Significant financial instruments as categorized by the fair value measurement hierarchy
Short-term investments	24,997	24,996
U.S. Treasury bills | Recurring basis
Significant financial instruments as categorized by the fair value measurement hierarchy
Short-term restricted funds		45,062
Short-term investments	46,054
Long-term restricted funds		1,002
U.S. Treasury notes
Significant financial instruments as categorized by the fair value measurement hierarchy
Short-term restricted funds	22,538
U.S. Treasury notes | Recurring basis
Significant financial instruments as categorized by the fair value measurement hierarchy
Long-term restricted funds	82,419
Long-term investments		104,049
Corporate securities | Recurring basis
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents		8,229
Short-term investments	1,087,064	986,985
Long-term investments	65,624	326,047
Certificates of deposit | Recurring basis
Significant financial instruments as categorized by the fair value measurement hierarchy
Short-term investments	130,210	105,215
Level 1 | Recurring basis | Carrying Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	232,822	179,968
Total	232,822	179,968
Level 1 | Recurring basis | Fair Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	232,822	179,968
Total	232,822	179,968
Level 1 | Cash. | Recurring basis | Carrying Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	121,512	57,750
Level 1 | Cash. | Recurring basis | Fair Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	121,512	57,750
Level 1 | Money market funds | Recurring basis | Carrying Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	111,310	122,218
Level 1 | Money market funds | Recurring basis | Fair Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	111,310	122,218
Level 2 | Recurring basis | Carrying Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	121,981	78,753
Short-term restricted funds	22,538	45,062
Short-term investments	1,525,072	1,530,206
Long-term restricted funds	82,419	105,051
Long-term investments	65,624	326,047
Total	1,817,634	2,085,119
Level 2 | Recurring basis | Fair Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	121,981	78,753
Short-term restricted funds	22,538	45,062
Short-term investments	1,525,072	1,530,206
Long-term restricted funds	82,419	105,051
Long-term investments	65,624	326,047
Total	1,817,634	2,085,119
Level 2 | Commercial paper | Recurring basis | Carrying Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	121,981	70,524
Short-term investments	236,747	413,010
Level 2 | Commercial paper | Recurring basis | Fair Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Cash and cash equivalents	121,981	70,524
Short-term investments	236,747	413,010
Level 2 | U.S. Agency Securities | Recurring basis | Carrying Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Short-term investments	24,997	24,996
Level 2 | U.S. Agency Securities | Recurring basis | Fair Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Short-term investments	24,997	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
Short-term investments	46,054
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
Short-term investments	46,054
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	22,538
Long-term restricted funds	82,419
Long-term investments		104,049
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	22,538
Long-term restricted funds	82,419
Long-term investments		104,049
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	1,087,064	986,985
Long-term investments	65,624	326,047
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	1,087,064	986,985
Long-term investments	65,624	326,047
Level 2 | Certificates of deposit | Recurring basis | Carrying Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Short-term investments	130,210	105,215
Level 2 | Certificates of deposit | Recurring basis | Fair Value
Significant financial instruments as categorized by the fair value measurement hierarchy
Short-term investments	$130,210	$105,215

