Cobalt International Energy 10-K 2 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Jan. 31, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Entity Registrant Name	Cobalt International Energy, Inc.
Entity Central Index Key	1,471,261
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Trading Symbol	CIE
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 66.6
Entity Common Stock, Shares Outstanding		29,924,817
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 431,646	$ 613,534
Restricted cash	11,274	2,517
Joint interest and other receivables	176,320	167,573
Other current assets	38,643	23,149
Short-term investments		340,418
Total current assets	657,883	1,147,191
Oil and natural gas properties, net of accumulated depletion of $60,516 and $20,204 as of December 31, 2017 and 2016, respectively	916,941	1,078,885
Other property, net of accumulated depreciation and amortization of $9,827 and $8,426, as of December 31, 2017 and 2016, respectively	2,502	3,902
Other assets	19,428	500
Total assets	1,596,754	2,230,478
Current liabilities:
Trade and other accounts payable	24,483	36,954
Accrued liabilities	136,911	227,418
Accrued contract amendment costs		19,582
Angolan preliminary consideration		250,000
Total current liabilities	161,394	533,954
Long-term debt		2,479,349
Long-term derivative liabilities		50,123
Asset retirement obligations	7,394	6,523
Other long-term liabilities	1,577	1,863
Liabilities subject to compromise	3,220,337
Commitments and contingencies
Stockholders' Equity:
Common stock, $0.01 par value per share; 133,333,333 shares authorized, 29,640,353 and 29,422,864 issued and outstanding as of December 31, 2017 and 2016, respectively	296	294
Additional paid-in capital	4,239,746	4,223,729
Accumulated deficit	(6,033,990)	(5,065,357)
Total stockholders' equity	(1,793,948)	(841,334)
Total liabilities and stockholders' equity	$ 1,596,754	$ 2,230,478

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Oil and natural gas properties, accumulated depletion (in dollars)	$ 60,516	$ 20,204
Other property, accumulated depreciation and amortization (in dollars)	$ 9,827	$ 8,426
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	133,333,333	133,333,333
Common stock, shares issued	29,640,353	29,422,864
Common stock, shares outstanding	29,640,353	29,422,864

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Oil, natural gas and natural gas liquids revenues	$ 53,891	$ 16,805
Operating costs and expenses:
Seismic and exploration costs	47,477	58,170	$ 61,844
Dry hole costs and impairments	328,910	1,967,180	462,234
Loss on amendment of contract		95,908
Lease operating expenses	11,066	7,574
General and administrative expenses	104,558	127,860	110,634
Accretion expense	1,179	550	99
Depreciation, depletion and amortization	41,712	21,983	3,881
Total operating costs and expenses	534,902	2,279,225	638,692
Operating loss	(481,011)	(2,262,420)	(638,692)
Other (expense) income, net:
Other income	17,780		1,555
Loss on derivatives	(15,666)	(2,505)
Interest income	5,953	4,661	6,087
Interest expense	(162,542)	(83,045)	(63,376)
Reorganization expenses	(332,772)
Total other expense, net	(487,247)	(80,889)	(55,734)
Net loss	$ (968,258)	$ (2,343,309)	$ (694,426)
Basic and diluted loss per share:	$ (32.76)	$ (85.27)	$ (25.42)
Weighted average common shares outstanding (basic and diluted)	29,556	27,482	27,320

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Balance at Dec. 31, 2014	$ 2,114,266	$ 272	$ 4,141,616	$ (2,027,622)
Equity-based compensation	26,297		26,297
Net loss	(694,426)			(694,426)
Balance at Dec. 31, 2015	1,446,137	272	4,167,913	(2,722,048)
Common stock issued for restricted stock		2	(2)
Common stock issued in debt exchange	39,595	20	39,575
Equity-based compensation	16,243		16,243
Net loss	(2,343,309)			(2,343,309)
Balance at Dec. 31, 2016	(841,334)	294	4,223,729	(5,065,357)
Balance (Accounting Standards Update 2016-09) at Dec. 31, 2016			375	(375)
Common stock issued for restricted stock		2	(2)
Equity-based compensation	11,020		11,020
Effect of equity award modification	4,624		4,624
Net loss	(968,258)			(968,258)
Balance at Dec. 31, 2017	$ (1,793,948)	$ 296	$ 4,239,746	$ (6,033,990)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net loss	$ (968,258)	$ (2,343,309)	$ (694,426)
Adjustments to reconcile net loss to net cash used in operating activities:
Dry hole costs and impairments	328,910	1,967,180	462,234
Equity-based compensation	10,932	14,889	26,297
Accretion expense	1,179	550	99
Depreciation and amortization	41,712	21,983	3,881
Loss on derivatives	15,666	2,505
Amortization of premium (accretion of discount) on investments	6	(242)	14,483
Amortization of debt discount	41,497	77,041	89,662
Noncash reorganization expenses	331,822
Other	(261)	(213)	(1,555)
Changes in operating assets and liabilities:
Joint interest and other receivables	(7,221)	44,679	(151,334)
Other current assets	(8,566)	71,323	(27,528)
Trade and other accounts payable	405	20,138	2,681
Accrued liabilities	(8,170)	(62,058)	272,065
Accrued contract amendment costs	(19,582)	19,582
Other	(4,582)	287	1,795
Net cash flows used in operating activities	(244,511)	(165,665)	(1,646)
Cash flows from investing activities
Additions to oil and natural gas properties	(250,800)	(687,892)	(915,861)
Capital expenditures for other property		(3,479)	(4,808)
Proceeds from maturity of investment securities	867,355	3,390,112	1,999,421
Purchase of investment securities	(528,472)	(2,545,911)	(1,192,873)
Net cash flows provided by (used in) investing activities	88,083	152,830	(114,121)
Cash flows from financing activities
Proceeds from issuance of long-term debt		490,000
Payment of debt issuance costs			(4,068)
Payments to settle equity-based compensation awards	(1,285)
Net cash flows (used in) provided by financing activities	(1,285)	490,000	(4,068)
(Decrease) increase in cash, cash equivalents and restricted cash	(157,713)	477,165	(119,835)
Cash, cash equivalents and restricted cash, beginning of year	616,051	138,886	258,721
Cash, cash equivalents and restricted cash, end of year	$ 458,338	$ 616,051	$ 138,886