Property_Plant_and_Equipment_D

Property, Plant, and Equipment (Details) (USD $)	3 Months Ended		0 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 01, 2015	Dec. 31, 2014
Property, Plant, and Equipment
Well and development costs	$229,170,000			$183,221,000
Total proved properties	229,170,000			183,221,000
Oil and gas leasehold	743,079,000			762,518,000
Less: accumulated valuation allowance	-194,384,000			-211,224,000
Total oil and gas leasehold	548,695,000			551,294,000
Total unproved properties	1,855,904,000			1,737,758,000
Total oil and gas properties, net	2,085,074,000			1,920,979,000
Property, plant, and equipment, gross	20,422,000			20,359,000
Less: accumulated depreciation and amortization	-10,319,000			-8,977,000
Total other property and equipment	10,103,000			11,382,000
Total property, plant, and equipment, net	2,095,177,000			1,932,361,000
Depreciation and amortization	1,342,000	1,107,000
Unproved property acquisition costs, net of valuation allowance
Unproved property	743,079,000			762,518,000
Accumulated valuation allowance & impairment	-194,384,000			-211,224,000
Total oil and gas leasehold	548,695,000			551,294,000
Percentage of working interest acquired	9.38%
Development well costs
Property, Plant, and Equipment
Well and development costs	139,600,000			132,100,000
Exploration wells in process
Property, Plant, and Equipment
Total unproved properties	1,307,209,000			1,186,464,000
Exploration wells in process | Exploration well costs
Property, Plant, and Equipment
Well and development costs	89,600,000			51,100,000
Computer equipment and software
Property, Plant, and Equipment
Estimated Useful Life	3 years
Property, plant, and equipment, gross	5,727,000			5,672,000
Office equipment and furniture
Property, Plant, and Equipment
Property, plant, and equipment, gross	2,140,000			2,139,000
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	2,495,000			2,488,000
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			9,795,000
Oil and gas properties, net
Property, Plant, and Equipment
Total oil and gas leasehold	548,695,000			551,294,000
Unproved property acquisition costs, net of valuation allowance
Total oil and gas leasehold	548,695,000			551,294,000
Oil and gas properties, net | U.S. Gulf of Mexico
Property, Plant, and Equipment
Oil and gas leasehold	385,208,000			404,647,000
Less: accumulated valuation allowance	-191,884,000			-208,724,000
Unproved property acquisition costs, net of valuation allowance
Individual oil and gas leaseholds with carrying value greater than $1 million	301,292,000			320,731,000
Individual oil and gas leaseholds with carrying value less than $1 million	83,916,000			83,916,000
Unproved property	385,208,000			404,647,000
Accumulated valuation allowance & impairment	-191,884,000			-208,724,000
Unproved property, net of valuation allowance	193,324,000			195,923,000
Upper limit of individual leasehold	1,000,000			1,000,000
Lower limit of individual leasehold	1,000,000			1,000,000
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			-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			-2,500,000
Unproved property, net of valuation allowance	355,371,000			355,371,000
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 | Block 21, offshore Angola
Unproved property acquisition costs, net of valuation allowance
Percentage of working interest acquired	40.00%
Period over which consideration is payable			5 years

Property_Plant_and_Equipment_D1

Property, Plant, and Equipment (Details 2) (USD $)	3 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
	ft
Capitalized Exploratory Well Costs
Period to determine an exploration well has commercially sufficient quantity of proved reserved	1 year
Net changes in capitalized exploratory well costs (excluding any related leasehold costs)
Beginning of period	$1,186,464	$777,823
Amounts charged to expense	-17,178	-165,459
End of period	1,307,209	1,186,464
Cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs)
Cumulative costs	1,307,209	1,186,464
Well costs capitalized for a period greater than one year after completion of drilling	900,003	775,379
Number of feet	20,701
U.S. Gulf of Mexico | Exploration well costs
Net changes in capitalized exploratory well costs (excluding any related leasehold costs)
Beginning of period	283,885
Additions to capitalized exploration	23,943	143,431
End of period	290,650	283,885
Cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs)
Cumulative costs	290,650	283,885
U.S. Gulf of Mexico | Capitalized interest
Net changes in capitalized exploratory well costs (excluding any related leasehold costs)
Beginning of period	10,894
Additions to capitalized exploration	3,544	6,965
End of period	14,438	10,894
Cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs)
Cumulative costs	14,438	10,894
West Africa | Exploration well costs
Net changes in capitalized exploratory well costs (excluding any related leasehold costs)
Beginning of period	835,171
Additions to capitalized exploration	96,739	379,461
End of period	930,573	835,171
Cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs)
Cumulative costs	930,573	835,171
West Africa | Capitalized interest
Net changes in capitalized exploratory well costs (excluding any related leasehold costs)
Beginning of period	56,514
Additions to capitalized exploration	13,697	44,243
End of period	71,548	56,514
Cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs)
Cumulative costs	$71,548	$56,514

Other_Assets_Details

Other Assets (Details) (USD $)	3 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 17, 2012	13-May-14
Other Assets
Debt issue cost	$35,822	$36,708
Long-term portion of prepaid shorebase leases	1,909	2,244
Rig costs	25,959	14,984
Other assets	63,690	53,936
2.625% convertible senior notes due 2019
Other Assets
Debt issue cost		18,500
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
Interest rate (as a percent)	3.13%	3.13%			3.13%