Organization and Nature of Busi

Organization and Nature of Business	12 Months Ended
	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Nature of Business	NOTE 1. ORGANIZATION AND NATURE OF BUSINESS Cobalt International Energy, Inc., together with its wholly–owned subsidiaries (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 Company operates in one reportable segment as its chief operating decision maker, the Chief Executive Officer, assesses performance and allocates resources based on the consolidated results of its business. Chapter 11 Cases On December 14, 2017 (the “Petition Date”), the Company and certain of its subsidiaries (collectively, the “Debtors”) filed voluntary petitions for relief (collectively, the “Chapter 11 Cases”) under Chapter 11 of the United States Bankruptcy Code (the “Bankruptcy Code”) in the United States Bankruptcy Court for the Southern District of Texas (the “Bankruptcy Court”). The Chapter 11 Cases have been consolidated for procedural purposes only and are being jointly administered under the caption “ In re Cobalt International Energy, Inc., et al. www.kccllc.net/cobalt On December 21, 2017, an official committee of unsecured creditors was appointed in the Chapter 11 Cases. No trustee has been appointed. The Debtors are currently operating their business and properties as debtors–in–possession subject to the jurisdiction of the Bankruptcy Court and in accordance with the applicable provisions of the Bankruptcy Code and the orders of the Bankruptcy Court. To ensure continued ordinary course operations, the Company received approval from the Bankruptcy Court on a variety of “first day” motions, including motions that authorize the Company to pay employee wages and benefits, pay taxes and certain governmental fees and charges, maintain its existing cash management system and other customary relief. Subject to certain exceptions provided for in Section 362 of the Bankruptcy Code, all judicial and administrative proceedings against the Debtors or its property were automatically enjoined, or stayed, as of the Petition Date. In addition, the filing of new judicial or administrative actions against the Debtors or its property for claims arising prior to the Petition Date was automatically enjoined. This prohibits, for example, the Debtors’ lenders or noteholders from pursuing claims for defaults under the Debtors’ debt agreements and the Debtors’ contract counterparties from pursuing claims for defaults under their contracts. Accordingly, unless the Bankruptcy Court agrees to lift the automatic stay, all of the Debtors’ prepetition liabilities and obligations will be settled or compromised under the Bankruptcy Code as part of the Chapter 11 Cases. The Company intends to consummate a sale of all or substantially all of the Debtors’ assets in the Chapter 11 Cases. On the Petition Date, the Debtors filed a motion seeking Bankruptcy Court approval of certain bidding procedures and a timeline for the sale process. On January 25, 2018, the Bankruptcy Court entered the Order (I) Approving Bidding Procedures for the Sale of the Debtors’ Assets, (II) Scheduling an Auction, (III) Approving the Form and Manner of Notice Thereof, (IV) Scheduling Hearing and Objection Deadlines with Respect to the Debtors’ Disclosure Statement and Plan Confirmation, and (V) Granting Related Relief Under the priority scheme established by the Bankruptcy Code, unless creditors agree otherwise, prepetition liabilities and postpetition liabilities must be satisfied in full before the holders of the Company’s common stock are entitled to receive any distribution or retain any property under a chapter 11 plan. The ultimate recovery to creditors and/or stockholders, if any, will not be determined until confirmation and implementation of a chapter 11 plan. No assurance can be given as to what distributions, if any, will be made to any of the Company’s creditors or stockholders. The Company’s chapter 11 plan could result in any of the holders of its liabilities and/or securities, including its common stock, receiving no distribution on account of their interests and cancellation of their holdings. Moreover, a chapter 11 plan can be confirmed, under the Bankruptcy Code, even if the holders of the Company’s common stock vote against the plan and even if the plan provides that the holders of the common stock receive no distribution on account of their equity interests. Accounting Standards Codification 852–10, Reorganizations The Company’s non–US subsidiaries are non–debtors and will be accounted for under accounting principles generally accepted in the United States for entities not in bankruptcy and outside the scope of ASC 852–10. These are minor subsidiaries. The only material assets of these non–debtor entities are $163.1 million of joint interest receivables, and the only material liabilities of these entities are $96.1 million of social obligation payments and Angolan consumption tax and withholding on services. The only material expense of the non–debtor entities is $45.3 million of dry hole costs and impairments related to the Company’s exploratory well and leaseholds in Gabon. There have been no material cash flows in any of these non–debtor entities. Liabilities Subject to Compromise Liabilities subject to compromise in the Company’s consolidated financial statements include pre–petition liabilities that may be affected by a chapter 11 plan at the amounts expected to be allowed, even if they may be settled for lesser amounts. If there is uncertainty about whether a secured claim is undersecured, or will be impaired under the chapter 11 plan, the entire amount of the claim is included in liabilities subject to compromise. Differences between liabilities the Company has estimated and the claims to be filed will be investigated and resolved in connection with the claims resolution process in the Chapter 11 Cases. The Company will continue to evaluate these liabilities throughout the Chapter 11 Cases and adjust amounts as necessary. Such adjustments may be material. The following table summarizes the components of liabilities subject to compromise included in the Company’s consolidated balance sheets as of December 31: 2017 Long-term debt $ 2,939,693 Angolan preliminary consideration 250,000 Accrued interest 25,537 Accrued liabilities 2,249 Trade and other accounts payable 2,858 Total $ 3,220,337 Costs of Reorganization The Debtors have incurred and will continue to incur significant costs associated with the Chapter 11 Cases. The amount of these costs, which are being expensed as incurred, are expected to significantly affect the Company’s results. The following table summarized the components included in “Reorganization expenses” in the Company’s consolidated statements of operations: 2017 Long-term debt discounts and issuance costs $ 331,822 Advisory and professional fees 950 Total $ 332,772 Ability to Continue as a Going Concern Given the uncertainty surrounding the Chapter 11 Cases, there is substantial doubt about the Company’s ability to continue as a going concern. The accompanying consolidated financial statements have been prepared on a going concern basis, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business. The consolidated financial statements do not include any adjustments relating to the recoverability and classification of assets and their carrying amounts, or the amount and classification of liabilities that may result should the Company be unable to continue as a going concern. While operating as debtors–in–possession under chapter 11 of the Bankruptcy Code, the Debtors may sell or otherwise dispose of or liquidate assets or settle liabilities in amounts other than those reflected in the Company’s consolidated financial statements, subject to the approval of the Bankruptcy Court or otherwise as permitted in the ordinary course of business. Further, a chapter 11 plan could materially change the amounts and classifications in the Company’s historical consolidated financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	NOTE 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation The consolidated financial statements include the accounts of the Company and its majority–owned subsidiaries (“we,” “our” or “us”). All significant intercompany accounts and transactions have been eliminated in consolidation. In the Notes to Consolidated Financial Statements, all dollar and share amounts in tabulations are in thousands of dollars and shares, respectively, unless otherwise indicated. On June 16, 2017, we effected a one–for–fifteen reverse stock split of our common stock through an amendment to our second amended and restated certificate of incorporation. As of the effective time of the reverse stock split, every 15 shares of issued and outstanding common stock were converted into one share of common stock, without any change in par value. The amendment to our second amended and restated certificate of incorporation also reduced the number of our authorized shares of common stock from 2.0 billion shares to 133.3 million shares. No fractional shares were issued in connection with the reverse stock split. Instead, each fractional share was rounded up to the nearest whole share of common stock. However, any fractional shares resulting from adjustments to the number of shares underlying stock options and stock appreciation rights were rounded down to the nearest whole share of common stock. All references to shares of common stock, all per share data and all equity compensation activity for all periods presented in the consolidated financial statements and notes to the consolidation financial statements have been adjusted to reflect the reverse stock split on a retroactive basis. Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and judgments that affect the reported amounts of assets and liabilities, 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. We base our estimates and judgments on historical experience and on various other assumptions and information that are believed to be reasonable under the circumstances. Estimates and assumptions about future events and their effects cannot be perceived with certainty and, accordingly, these estimates may change as new events occur, as more experience is acquired, as additional information is obtained and as our operating environment changes. While we believe that the estimates and assumptions used in the preparation of the consolidated financial statements are appropriate, actual results could differ from those estimates. Cash and Cash Equivalents We consider all highly liquid investments with an original maturity of three months or less at the time of purchase to be cash equivalents. All of our cash and cash equivalents are maintained with several major financial institutions in the United States. Deposits with these financial institutions may exceed the amount of insurance provided on such deposits; however, we regularly monitor the financial stability of these financial institutions and believe that we are not exposed to any significant default risk. Restricted Cash Our restricted cash is invested in interest–bearing account. As of December 31, 2017, $15.4 million of our restricted cash is being held in escrow for the benefit of the insured persons under our settlements with XL Specialty Insurance Company (“XL”) and Axis Insurance Company (“Axis”). As of December 31, 2017 and 2016, $11.3 million and $2.5 million, respectively, of our restricted cash serves as collateral for certain of our obligations. Joint Interest and Other Receivables Joint interest receivables result from billing shared costs under the respective operating agreements to our partners. Accounts receivable from oil, natural gas and natural gas liquids sales are recorded at the invoiced amount and do not bear interest. We routinely assess the financial strength of our customers and partners and bad debts are recorded based on an account–by–account review after all means of collection have been exhausted, and the potential recovery is considered remote. As of December 31, 2017 and 2016, we did not have any reserves for doubtful accounts. We also did not have any off–balance sheet credit exposure related to our customers. Investments As of December 31, 2017, all of our investments in marketable debt securities had matured and were included in “Cash and cash equivalents” in our consolidated balance sheet. Accordingly, there was no potential for other–than-temporary impairments (“OTTI”) as in prior periods. As of December 31, 2016, our investments in marketable debt securities were classified as held–to–maturity as we had the positive intent and ability to hold the investments until they matured. Investments with original maturities of greater than three months and remaining maturities of less than one year were classified as short–term investments. These debt securities were carried at amortized cost and the carrying value of these securities was adjusted for amortization of premiums and accretion of discounts to maturity over the life of the securities. As the estimated fair value of each investment approximates its amortized cost, there were no significant unrecognized holding gains or losses as of December 31, 2016. Income related to these securities was reported as a component of interest income in our consolidated statements of operations. Investments were considered to be impaired when a decline in fair value was determined to be other–than–temporary. We conducted a regular assessment of our debt securities with unrealized losses to determine whether these securities had OTTI. This assessment considered, 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 we intended to sell or whether it was more likely than not that we would be required to sell the debt securities. As of December 31, 2016, we had no OTTI in our debt securities. Property and Depreciation, Depletion and Amortization Our oil, natural gas and natural gas liquids producing activities are accounted for under the successful efforts method of accounting. Under this method, costs to drill exploratory wells that do not find proved reserves, geological and geophysical costs and costs of carrying and retaining unproved properties are charged to expense as incurred. For 2017, 2016 and 2015, we recorded dry hole costs and impairments of $282.6 million, $213.5 million and $188.0 million, respectively, to expense costs associated with the drilling of exploratory wells that did not find proved reserves. Costs for unproved leasehold properties and exploratory wells that find reserves that cannot yet be classified as proved are capitalized if the well has found a sufficient quantity of reserves to justify its completion as a producing well and we are making sufficient progress assessing the reserves and the economic and operating viability of the project. Often, the ability to move into the development phase and record proved reserves is dependent on obtaining permits and government or partner approvals, the timing of which is ultimately beyond our control. Exploratory well costs remain suspended as long as we are actively pursuing such approvals and permits, and believe they will be obtained. For complex exploratory projects, it is not unusual to have exploratory wells remain suspended on the balance sheet for several years while additional appraisal drilling and seismic work is performed on the field or while we seek government or partner approval of development plans. Our assessment of suspended exploratory well costs is continuous until a determination is made to either sanction the project or to expense the well costs as dry hole costs as sufficient progress has not been made in assessing the reserves and the economic and operating viability of the project. In 2016, we recorded an impairment charge of dry hole costs of $1,276.4 million to expense costs associated with our Angolan exploratory wells (see Note 3). The capitalized costs of our producing oil and natural gas properties are depreciated and depleted by the units–of–production method based on the ratio of current production to estimated total net proved reserves as estimated by independent petroleum engineers. Proved developed reserves are used in computing unit rates for drilling and development costs and total proved reserves are used for depletion rates of leasehold costs. Other property is stated at cost less accumulated depreciation, which is computed using the straight–line method based on estimated economic lives ranging from three to ten years. We expense costs for maintenance and repairs in the period incurred. Significant improvements and betterments are capitalized if they extend the useful life of the asset. Impairment of Oil and Natural Gas Properties We evaluate our proved oil and natural gas properties and related equipment and facilities for impairment whenever events or changes in circumstances indicate that the carrying amounts of such properties may not be recoverable. The determination of recoverability is made based upon estimated undiscounted future net cash flows. The amount of impairment loss, if any, is determined by comparing the fair value, as determined by a discounted cash flow analysis, with the carrying value of the related asset. In 2015, we recorded impairment charges of $256.8 million related to our proved oil and natural gas properties (see Note 5). No impairment charges were recorded in 2017 or 2016 related to our proved oil and natural gas properties. Oil and natural gas leases for unproved properties with a carrying value greater than $1.0 million are assessed individually for impairment based on our current exploration plans and an allowance for impairment is provided if impairment is indicated. Leases that are individually less than $1.0 million in carrying value or are near expiration are amortized over the terms of the leases at rates that provide for full amortization of leases upon lease expiration. These leases have expiration dates ranging from 2018 through 2026. For 2017, 2016 and 2015, we recorded impairment charges of $46.2 million, $66.6 million and $26.9 million, respectively, related to our leases for unproved oil and natural gas properties. In 2016, we also recorded an impairment charge of $353.4 million related to our Angolan leases in conjunction with the write-off of our Angolan exploratory well costs (see Note 3). Asset Retirement Obligations An asset retirement obligation (“ARO”) represents the future abandonment costs of tangible assets, such as wells, service assets, and other facilities. We record an ARO and capitalize the asset retirement cost in oil and natural gas properties in the period in which the retirement obligation is incurred based upon the fair value of an obligation to perform site reclamation, dismantle facilities or plug and abandon wells. After recording these amounts, the ARO is accreted to its future estimated value using an assumed cost of funds and the additional capitalized costs are depreciated on a unit–of–production basis. If the ARO is settled for an amount other than the recorded amount, a gain or loss is recognized. Embedded Derivatives Our first lien senior secured notes due 2021 (the “First Lien Notes”) and our second lien senior secured notes due 2023 (the “Second Lien Notes”) include features which were determined to be embedded derivatives requiring bifurcation and accounting as separate financial instruments. The embedded derivatives were initially recorded at fair value and were subject to remeasurement as of each balance sheet date. We elected not to designate our embedded derivatives as hedging instruments. Changes in the fair value of these embedded derivatives were recorded immediately to earnings in “Loss on derivatives” in our consolidated statements of operations. Revenue Recognition Oil, natural gas and natural gas liquids revenues are recognized when production is sold to a purchaser at fixed or determinable prices, when delivery has occurred and title has transferred and collectability of the revenue is reasonably assured. We follow the sales method of accounting for natural gas revenues. Under this method of accounting, revenues are recognized based on volumes sold, which may differ from the volume to which we are entitled based on our working interest. An imbalance is recognized as a liability only when the estimated remaining reserves will not be sufficient to enable the under–produced owner(s) to recoup its entitled share through future production. Under the sales method, no receivables are recorded where we have taken less than our share of production. There were no significant natural gas imbalances at December 31, 2017 and 2016. Income Taxes We use the liability method to determine our income tax provisions, under which current and deferred tax liabilities and assets are recorded in accordance with enacted tax laws and rates. Under this method, the amounts of deferred tax liabilities and assets at the end of each period are determined using the tax rate expected to be in effect when taxes are actually paid or recovered. Valuation allowances are established to reduce deferred tax assets when it is more likely than not that some portion or all of the deferred tax assets will not be realized. Concentration of Credit Risk Our oil, natural gas and natural gas liquids revenues are derived principally from uncollateralized sales to customers in the oil and natural gas industry; therefore, our customers may be similarly affected by changes in economic and other conditions within the industry. We have experienced no credit losses on such sales in the past. In 2017 and 2016, one customer accounted for 95.0% and 96.5%, respectively, of our consolidated oil, natural gas and natural gas liquids revenues. We believe that the loss of this customer would have a temporary effect on our revenues but, that over time, we would be able to replace this customer. Recently Issued Accounting Standards In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014–09, Revenue from Contracts with Customers. In February 2016, the FASB issued ASU No. 2016-02, Leases In March 2016, the FASB issued ASU No. 2016-09, Compensation – Stock Compensation No other new accounting pronouncements issued or effective during 2017 have had or are expected to have a material impact on our consolidated financial statements.

Angola Settlement

Angola Settlement	12 Months Ended
	Dec. 31, 2017
Loss Contingency [Abstract]
Angola Settlements	NOTE 3. ANGOLA SETTLEMENT In August 2015, we executed a Purchase and Sale Agreement (the “Sale Agreement ”) with Sociedade Nacional de Combustíveis de Angola—Empresa Pública (“Sonangol”) for the sale by us to Sonangol of the 40% working interests in each of Block 20 and Block 21 offshore Angola. The requisite Angolan government approvals were not received within one year from the execution date and the Sale Agreement terminated by its terms in August 2016. In 2016, we recorded an impairment of $1,629.8 million related to our Angolan assets in accordance with Accounting Standards Codification 932, Extractive Activities – Oil and Gas In March 2017, we submitted a Notice of Dispute to Sonangol pursuant to the Sale Agreement. We then filed a filed a Request for Arbitration (“RFA”) with the International Chamber of Commerce (“ICC”) against Sonangol for breach of the Sale Agreement. Through this arbitration proceeding, we are requesting an award against Sonangol in excess of $2.0 billion, plus applicable interest and costs. In July 17, 2017, Sonangol filed an Answer to our RFA and Counterclaim, asking for repayment of the $250.0 million initial payment that Sonangol made to us under the Sale Agreement. We also filed a separate RFA with the ICC against Sonangol Pesquisa e Produção, S.A. (“Sonangol P&P”) On December 19, 2017, certain of our subsidiaries executed a settlement agreement (the “Agreement”) with Sonangol and Sonangol P&P to resolve all disputes and transition our interests in Blocks 20 and 21 offshore Angola to Sonangol for $500.0 million. Pursuant to the Agreement, Sonangol is required to pay an initial non–refundable payment of $150.0 million on or before February 23, 2018 (the “Initial Payment”) and the final payment of $350.0 million on or before July 1, 2018 (the “Final Payment”). On January 25, 2018, the Bankruptcy Court entered an Order Approving Debtors’ Motion for Entry of an Order (I) Authorizing Performance Under Settlement Agreement, (II) Approving Settlement Agreement, and (III) Granting Related Relief On February 21, 2018, we received the Initial Payment, and, in accordance with the Agreement, we (i) notified the relevant ICC arbitral tribunal of the agreement between Sonangol P&P and us to terminate the proceedings related to the joint interest receivable owed to us for operations on Block 21 offshore Angola and (ii) notified the relevant ICC arbitral tribunal of the agreement between Sonangol and us to extend the procedural timetable by an additional four months for the proceedings related to the PSA (the “PSA Arbitration”). In accordance with the Agreement, we and Sonangol are finalizing definitive documentation to implement our exit from Angola and to extinguish all debts and obligations of us and Sonangol to each other that have not already been extinguished pursuant to the Agreement. Our claims in the PSA Arbitration will be extinguished upon our receipt of the Final Payment, which is due by July 1, 2018. Within 48 hours of receipt of the Final Payment, we are required under the Agreement to notify the ICC arbitral tribunal in the PSA Arbitration of our agreement to terminate the proceedings related to the dispute arising from the failed Sale Agreement.

Investments

Investments	12 Months Ended
	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Investments	NOTE 4. INVESTMENTS Our investments in held–to–maturity securities consist of the following as of December 31: 2017 (1) 2016 Corporate securities $ — $ 227,854 Commercial paper — 292,466 U.S. Treasury securities — 161,778 Total $ — $ 682,098 (1) These investments are recorded in our consolidated balance sheets as follows as of December 31: 2017 2016 Cash and cash equivalents $ — $ 341,680 Short-term investments (1) — 340,418 $ — $ 682,098 (1) As of December 31, 2016, $9.1 million of these investments served as collateral for certain of our obligations.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	NOTE 5. FAIR VALUE MEASUREMENTS The fair value hierarchy has three levels based on the reliability of the inputs used to determine fair value. Level 1 refers to fair values determined based on quoted prices in active markets for identical assets or liabilities. Level 2 refers to fair values determined based on quoted prices for similar assets and liabilities in active markets or inputs that are observable for the asset or liability, either directly or indirectly through market corroboration. Level 3 refers to fair values determined based on our own assumptions used to measure assets and liabilities at fair value. Recurring Basis The commencement of the Chapter 11 Cases triggered the event of default provision of our embedded derivatives and the subsequent recognition of $44.4 million and $54.5 million of applicable premiums (as defined in the respective indentures) for the First Lien Notes and Second Lien Notes, respectively. These premiums are considered to be part of the principal due for the First Lien Notes and Second Lien Notes and are included in “Liabilities subject to compromise” in our consolidated balance sheets. The reconciliation of changes in the fair value of our embedded derivatives is as follows for the years ended December 31: 2017 2016 Beginning of period $ 50,123 $ — Issuance of First Lien Notes and Second Lien Notes — 47,618 Issuance of additional Second Lien Notes 33,110 — Change in fair value 15,666 2,505 Reclass to long-term debt (98,899 ) — End of period $ — $ 50,123 The following table represents the fair value hierarchy for our liabilities required to be measured at fair value on a recurring basis: Fair Value Measurements at the End of the Reporting Period: Fair Value Level 1 Level 2 Level 3 As of December 31, 2016: Embedded derivative liabilities: First Lien Notes $ 27,012 $ — $ — $ 27,012 Second Lien Notes 23,111 — — 23,111 Total $ 50,123 $ — $ — $ 50,123 The fair values of these embedded derivatives were estimated using the “with” and “without” method. Using this methodology, the First Lien Notes and Second Lien Notes were first valued with the embedded derivatives (the “with” scenario) and subsequently valued without the embedded derivative (the “without” scenario). The fair values of the embedded derivatives were estimated as the difference between the fair values of the First Lien Notes and Second Lien Notes in the “with” and “without” scenarios. The fair values of the First Lien Notes and Second Lien Notes in the “with” and “without” scenarios were estimated using a risk–neutral probability of default model. Significant Level 3 assumptions used in the valuation of the embedded derivatives were the fair values of our long–term debt, the expected recovery rates, the risk–neutral probability of default and the risk–free rates. Nonrecurring Basis In 2015, as a result of a reduction in future net cash flows, we recognized a $256.8 million impairment charge to write down proved oil and natural gas properties to their fair value of $68.4 million. The fair value was determined using the income approach and was based on the expected present value of the future net cash flows from estimated reserves. Significant Level 3 assumptions associated with the calculation of discounted cash flows used in the impairment analysis included estimates of future prices, production costs, development expenditures, anticipated production of our estimated reserves, appropriate risk–adjusted discount rates and other relevant data. Financial Instruments The estimated fair values of our financial instruments have been determined at discrete points in time based on relevant market information. Our financial instruments consist of cash and cash equivalents, joint interest and other receivables, held–to–maturity investments, accounts payable and accrued liabilities. The carrying amounts of our financial instruments, other than held–to–maturity–investments and long–term debt, approximate fair value because of the short–term nature of the items. There were no significant unrecognized holding gains or losses related to our held–to–maturity investments as of December 31, 2016. Accordingly, the carrying value of our held–to–maturity investments approximates their fair value. Our held–to–maturity investments were not traded on a public exchange and the fair value of these investments was based on inputs using valuations obtained from independent brokers. As these valuations used readily observable market parameters that were actively quoted and could be validated through external sources, we categorized these investments as Level 2. The estimated fair value of our long–term debt is as follows as of December 31: 2017 2016 10.75% first lien notes due 2021 $ 542,500 $ 482,250 7.75% second lien notes due 2023 874,563 327,449 2.625% convertible senior notes due 2019 167,949 305,378 3.125% convertible senior notes due 2024 216,396 332,344 $ 1,801,408 $ 1,447,421 The fair values of our long–term debt were estimated using quoted market prices. As these valuations use quoted prices in active markets for identical assets or liabilities, we have categorized the long–term debt as Level 1.