Longterm_Debt_Details

Long-term Debt (Details) (USD $)	0 Months Ended	3 Months Ended		12 Months Ended	0 Months Ended
	Dec. 17, 2012	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	13-May-14
					item
Carrying amounts of the liability components
Principal Amount		$2,680,000,000		$2,680,000,000
Unamortized discount		-730,707,000		-751,472,000
Carrying amount of the liability components		1,949,293,000		1,928,528,000
Carrying amounts of the equity components
Fair value of the notes excluding conversion feature		2,449,000,000		2,408,000,000
Notes
Debt instrument
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%
Accrued interest recorded		27,000,000
Capitalized interest costs		20,000,000	10,600,000
Debt issue cost allocated to the liability component		234,000,000		264,300,000
Carrying amounts of the equity components
Debt discount relating to value of conversion option		866,340,000		866,340,000
Debt issue costs		-20,185,000		-20,185,000
Total		846,155,000		846,155,000
2.625% convertible senior notes due 2019
Debt instrument
Aggregate principal amount of notes issued	1,380,000,000
Interest rate (as a percent)	2.63%	2.63%	2.63%	2.63%
Initial conversion rate of common stock	28.023
Initial conversion price per share of common stock (in dollars per share)	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%
Carrying amounts of the liability components
Principal Amount		1,380,000,000		1,380,000,000
Unamortized discount		-282,764,000		-295,509,000
Carrying amount of the liability components		1,097,236,000		1,084,491,000
Remaining term of debt		4 years 9 months
Carrying amounts of the equity components
Fair value of the notes excluding conversion feature		1,363,000,000		1,361,000,000
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%	3.13%
Initial conversion rate of common stock					43.3604
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		1,300,000,000
Unamortized discount		-447,943,000		-455,963,000
Carrying amount of the liability components		852,057,000		844,037,000
Remaining term of debt		9 years 3 months
Carrying amounts of the equity components
Fair value of the notes excluding conversion feature		$1,086,000,000		$1,047,000,000

Contractual_Obligations_Detail

Contractual Obligations (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Contractual obligations
Short-term Contractual Obligations: Social obligation payments	$107,994	$50,285
Long-term Contractual Obligations: Social obligation payments	1,381	101,945
Block 9, offshore Angola
Contractual obligations
Short-term Contractual Obligations: Social obligation payments	21,875	560
Long-term Contractual Obligations: Social obligation payments		21,875
Block 21, offshore Angola
Contractual obligations
Short-term Contractual Obligations: Social obligation payments	409	1,156
Long-term Contractual Obligations: Social obligation payments	1,381	74
Block 20, offshore Angola
Contractual obligations
Short-term Contractual Obligations: Social obligation payments	85,710	48,569
Long-term Contractual Obligations: Social obligation payments		$79,996

Seismic_and_Exploration_Expens2

Seismic and Exploration Expenses (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Seismic and Exploration Expenses
Seismic costs	$12,205	$3,349
Leasehold delay rentals	1,391	1,291
Drilling rig and other exploration expense	4,173	4,336
Total seismic and exploration expenses	$17,769	$8,976

Equity_Based_Compensation_Deta

Equity Based Compensation (Details) (USD $)	3 Months Ended		0 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Feb. 20, 2015
Number of Stock Options
Equity based compensation expense, net of forfeitures recognized	$5,843,000	$8,257,000
Restricted Stock
Restricted Shares
Granted (in shares)	3,169,028
Restricted Stock | Three senior officers
Restricted Shares
Granted (in shares)	379,746
Retainer awards | Non-employee directors | Common Stock
Restricted Shares
Awards granted (in shares)	12,021
Non-Qualified Stock Options
Number of Stock Options
Granted (in shares)	746,268
Non-Qualified Stock Options | Three senior officers
Number of Stock Options
Granted (in shares)	746,268
Stock appreciation rights ("SARs") | Long Term Incentive Plan (the "Plan")
Number of Stock Options
Total shares issues			1,526,835
Market price at the time of issuance			$8.87
vesting percentage			33.00%
Vesting period			3 years
Fair value of share ( in dollars per share)	$4.80		$4.53
Aggregate fair value	300,000
Stock compensation expense	$300,000

Segment_Information_Details

Segment Information (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
	segment
Segment Information
Number of geographic operating segments	2
Segment Information
Operating costs and expense	$63,257	$47,293
Operating income (loss)	-63,257	-47,293
Other income (expense)	-18,360	-9,622
Net income (loss)	-81,617	-56,915
Additions to Property and Equipment, net	473,117	144,264
United States
Segment Information
Operating costs and expense	51,741	31,027
Operating income (loss)	-51,741	-31,027
Additions to Property and Equipment, net	164,343	21,376
West Africa
Segment Information
Operating costs and expense	11,516	16,266
Operating income (loss)	-11,516	-16,266
Additions to Property and Equipment, net	$308,774	$122,888