Oil and Natural Gas Properties

Oil and Natural Gas Properties	12 Months Ended
	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Oil and Natural Gas Properties	NOTE 6. OIL AND NATURAL GAS PROPERTIES Oil and natural gas properties consisted of the following as of December 31: 2017 2016 Proved oil and natural gas properties: Well and development costs $ 127,005 $ 118,245 Accumulated depletion (60,516 ) (20,204 ) Total proved properties 66,489 98,041 Unproved oil and natural gas properties: Oil and natural gas leaseholds 556,771 651,295 Accumulated valuation allowance (457,520 ) (507,198 ) 99,251 144,097 Exploratory wells in process 751,201 836,747 Total unproved properties 850,452 980,844 Total oil and natural gas properties, net $ 916,941 $ 1,078,885 Capitalized Exploratory Well Costs The following tables reflect the net changes in and the cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs): 2017 2016 2015 Beginning of period $ 836,747 $ 1,727,181 $ 1,186,464 Additions to capitalized exploration Exploratory well costs 137,538 499,985 630,395 Capitalized interest 59,558 99,541 87,683 Amounts charged to expense (1) (282,642 ) (1,489,960 ) (177,361 ) End of period $ 751,201 $ 836,747 $ 1,727,181 (1) Amounts represent dry hole costs and impairments related to exploratory wells which did not encounter commercial hydrocarbons or where it was determined that sufficient progress was not being made. 2017 2016 Cumulative costs: Exploratory well costs $ 437,011 $ 582,115 Capitalized interest 314,190 254,632 $ 751,201 $ 836,747 Wells costs capitalized for a period greater than one year after completion after drilling (included in table above) $ 719,639 $ 609,893 As of December 31, 2017, capitalized exploratory well costs that have been suspended longer than one year are associated with our Anchor and North Platte discoveries. As of December 31, 2016, capitalized exploratory well costs that have been suspended longer than one year are associated with our Shenandoah, North Platte, Anchor, and Gabon 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. We believe these discoveries exhibit sufficient indications of hydrocarbons to justify potential development and are 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.

Long-term Debt, Net

Long-term Debt, Net	12 Months Ended
	Dec. 31, 2017
Long Term Debt [Abstract]
Long-term Debt, Net	NOTE 7. LONG–TERM DEBT, NET Long–term debt, net consisted of the following as of December 31: 2017 2016 10.75% first lien notes due 2021 Principal outstanding (1) $ 544,444 $ 500,000 Unamortized discount (2) — (34,416 ) Carrying amount 544,444 465,584 7.75% second lien notes due 2023 Principal outstanding (1) 989,187 584,732 Unamortized discount (3) — (54,856 ) Carrying amount 989,187 529,876 2.625% convertible senior notes due 2019: Principal outstanding 619,167 763,446 Unamortized discount and debt issuance costs (4) — (109,689 ) Carrying amount 619,167 653,757 3.125% convertible senior notes due 2024: Principal outstanding 786,895 1,204,145 Unamortized discount and debt issuance costs (5) — (374,013 ) Carrying amount 786,895 830,132 Total debt 2,939,693 2,479,349 Long-term debt subject to compromise (2,939,693 ) — Total long-term debt $ — $ 2,479,349 (1) Includes applicable premiums of $44.4 million for the First Lien Notes and $54.5 million for the Second Lien Notes (see Note 5) (2) (3) (4) (5) Acceleration of Debt Obligations The commencement of the Chapter 11 Cases constituted an event of default that accelerated our obligations under all of our long–term debt obligations. Any efforts to enforce such obligations are automatically stayed as a result of the filing of the Chapter 11 Cases and the holders’ rights of enforcement in respect of these debt obligations are subject to the applicable provisions of the Bankruptcy Code. We are making adequate protection payments with respect to our First Lien Notes consisting of the payment of interest (at the default rate of 11.75%) and the payment of all reasonable fees and expenses of professionals retained by the holders of the First Lien Notes. We are also making adequate protection payments with respect to our remaining long–term debt in the form of the payment of all reasonable fees and expenses of professionals retained by the holders of the debt. Debt Exchanges In December 2016, we consummated a debt exchange and financing transaction (the “2016 Transaction”) with certain holders (the “2016 Holders”) of our outstanding 2.625% Convertible Senior Notes due 2019 (the “2019 Notes”) and 3.125% Convertible Senior Notes due 2024 (the “2024 Notes”). The 2016 Transaction consisted of: (i) the issuance of $500.0 million aggregate principal amount of our First Lien Notes to Holders for cash at a price of 98% and (ii) the issuance of $584.7 million aggregate principal amount of our Second Lien Notes and 30.0 million shares of our common stock to Holders in exchange for $616.6 million aggregate principal amount of 2019 Notes and $95.9 million aggregate principal amount of 2024 Notes held by the Holders. In addition, we recognized embedded derivative liabilities of $24.8 million and $22.8 million for our First Lien Notes and Second Lien Notes, respectively. We accounted for the 2016 Transaction as a debt modification as we determined that the terms of the new debt instruments were not substantially different from the terms of the original instruments. We did not recognize any gain or loss on the 2016 Transaction and prospectively adjusted the effective interest rates on the 2019 Notes and 2024 Notes. Costs related to the Transaction totaled $19.6 million and are included in “General and administrative expenses” in our consolidated statements of operations. In 2017, we consummated three follow–on debt exchange transactions (the “2017 Transactions”) with certain holders (the “2017 Holders”) of our outstanding 2019 Notes and 2024 Notes whereby we issued an aggregate principal amount of $350.0 million in additional Second Lien Notes in exchange for $144.3 million aggregate principal amount of the 2019 Notes and $417.2 million aggregate principal amount of the 2024 Notes held by the 2017 Holders. In addition, we recognized additional embedded derivative liabilities of $33.1 million for our Second Lien Notes. We accounted for the 2017 Transactions as troubled debt restructurings. We did not recognize any gain or loss on the 2017 Transactions and prospectively adjusted the effective interest rates on the 2019 Notes and 2024 Notes. Costs related to the Transactions totaled $3.0 million and are included in “General and administrative expenses” in our unaudited condensed consolidated statements of operations. 10.75% First Lien Notes The 10.75% First Lien Notes were issued on December 6, 2016 and mature on December 1, 2021. Interest is payable semi–annually in arrears on each June 1 and December 1 of each year. The First Lien Notes are initially guaranteed by all of our wholly–owned domestic subsidiaries (the “Guarantors”) and are secured, subject to certain exceptions, by a first priority lien on (i) substantially all of ours and the Guarantors’ assets and (ii) 65% of the shares of capital stock of Cobalt International Energy Overseas Ltd., which indirectly owns our working interests in our blocks offshore Angola and offshore Gabon (collectively, the “Collateral”). As of December 31, 2017, the First Lien Notes were reflected as “Liabilities subject to compromise” in our consolidated balance sheets with the carrying value equal to the face value of the notes. The unamortized discount of $29.3 million as of the Petition Date was expensed and recognized in “Reorganization expenses” in our consolidated statement of operations. 7.75% Second Lien Notes The 7.75% Second Lien Notes were issued pursuant to an indenture dated December 6, 2016 (as amended or supplemented from time to time, the “Second Lien Indenture”) and mature on December 1, 2023. Interest is payable semi–annually in arrears on each June 1 and December 1 of each year. The Second Lien Notes are guaranteed by the Guarantors and are secured, subject to certain exceptions, by a second priority lien on the Collateral. As of December 31, 2017, the Second Lien Notes were reflected as “Liabilities subject to compromise” in our consolidated balance sheets with the carrying value equal to the face value of the notes. The unamortized discount of $19.4 million as of the Petition Date was expensed and recognized in “Reorganization expenses” in our consolidated statement of operations. In addition, $2.6 million of accrued but unpaid interest is reflected as “Liabilities subject to compromise” in our consolidated balance sheets. We have not recognized any interest expense on our Second Lien Notes subsequent to the Petition Date. Unrecognized contractual interest expense on our Second Lien Notes for 2017 was $3.4 million. 2.625% Convertible Senior Notes due 2019 The 2019 Notes were issued under an indenture dated December 17, 2012 (the “2019 Indenture”) and mature December 1, 2019. Interest is payable semi–annually in arrears on June 1 and December 1 of each year. The 2019 Notes are senior unsecured obligations. The 2019 Notes may be converted at the option of the holder on the second scheduled trading day immediately preceding the maturity date, in multiples of $1,000 principal amount. The 2019 Notes are convertible at an initial conversion rate of 1.8682 shares of common stock per $1,000 principal amount, representing an initial conversion price of approximately $535.20 per share. The conversion rate is subject to adjustment upon the occurrence of certain events, as defined in 2019 Indenture, but will not be adjusted for any accrued and unpaid interest except in limited circumstances. We can satisfy the conversion obligation, at our option, in either cash, shares of common stock or a combination thereof. When the 2019 Notes were issued, we accounted for the debt and equity components of the 2019 Notes separately, as we have the option to settle the conversion obligation in cash. At the date of issuance, we calculated the fair value of the 2019 Notes, excluding the conversion feature, based on the fair value of similar non–convertible debt instruments. The difference between the cash proceeds and the estimated fair value represented the value which was assigned to the equity component and recorded as a debt discount. Prior to the Petition Date, the debt discount was being amortized using the effective interest rate method over the period from issuance to the maturity date of December 1, 2019. The carrying amount of the equity component of the 2019 Notes reported in additional paid in capital was initially valued at $381.4 million, which was net of $9.1 million of debt issuance costs allocated to the equity component. As the closing price of our common stock on December 31, 2017 was less than the initial conversion price for the 2019 Notes, the if–converted value of the 2019 Notes would be less than principal amount. Holders of the 2019 Notes who convert their notes in connection with a “make–whole fundamental change”, as defined in the 2019 Indenture, 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 2019 Indenture, holders of the 2019 Notes may require us 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 2019 Notes, plus accrued and unpaid interest, if any, to, but not including, the fundamental change repurchase date. As of December 31, 2017, the 2019 Notes were reflected as “Liabilities subject to compromise” in our consolidated balance sheets with the carrying value equal to the face value of the notes. The unamortized discount and debt issuance costs of $58.3 million and $3.9 million, respectively, as of the Petition Date was expensed and recognized in “Reorganization expenses” in our consolidated statement of operations. On December 1, 2017, we elected to defer the $8.1 million interest payment that was due on December 1, 2017. As of consequence of the commencement of the Chapter 11 Cases, such interest payment has not been made, and is classified as “Liabilities subject to compromise” in our consolidated balance sheets. In addition, $8.7 million of accrued but unpaid interest from December 1, 2017 through December 13, 2017 is reflected as “Liabilities subject to compromise” in our consolidated balance sheets. We have not recognized any interest expense on our 2019 Notes subsequent to the Petition Date. Unrecognized contractual interest expense on our 2019 Notes for 2017 was $0.8 million. 3.125% Convertible Senior Notes due 2024 The 2024 Notes were issued under an indenture dated May 13, 2014 (the “2024 Indenture”) and mature on May 15, 2024. Interest is payable semi–annually in arrears on May 15 and November 15 of each year. The 2024 Notes are senior unsecured obligations and ran equal in right of payment to the 2019 Notes. Prior to November 15, 2023, the 3.125% Notes are convertible only under certain circumstances as outlined in the 2024 Indenture. On or after November 15, 2023, the 2024 Notes may be converted at the option of the holder at any time on the second scheduled trading day immediately preceding the stated maturity date, in multiples of $1,000 principal amount. The 2024 Notes are convertible at an initial conversion rate of 2.8907 shares of common stock per $1,000 principal amount, representing an initial conversion price of approximately $345.90 per share. The conversion rate is subject to adjustment upon the occurrence of certain events, as defined in the 2024 Indenture, but will not be adjusted for any accrued and unpaid interest except in limited circumstances. We can satisfy the conversion obligation, at our option, in either cash, shares of common stock or a combination thereof. When the 2024 Notes were issued, we accounted for the debt and equity components of the 2024 Notes separately, as we have the option to settle the conversion obligation in cash. At the date of issuance, we calculated the fair value of the 2024 Notes, excluding the conversion feature, based on the fair value of similar non–convertible debt instruments. The difference between the cash proceeds and the estimated fair value represented the value which was assigned to the equity component and recorded as a debt discount. Prior to the Petition Date, the debt discount was being amortized using the effective interest rate method over the period from issuance to the maturity date of May 15, 2024. The carrying amount of the equity component of the 2024 Notes reported in additional paid in capital was initially valued at $464.7 million, which was net of $11.1 million of debt issuance costs allocated to the equity component. As the closing price of our common stock on December 31, 2017 was less than the initial conversion price for the 2024 Notes, the if–converted value of the 2024 Notes would be less than principal amount. Holders of the 2024 Notes who convert their notes in connection with a “make– whole fundamental change”, as defined in the 2024 Indenture, 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 2024 Indenture, holders of the 2024 Notes may require us 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 2024 Notes, plus accrued and unpaid interest, if any, to, but not including, the fundamental change repurchase date. As of December 31, 2017, the 2024 Notes were reflected as “Liabilities subject to compromise” in our consolidated balance sheets with the carrying value equal to the face value of the notes. The unamortized discount and debt issuance costs of $211.5 million and $9.4 million, respectively, as of the Petition Date was expensed and recognized in “Reorganization expenses” in our consolidated statement of operations. On November 15, 2017, we elected to defer the $12.3 million interest payment that was due on November 15, 2017. As of consequence of the commencement of the Chapter 11 Cases, such interest payment has not been made, and is classified as “Liabilities subject to compromise” in our consolidated balance sheets. In addition, $14.2 million of accrued but unpaid interest from November 15, 2017 through December 13, 2017 is reflected as “Liabilities subject to compromise” in our consolidated balance sheets. We have not recognized any interest expense on our 2024 Notes subsequent to the Petition Date. Unrecognized contractual interest expense on our 2024 Notes for 2017 was $1.2 million. Borrowing Base Facility Agreement In 2015, Cobalt GOM #1 LLC, an indirect, wholly-owned subsidiary, entered into a Borrowing Base Facility Agreement (the “Facility Agreement”) which provided for a limited recourse $150.0 million senior secured reserve–based term loan facility, with an amount available for borrowing at any time limited to a periodically adjusted borrowing base amount. In 2016, we terminated the Facility Agreement because the borrowing base amount under the Facility Agreement was expected to be materially reduced to a level that would not justify the ongoing expense of maintaining the facility. In conjunction with the termination, we wrote off $3.3 million of debt issuance costs associated with the facility agreement. We had no amounts outstanding under the Facility Agreement at any time it was in place. Maturities of Long–Term Debt The maturities of our long–term debt are as follows for the years ended December 31: Payments Due By Year 2018 2019 2020 2021 2022 Thereafter Principal outstanding $ 2,939,693 $ — $ — $ — $ — $ —

Asset Retirement Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2017
Asset Retirement Obligation [Abstract]
Asset Retirement Obligations	NOTE 8. ASSET RETIREMENT OBLIGATIONS The changes in ARO are as follows for the years ended December 31: 2017 2016 Beginning of period $ 6,523 $ 3,167 Additions 86 — Revisions (394 ) 2,806 Accretion 1,179 550 End of period $ 7,394 $ 6,523

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	NOTE 9. COMMITMENTS AND CONTINGENCIES We are currently, and from time to time we may become, involved in various legal and regulatory proceedings arising in the normal course of business. In November 2014, two purported stockholders, St. Lucie County Fire District Firefighters’ Pension Trust Fund and Fire and Police Retiree Health Care Fund, San Antonio, filed a class action lawsuit in the U.S. District Court for the Southern District of Texas on behalf of a putative class of all purchasers of our securities from February 21, 2012 through November 4, 2014 (the “St. Lucie lawsuit”). The St. Lucie lawsuit, filed against us and certain officers, former and current members of the Board of Directors, underwriters, and investment firms and funds, asserted violations of federal securities laws based on alleged misrepresentations and omissions in SEC filings and other public disclosures, primarily regarding compliance with the U.S. Foreign Corrupt Practices Act (“FCPA”) in our Angolan operations and the performance of certain wells offshore Angola. In December 2014, Steven Neuman, a purported stockholder, filed a substantially similar lawsuit against us and certain of our officers in the U.S. District Court for the Southern District of Texas on behalf of a putative class of all purchasers of our securities from February 21, 2012 through August 4, 2014 (the “Neuman lawsuit”). Like the St. Lucie lawsuit, the Neuman lawsuit asserted violations of federal securities laws based on alleged misrepresentations and omissions in SEC filings and other public disclosures regarding our compliance with the FCPA in our Angolan operations. In March 2015, the Court entered an order consolidating the Neuman lawsuit with the St. Lucie lawsuit (the “Consolidated Action”) and also entered an order in the Consolidated Action appointing Lead Plaintiffs and Lead Counsel. Lead Plaintiffs filed their consolidated amended complaint in May 2015. Among other remedies, the Consolidated Action seeks damages in an unspecified amount, along with an award of attorney fees and other costs and expenses to the plaintiffs. We filed a motion to dismiss the consolidated amended complaint in June 2015, and the other defendants also filed motions to dismiss. The Court denied our motion to dismiss in January 2016, and, in March 2016, the Court also denied our motion requesting that the Court certify its order on the motions to dismiss so that we may seek interlocutory appellate review of the order. In June 2017, the Court certified a class of all persons and entities who purchased or otherwise acquired our securities between March 1, 2011 and November 3, 2014. In July 2017, we filed a petition for permission to file an interlocutory appeal challenging the class certification order. On August 4, 2017, the Fifth Circuit Court of Appeals granted our petition for permission to file the interlocutory appeal. We filed our appeal on October 10, 2017 and briefing is now complete. On December 14, 2017, we filed a notice of suggestion on pendency of bankruptcy and the Court stayed the Consolidated Action the following day. The court presiding over our bankruptcy proceeding subsequently entered an order staying the Consolidated Proceeding in its entirety through April 20, 2018. On December 22, 2017, Plaintiffs moved to dismiss Cobalt from the Consolidated Action. The Court denied the motion without prejudice on January 24, 2018, holding that the Plaintiffs could reurge their motion 31 days after providing notice and an opportunity to object to class members via publication in Business Wire . In May 2016, Gaines, a purported stockholder, filed a derivative action in the 295th District Court in Harris County, Texas against us, as a nominal defendant, certain of our current and former officers and directors, and certain investment firms and funds. The lawsuit alleges that current and former officers and directors breached their fiduciary duties by making, and permitting us to make, alleged misrepresentations about two of our exploration wells offshore Angola; that certain officers received performance-based compensation in excess of what they were entitled; and that the investment firms and funds owed a fiduciary duty to us as controlling stockholders and breached that duty by engaging in insider trading. The lawsuit further alleges that demand was wrongfully refused. The plaintiff asserts claims for breach of fiduciary duty and unjust enrichment and seeks damages in an unspecified amount, disgorgement of profits, appropriate equitable relief, and an award of attorney fees and other costs and expenses. In July 2016, we filed our answer and special exceptions challenging the plaintiff’s standing to bring such claims against us. The Court heard arguments on our special exceptions in December 2016. The In November 2016, McDonaugh, a purported stockholder, filed a derivative action in the 80th District Court in Harris County, Texas against us, as a nominal defendant, and certain of our current and former officers and directors. The lawsuit alleges that defendants breached their fiduciary duties by failing to maintain adequate internal controls and by permitting or failing to prevent alleged misrepresentations and omissions in our SEC filings and other public disclosures, including in relation to compliance with the FCPA in our Angolan operations and regarding the performance of certain wells offshore Angola. The lawsuit also alleges that defendants received compensation or other benefits in excess of what they were entitled and that certain officers and directors engaged in unlawful trading and misappropriation of information. The lawsuit further alleges that demand was wrongfully refused. The plaintiff asserts claims for breach of fiduciary duty and unjust enrichment and seeks damages in an unspecified amount, reform of our governance and internal controls, restitution and disgorgement of profits, and an award of attorney fees and other costs and expenses. We filed our answer and special exceptions challenging the plaintiff’s standing to bring such claims against us in January 2017. On December 14, 2017, we filed a notice of suggestion on pendency of bankruptcy. The matter remains ongoing. In April 2017, Hafkey, a purported stockholder, filed a derivative action in the 295th District Court in Harris County, Texas against us, as a nominal defendant, and certain of our current and former officers and directors. The lawsuit alleges that current and former officers and directors breached their fiduciary duties by making, and permitting us to make, alleged misrepresentations about two of our exploratory wells offshore Angola; that certain directors caused us to waste corporate assets; and that certain officers received performance–based compensation in excess of what they were entitled. The lawsuit further alleges that demand was wrongfully refused. The plaintiff asserts claims for breach of fiduciary duty, corporate waste, and unjust enrichment and seeks damages in an unspecified amount, disgorgement of profits, appropriate equitable relief, and an award of attorney fees and other costs and expenses. We filed our answer and special exceptions challenging the plaintiff’s standing to bring such claims against us in June 2017. On December 14, 2017, we filed a notice of suggestion on pendency of bankruptcy. The matter remains ongoing. We are vigorously defending against the current derivatives lawsuits and do not believe they will have a material adverse effect on our business. However, we cannot predict the occurrence or outcome of these proceedings with certainty, and if we are unsuccessful in these litigations and any loss exceeds our available insurance, this could have a material adverse effect on our results of operations. In May 2016, we filed suit against XL in Harris County District Court in Houston, Texas. We asserted XL improperly denied coverage for insurance claims made in July 2012 and other claims subsequently submitted to them in connection with our defending against the St. Lucie lawsuit and other investigations and actions. In December 2016, we amended our petition to add Axis, as Axis provided coverage in excess of the XL policy’s limit of liability. We alleged breach of contract, violation of the Texas Prompt Payment of Claims Act, and sought a declaratory judgment that XL and Axis were obligated to pay any additional loss suffered by us due to the circumstances, investigation, and claims described in the suit. In December 2016, we also amended our petition to add claims against Illinois National Insurance Company, an AIG subsidiary (“AIG”), which served as our insurer after XL. Against AIG, we allege breach of contract, violation of the Texas Prompt Payment of Claims Act, violation of the Texas Deceptive Trade Practices-Consumer Protection Act, and seek a declaratory judgment that AIG is obligated to pay any additional loss suffered by us due to the circumstances, investigations, and actions related to the Lontra and/or Loengo wells. In April 2017, we and certain of our current and former officers and directors (the “Intervenors”) settled claims against XL pursuant to which XL paid $11.5 million. In October 2017, we and the Intervenors settled claims against Axis pursuant to which Axis has agreed to pay $6.65 million. We continue to pursue our claims against AIG. The settlement proceeds from XL and Axis are included in “Other income” in our consolidated statements of operations for 2017. Of the $18.2 million, $15.4 million is being held in escrow for the benefit of the insured persons under the XL policy. This restricted cash is included in “Other assets” in our consolidated balance sheets. At December 31, 2017, we had the following estimated contractual commitments for the years ending December 31: Payments Due By Year 2018 2019 2020 2021 2022 Thereafter Social payment obligations (1) $ 86,280 $ — $ — $ — $ — $ — Delay rental payments (2) 3,892 3,506 3,622 3,359 3,036 1,492 Operating leases 2,369 2,405 2,454 2,501 671 — Total $ 92,541 $ 5,911 $ 6,076 $ 5,860 $ 3,707 $ 1,492 (1) Includes our contractual payment obligations for social projects such as the Sonangol Research and Technology Center and academic scholarships for Angolan students that we agreed to pay in consideration for the Angolan government granting us the licenses to explore for and develop hydrocarbons offshore Angola. Provided that Sonangol makes the required payments under the Agreement, these contractual payment obligations will be extinguished. (2) We recorded $6.2million, $9.2 million, and $12.4 million of office and delay rental expense in 2017, 2016 and 2015, respectively.

Equity-Based Compensation

Equity-Based Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity-Based Compensation	NOTE 10. EQUITY–BASED COMPENSATION We have various long–term incentive plans for employees. These plans allow for the issuance of restricted stock awards (“RSAs”), non–qualified stock options (“NQSOs”), performance stock units (“PSUs”), stock appreciation rights (“SARs”) and restricted stock units (“RSUs”). As of December 31, 2017, we have 1.7 million shares authorized for issuance under these plans, and 0.7 million shares remain available for grant. We also have various long–term incentive plans for our non–employee directors. These plans allow for the issuance of NQSOs, RSUs or other equity–based awards as retainers. As of December 31, 2017, we have 0.3 million shares authorized for issuance under these plans, and 0.2 million shares remain available for grant. Our policy is to issue new shares when RSAs are granted, when NQSOs are exercised and, should we elect to settle our PSUs, SARs and RSUs in shares of our common stock, when PSUs, SARs and RSUs are vested. Restricted Stock Awards An RSA is an award of common stock with no exercise price. For RSAs with both a performance and a service condition, we estimated the fair value using the Monte Carlo simulation model. For RSAs with a service condition only, we estimated the fair value using the market price of our common stock on the grant date. RSAs generally vest in three equal annual installments. The following weighted average assumptions were used to estimate the fair value of the RSAs for the year ended December 31: 2016 2015 Expected volatility 55.02 % 49.79 % Risk-free interest rate 2.03 % 1.77 % Dividend yield — % — % Expected life (years) 5.7 10.0 Volatility was estimated based on historical daily prices from January 1, 2010 to the grant date. The risk–free interest rate was based on the yield of a zero–coupon U.S. Treasury bill that is commensurate with the RSAs contractual term. The expected dividend yield was not taken into account as we have historically not paid any dividends. The expected life was based on the derived service period, which is the period between the grant date and the date the performance condition is met, as calculated by the Monte Carlo simulation model. Activity related to RSAs is as follows: Number of RSAs Weighted Average Grant Date Fair Value Per RSA Nonvested at January 1, 2017 408,921 $ 75.29 Vested (170,301 ) 79.07 Forfeited (20,200 ) 152.85 Nonvested at December 31, 2017 218,420 $ 65.95 Exercisable at December 31, 2017 79,140 $ 56.12 The fair value of RSAs granted in 2016 and 2015 was $6.3 million and $30.5 million, respectively, and the fair value of RSAs vested in 2017, 2016 and 2015 was $13.3 million, $4.6 million and $1.4 million, respectively. The weighted average remaining contractual terms for RSAs outstanding and RSAs exercisable at December 31, 2017 were 5.3 years and 4.9 years, respectively. As of December 31, 2017, there was $4.4 million of total unrecognized compensation cost related to unvested RSAs which is expected to be recognized over a weighted-average period of 1.1 years. Non-Qualified Stock Options We grant NQSOs to employees at an exercise price equal to the market value of our common stock on the grant date. The NQSOs have contractual terms of 10 years. We did not grant any NQSOs in 2017. The NQSOs granted in 2016 and 2015 vest after one year of service, subject to our common stock maintaining a minimum stock price for a specified period of time. As the NQSOs granted in 2016 and 2015 had both service and market conditions, we estimated the fair value of these NQSOs using the Monte Carlo simulation model. The following weighted average assumptions were used to estimate the fair value of the NQSOs for the years ended December 31: 2016 2015 Expected volatility 55.02 % 54.97 % Risk-free interest rate 2.03 % 1.84 % Dividend yield — % — % Expected life (years) 5.7 5.5 Volatility was estimated based on historical daily prices from January 1, 2010 to the grant date. The risk–free interest rate was based on the yield of a zero–coupon U.S. Treasury bill that is commensurate with the NQSOs contractual term. The expected dividend yield was not taken into account as we have historically not paid any dividends. The expected life was based on the derived service period, which is the period between the grant date and the date the performance condition is met, as calculated by the Monte Carlo simulation model. As of both December 31, 2017 and 2016, we had 0.3 million NQSOs outstanding and exercisable with a weighted average exercise price of $199.28. No NQSOs were granted or forfeited in 2017. The fair value of NQSOs granted in 2016 and 2015 was $4.0 million and $5.9 million, respectively, and the fair value of NQSOs vested in 2017, 2016 and 2015 was $2.7 million, $14.5 million and $12.3 million, respectively. The weighted average remaining contractual term for both NQSOs outstanding and NQSOs exercisable at December 31, 2017 was 5.7 years. There was no intrinsic value for both NQSOs outstanding and NQSOs exercisable as the exercise price exceeded the market price of our common stock as of December 31, 2017. Performance Stock Units A PSU is an award where each unit represents the right to receive, subject to our common stock attaining a specified return, the value of one share of our common stock at the date of vesting. The PSUs may be settled by, at our discretion, either the issuance of our common stock, cash or a combination thereof based on the fair market value of the common stock on the date of exercise. The PSUs vest in three equal installments subject to our common stock attaining a specified return each vesting date. We estimated the fair value of the PSUs using the Monte Carlo simulation model as the PSUs have both service and performance conditions. The following weighted average assumptions were used to estimate the fair value of the PSUs for the year ended December 31: 2017 2016 Expected volatility 74.79 % 64.31 % Risk-free interest rate 1.47 % 0.80 % Dividend yield — % — % Expected volatility was calculated for the peer company based on historical volatility over the most recent three years using daily stock prices. The risk–free interest rate was based on the yield of a zero–coupon U.S. Treasury bill that is commensurate with the end date of the longest remaining period of three years. The expected dividend yield was not taken into account as we have historically not paid any dividends. Activity related to the PSUs is as follows: Number of PSUs Weighted Average Grant Date Fair Value Per PSU Nonvested at January 1, 2017 18,917 $ 16.97 Granted 442,565 9.75 Forfeited (430,664 ) 9.75 Nonvested at December 31, 2017 30,818 $ 14.18 Exercisable at December 31, 2017 — $ — The fair value of PSUs granted in 2017 and 2016 was $4.3 million and $0.2 million, respectively. The weighted average remaining contractual term for PSUs outstanding at December 31, 2016 was 8.8 years. As of December 31, 2017, there was $0.3 million of total unrecognized compensation cost related to unvested PSUs which is expected to be recognized over a weighted-average period of 2.2 years. Restricted Stock Units An RSU is an award where each unit represents the right to receive the value of one share of our common stock at the date of vesting. RSUs may be settled by, at our discretion, either the issuance of our common stock, cash or a combination thereof based on the fair market value of the common stock on the date of exercise. The RSUs vest in three equal annual installments. Activity related to the RSUs is as follows: Number of RSUs Weighted Average Grant Date Fair Value Per RSU Nonvested at January 1, 2017 162,539 $ 36.60 Granted 674,337 11.17 Vested (70,253 ) 32.75 Forfeited (364,492 ) 12.88 Nonvested at December 31, 2017 402,131 $ 16.13 Exercisable at December 31, 2017 26,526 $ 36.60 The fair value of RSUs granted in 2017 and 2016 was $7.5 million and $8.5 million, respectively. No RSUs were granted in 2015. The fair value of RSUs vested in 2017 and 2016 was $2.3 million and $0.8 million. No RSUs vested in 2015. The weighted average remaining contractual terms for RSUs outstanding and RSUs exercisable at December 31, 2017 was 8.9 years and 8.1 years, respectively. As of December 31, 2017, there was $4.3 million of total unrecognized compensation cost related to unvested RSUs which is expected to be recognized over a weighted–average period of 1.8 years. Stock Appreciation Rights An SAR represents a contractual right to receive an amount equal to the appreciation in the price of one share of our common stock from the grant date over the exercise price of the SAR. SARs may be settled by, at our discretion, either the issuance of our common stock, cash or a combination thereof based on the fair market value of the common stock on the date of exercise. We grant SARs to employees at an exercise price equal to the market value of our common stock on the grant date. The SARs have contractual terms of 10 years and vest in three equal annual installments. We account for the SARs as liability awards, and the fair value of the SARs is remeasured at the end of each reporting period based on the current fair value of the SARs. We estimate the fair value of the SARs using the Black–Scholes option price model. The following weighted average assumptions were used to estimate the fair value of the SARs for the year ended December 31: 2015 Expected volatility 54.97 % Risk-free interest rate 1.84 % Dividend yield — % Expected life (years) 5.5 As of both December 31, 2017 and 2016, we had 0.1 million SARs outstanding and exercisable with a weighted average exercise price of $133.05. No SARs were granted or forfeited in 2017. The weighted average grant date fair value of SARs granted in 2015 was $4.2 million. No SARs were granted in 2017 or 2016. As of December 31, 2017, the weighted average remaining contractual term for both SARs outstanding and SARs exercisable was 7.2 years and there was no intrinsic value for both the SARS outstanding and the SARS exercisable as the exercise price exceeds the market price of our common stock as of December 31, 2017. Non–Employee Director Grants We granted a total of 0.1 million, 0.02 million and 3 thousand shares of our common stock to our non–employee directors as retainer awards in 2017, 2016 and 2015, respectively. The directors have elected to defer the issuance of this stock. Accordingly, we have recorded a liability for the future issuance of these shares. The weighted average fair value of the common stock granted in 2017, 2016 and 2015 was $3.62, $28.34 and $128.97, respectively. In addition, we granted 0.1 million and 0.02 million RSUs to our non–employee directors in 2017 and 2016, respectively. These RSUs will be settled by, at our discretion, either the issuance of our common stock, cash or a combination thereof. The fair value of these RSUs granted in 2017 and 2016 was $1.5 million and $0.8 million, respectively. Settlement of Equity–Based Awards In August 2017, we entered in retention agreements with certain of our officers (see Note 15). Included in these agreements were payments totaling $12.2 million for the repurchase of certain PSUs and RSUs (collectively, the “Awards”) that had been issued to these officers in February 2017. Each of the payments is subject to clawback and repayment by the applicable officer in the event such officer is terminated with cause or resigns without good reason before the one–year anniversary of the agreement. The repurchase of the Awards was accounted for as a modification of the original Awards with a revised service period of 18 months (date of grant through the end of the clawback period). As the Awards were not vested as of the repurchase date, we recognized $9.8 million of equity compensation cost in 2017. This amount corresponds to the percentage of the service period that had been rendered prior to the modification date. The remainder of the equity compensation cost will be recognized over the remaining service period of the Awards. Compensation Cost Equity–based compensation cost is measured at the date of grant based on the calculated fair value of the award and is generally recognized on a straight–line basis over the requisite service period, including those with graded vesting. The compensation cost is determined based on awards ultimately expected to vest, and we have reduced the cost for estimated forfeitures based on historical forfeiture rtes. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods to reflect actual forfeitures. The following table presents the compensation costs recognized for the years ended December 31: 2017 2016 2015 Equity awards $ 11,020 $ 16,243 $ 26,297 Effect of equity award modification 9,843 — — Liability awards (88 ) (1,354 ) 1,451 Total $ 20,775 $ 14,889 $ 27,748

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2017
Compensation And Retirement Disclosure [Abstract]
Employee Benefit Plan	NOTE 11. EMPLOYEE BENEFIT PLAN We have a defined contribution 401(k) plan (the “Plan”). All of our employees are eligible to participate in the Plan after three months of continuous employment. The plan is discretionary and provides a 6% employee contribution match as determined by our Board of Directors. For 2017, 2016 and 2015, we recorded $1.0 million, $1.5 million and $1.7 million, respectively, in benefits contributions to the Plan, which are included in general and administrative expenses in our consolidated statements of operations.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	NOTE 12. INCOME TAXES The provision for income taxes is comprised of the following for the years ended December 31: 2017 2016 2015 Current taxes: U.S. $ — $ — $ — Foreign — — — Deferred taxes: U.S — — — Foreign — — — Total $ — $ — $ — As we establish full valuation allowances against net deferred tax assets where we have determined that it is more likely than not that all of the deferred tax assets will not be realized, we have recognized no income taxes in our consolidated statements of operations for the years ended December 31, 2017, 2016 and 2015. The geographic sources of our loss are as follows for the years ended December 31: 2017 2016 2015 U.S. $ (934,537 ) $ (2,313,482 ) $ (490,190 ) Foreign (33,721 ) (29,827 ) (204,236 ) Net loss $ (968,258 ) $ (2,343,309 ) $ (694,426 ) The effective tax rate on our loss differs from the U.S. statutory rate as follows for the years ended December 31: 2017 2016 2015 Income tax expense (benefit) at the federal statutory rate 35.0 % 35.0 % 35.0 % State income taxes, net of federal income tax benefit 0.1 % 0.1 % 0.1 % Change in federal statutory rate (65.4 )% — % — % Foreign income tax 3.7 % 41.5 % 13.5 % Cancellation of debt (5.7 )% (3.9 )% — % Other (0.2 )% (0.1 )% (0.5 )% Valuation allowance 32.5 % (72.6 )% (48.1 )% Effective rate — % — % — % On December 22, 2017, the Tax Cut and Jobs Act (the “Act”) was enacted into law. Many of the provisions of the Act are effective beginning January 1, 2018, most notable of which is the reduction in the federal corporate statutory rate from 35% to 21%. The changes included in the Act are broad and complex. We are currently in the process of finalizing and quantifying the tax effects of the Act, but have recorded provisional amounts based on reasonable estimates for the measurement and accounting of certain effects of the Act in our consolidated financial statements for 2017. Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. The tax effects of our temporary differences and net operating losses (“NOL”) are as follows at December 31: 2017 2016 Long-term deferred tax asset: Seismic and exploration costs $ 1,753,263 $ 2,227,489 Stock based compensation 11,751 27,342 Domestic NOL carry forwards 481,967 695,434 Foreign NOL carry forwards 26,471 43,969 2019 Notes and 2024 Notes 28,428 — Other 24,919 11,522 Valuation allowance (2,289,519 ) (2,597,708 ) Total long-term deferred tax asset 37,280 408,048 Long-term deferred tax liability: 2019 Notes and 2024 Notes — (169,573 ) Oil and natural gas properties (37,280 ) (238,475 ) Total long-term deferred tax liability (37,280 ) (408,048 ) Net long-term deferred tax asset $ — $ — As of December 31, 2017, we had NOL carryforwards for federal and state income tax purposes of approximately $2,273.0 million and $73.3 million, respectively, which begin to expire in 2026 and 2025, respectively. As of December 31, 2017, we had an NOL carryforward for foreign income tax purposes of approximately $51.3 million which began to expire in 2016. The utilization of the NOL carryforwards is dependent upon generating sufficient future taxable income in the appropriate jurisdictions within the carryforward period. Under the U.S. Internal Revenue Code, our ability to use our NOL carryforwards and other tax attributes may be limited if we experience a change of control, as determined under U.S. Internal Revenue Code. Accordingly, we obtained an order from the Bankruptcy Court that is intended to protect our ability to use our tax attributes by imposing certain notice procedures and transfer restrictions on the trading of our common stock. In general, the order applies to any person or entity that, directly or indirectly, beneficially owns (or would beneficially own as a result of a proposed transfer) at least 4.5% of our common stock. Such persons are required to notify us and the Bankruptcy Court before effecting a transaction that might result in us losing the ability to use our tax attributes, and we have the right to seek an injunction to prevent the transaction if it might adversely affect our ability to use our tax attributes. Any purchase, sale or other transfer of our equity securities in violation of the restrictions of the order is null and would be treated as invalid from the outset as an act in violation of a Bankruptcy Court order and would therefore confer no rights on a proposed transferee. Our tax filings are subject to examination by federal and state tax authorities where we conduct our business. These examinations may result in assessments of additional tax that are resolved with the authorities or through the courts. We have evaluated whether any material tax position we have taken will more likely than not be sustained upon examination by the appropriate taxing authority. As we believe that all such material tax positions we have taken are supportable by existing laws and related interpretations, we believe there are no material uncertain tax positions to consider. There were no unrecognized tax benefits or accrued interest or penalties associated with unrecognized tax benefits as of December 31, 2017 and 2016.

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Share	NOTE 13. EARNINGS PER SHARE A reconciliation of the number of shares used for the basic and diluted loss per share computations is as follows for the years ended December 31: 2017 2016 2015 Weighted average common shares outstanding (basic and diluted) 29,556 27,482 27,320 Anti-dilutive shares excluded from diluted loss per share (1) 4,457 6,904 6,980 (1) Excludes RSAs, RSUs, NQSOs, PSUs, SARs and the shares underlying the 2.625% convertible senior notes due 2019 and the 3.125% convertible senior notes due 2024 as their effect, if included, would have been anti–dilutive.

Other Supplement Information

Other Supplement Information	12 Months Ended
	Dec. 31, 2017
Supplemental Financial Information [Abstract]
Other Supplemental Information	NOTE 14. OTHER SUPPLEMENTAL INFORMATION Cash, cash equivalents and restricted cash are recorded in our consolidated balance sheets as follows as of December 31: 2017 2016 Cash and cash equivalents $ 431,646 $ 613,534 Restricted cash 11,274 2,517 Other assets 15,418 — Cash, cash equivalents and restricted cash $ 458,338 $ 616,051 Supplemental cash flows and noncash transactions were as follows as of and for the years ended December 31: 2017 2016 2015 Supplemental cash flows information: Cash paid for interest $ 142,908 $ 78,320 $ 78,410 Cash paid for income taxes — — — Noncash transactions - changes in accrued capital expenditures (57,824 ) (69,667 ) (47,580 ) Accrued liabilities consisted of the following as of December 31: 2017 2016 Accrued AFE costs $ 1,203 $ 73,808 Social obligation payments 86,280 86,473 Funds from release of letter of credit on Block 9 18,375 18,375 Interest 4,715 13,793 Angolan consumption tax and withholding on services 9,796 9,796 Bonuses 1,522 8,900 General expenses 890 5,849 Seismic and other operating costs 10,996 5,625 Other 3,134 4,799 Total accrued liabilities $ 136,911 $ 227,418

Other Matters

Other Matters	12 Months Ended
	Dec. 31, 2017
Other Matters Disclosure [Abstract]
Other Matters	NOTE 15. OTHER MATTERS In September 2016, we announced that we entered into an amendment to our drilling contract with Rowan (UK) Reliance Limited and recorded a charge of $95.9 million, of which $76.3 million was paid in 2016 and $19.6 million was paid in 2017. This amendment provided for the early termination of our long–term drilling contract for one of their drillships. The drilling contract was originally scheduled to terminate in February 2018, but the amendment provides for a contract termination date in March 2017. This charge is recorded in “Loss on amendment of contract” in our consolidated statements of operations. On March 13, 2017, the SEC informed us that it had initiated an informal inquiry regarding the Sonangol Research and Technology Center (the “SRTC”). As background, in December 2011, we executed the PSC under which we and BP are required to make certain social contributions to Sonangol, including for the SRTC. In March 13, 2017, we also received from the SEC a voluntary request for information regarding such inquiry. We cooperated with the SEC, providing requested information regarding the SRTC. The SEC also asked for, and we provided, information regarding other aspects of our Angolan operations, including two of our wells offshore Angola. On January 29, 2018, the SEC formally concluded its investigation into potential violations of the federal securities laws, including the Foreign Corrupt Practices Act, and advised that the SEC staff did not intend to recommend any enforcement action by the SEC against us. In 2017, we entered into retention agreements with certain of our officers and employees. The retention agreements provided for one–time lump sum payments totaling $19.7 million. Of this amount, $12.2 million was paid to certain officers for the repurchase of the Awards (see Note 10) and $7.5 million was paid as retention bonuses to certain employees. Each of the payments is subject to clawback and repayment by the applicable officer and employee in the event such officer or employee is terminated with cause or resigns without good reason before the one–year anniversary of the agreement. As of December 31, 2017, $11.6 million of these payments, consisting of equity compensation costs of $7.0 million (see Note 10) and compensation expense of $4.6 million, are included in “Other current assets” in our unaudited condensed consolidated balance sheets and will be recognized over the remaining service period. In 2017, $13.4 million of these payments are included in “General and administrative expenses” in our consolidated statements of operations.

Quarterly Data (Unaudited)

Quarterly Data (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Data (Unaudited)	NOTE 16. QUARTERLY DATA (UNAUDITED) First Quarter Second Quarter Third Quarter Fourth Quarter 2017 Revenues $ 9,867 $ 13,749 $ 14,427 $ 15,848 Gross profit (1) 7,169 10,714 11,789 13,153 Net loss (306,255 ) (2) (185,568 ) (149,618 ) (326,817 ) (3) Basic and diluted loss per share $ (10.40 ) $ (6.28 ) $ (5.05 ) $ (11.03 ) 2016 Revenues $ 1,636 $ 3,173 $ 4,228 $ 7,768 Gross profit (1) 680 1,471 1,855 5,225 Net loss (46,615 ) (205,547 ) (218,207 ) (1,872,940 ) (4) Basic and diluted loss per share $ (1.71 ) $ (7.52 ) $ (7.98 ) $ (67.05 ) (1) Represents oil, natural gas and natural gas liquids revenues less lease operating expenses. (2) Includes dry hole costs and impairments of $237.1 million, of which $236.4 million relates to our Shenandoah discovery. (3) Includes reorganization expenses of $332.8 million. (4) Includes dry hole costs and impairments of $1,761.4 million, of which $1,691.8 million relates to our Angolan assets.

Supplementary Information on Oi

Supplementary Information on Oil and Natural Gas Activities (Unaudited)	12 Months Ended
	Dec. 31, 2017
Extractive Industries [Abstract]
Supplementary Information on Oil and Natural Gas Activities (Unaudited)	NOTE 17. SUPPLEMENTARY INFORMATION ON OIL AND NATURAL GAS ACTIVITIES (UNAUDITED) Oil and Natural Gas Properties Capitalized costs relating to oil and natural gas producing activities are as follows at December 31: 2017 2016 Proved oil and natural gas properties $ 127,005 $ 118,245 Unproved oil and natural gas properties, net 850,452 980,844 977,457 1,099,089 Accumulated depreciation, depletion and amortization (60,516 ) (20,204 ) Net capitalized costs $ 916,941 $ 1,078,885 Costs incurred in oil and natural gas property development activities are as follows for the years ended December 31: 2017 2016 2015 Acquisition of unproved oil and natural gas properties $ 1,369 $ 3,715 $ 35,993 Exploration costs: Capitalized 197,096 599,526 718,078 Expensed 47,477 58,170 61,844 Development costs 8,761 39,111 145,021 Total $ 254,703 $ 700,522 $ 960,936 Estimated Proved Oil, Natural Gas and Natural Gas Liquids Reserves Our estimated proved reserves are all located within the U.S. Gulf of Mexico. We caution that there are many uncertainties inherent in estimating proved reserve quantities and in projecting future production rates and the timing of development expenditures. Accordingly, these estimates are expected to change as further information becomes available. Material revisions of reserve estimates may occur in the future, development and production of the oil, natural gas and natural gas liquids reserves may not occur in the periods assumed, and actual prices realized and actual costs incurred may vary significantly from those used in these estimates. The estimates of our proved reserves as of December 31, 2017, 2016 and 2015 have been prepared by Netherland, Sewell & Associates, Inc. (“NSAI”), independent petroleum consultants. The following table sets forth changes in estimated proved and estimated proved developed reserves for the periods indicated. Oil (MMBbls) Natural Gas (Bcf) Natural Gas Liquids (MMBbls) MMBOE Proved developed and undeveloped reserves: As of December 31, 2014 8.4 3.7 — 9.0 Revisions of previous estimates (2.8 ) (1.9 ) 0.3 (2.8 ) As of December 31, 2015 5.6 1.8 0.3 6.2 Revisions of previous estimates (2.2 ) (0.5 ) (0.2 ) (2.5 ) Production (0.4 ) (0.1 ) — (0.4 ) As of December 31, 2016 3.0 1.2 0.1 3.3 Revisions of previous estimates (0.9 ) (0.5 ) — (0.9 ) Production (1.0 ) (0.3 ) (0.1 ) (1.1 ) As of December 31, 2017 1.1 0.4 — 1.3 Proved developed reserves: December 31, 2014 — — — — December 31, 2015 — — — — December 31, 2016 1.9 0.8 0.1 2.1 December 31, 2017 1.1 0.4 — 1.3 Proved undeveloped reserves: December 31, 2014 8.4 3.7 — 9.0 December 31, 2015 5.6 1.8 0.3 6.2 December 31, 2016 1.1 0.4 — 1.2 December 31, 2017 — — — — Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Reserves The following tables present a standardized measure of discounted future net cash flows and changes therein relating to estimated proved oil, natural gas and natural gas liquids reserves. In computing this data, assumptions other than those required by the Securities and Exchange Commission (“SEC”) could produce different results. Accordingly, the data should not be construed as representative of the fair market value of our estimated proved oil, natural gas and natural gas liquids reserves. The following assumptions have been made: • Future cash inflows were based on prices used in estimating our proved oil, natural gas and natural gas liquids reserves. Future price changes were included only to the extent provided by existing contractual agreements. • Future development and production costs were computed using year end costs assuming no change in present economic conditions. • No provisions for future federal income taxes were computed as the tax basis of our oil and natural gas properties in the United States and net operating losses attributable to oil and natural gas operations exceed the future net revenues. • Future net cash flows were discounted at an annual rate of 10%. The standardized measure of discounted future net cash flows relating to estimated proved oil, natural gas and natural gas liquids reserves is as follows at December 31: 2017 2016 2015 Future cash inflows $ 60,665 $ 123,889 $ 288,705 Future production and development costs (48,591 ) (86,103 ) (186,053 ) Future net cash flows 12,074 37,786 102,652 10% annual premium (discount) for estimated timing of cash flows 5,231 1,164 (45,077 ) Standardized measure of discounted future net cash flows $ 17,305 $ 38,950 $ 57,575 As specified by the SEC, the prices for oil, natural gas and natural gas liquids used in this calculation were the average prices during the year determined using the price of the first day of each month, except for volumes subject to fixed price contracts. The prices utilized in calculating our total estimated proved reserves at December 31, 2017, 2016 and 2015 were $51.04, $40.32 and $50.78 per barrel of oil, $31.68, $19.23 and $15.23 per barrel of natural gas liquids, and $2.284, $2.056 and $(0.182) per Mcf of natural gas, respectively. The principal sources of changes in the standardized measure of future net cash flows are as follows for the years ended December 31: 2017 2016 2015 Standardized measure at beginning of year $ 38,950 $ 57,575 $ 365,284 Sales and transfers of oil, natural gas and natural gas liquids produced, net of production costs (42,825 ) (9,231 ) — Net changes in prices and production costs 17,084 (31,738 ) (314,367 ) Development costs incurred during the period 7,589 45,611 — Revisions and other (15,218 ) (23,579 ) (122,584 ) Accretion of discount 3,895 5,757 36,528 Changes in estimated future development costs 7,589 (822 ) 99,964 Changes in timing and other 241 (4,623 ) (7,250 ) Standardized measure, ending $ 17,305 $ 38,950 $ 57,575

Subsequent Events (Unaudited)

Subsequent Events (Unaudited)	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events (Unaudited)	NOTE 18. SUBSEQUENT EVENTS (UNAUDITED) On February 21, 2018, we received the Initial Payment from Sonangol (see Note 3) and (i) notified the relevant ICC arbitral tribunal of the agreement between us and Sonangol to terminate the proceedings related to the joint interest receivable owed to us for operations on Block 21 offshore Angola and (ii) notified the relevant ICC arbitral tribunal of the agreement between us and Sonangol to extend the procedural timetable by an additional four months for the proceedings related to the PSA Arbitration. In accordance with the Agreement, we and Sonangol are finalizing definitive documentation to implement our exit from Angola and to extinguish all debts and obligations of us and Sonangol to each other that have not already been extinguished pursuant to the Agreement. Our claims in the PSA Arbitration will be extinguished upon our receipt of the Final Payment, which is due by July 1, 2018. We evaluated subsequent events for appropriate accounting and disclosure through the date these consolidated financial statements were issued and determined that there were no other material items that required recognition or disclosure in our consolidated financial statements.

Summary of Significant Accoun25

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements include the accounts of the Company and its majority–owned subsidiaries (“we,” “our” or “us”). All significant intercompany accounts and transactions have been eliminated in consolidation. In the Notes to Consolidated Financial Statements, all dollar and share amounts in tabulations are in thousands of dollars and shares, respectively, unless otherwise indicated. On June 16, 2017, we effected a one–for–fifteen reverse stock split of our common stock through an amendment to our second amended and restated certificate of incorporation. As of the effective time of the reverse stock split, every 15 shares of issued and outstanding common stock were converted into one share of common stock, without any change in par value. The amendment to our second amended and restated certificate of incorporation also reduced the number of our authorized shares of common stock from 2.0 billion shares to 133.3 million shares. No fractional shares were issued in connection with the reverse stock split. Instead, each fractional share was rounded up to the nearest whole share of common stock. However, any fractional shares resulting from adjustments to the number of shares underlying stock options and stock appreciation rights were rounded down to the nearest whole share of common stock. All references to shares of common stock, all per share data and all equity compensation activity for all periods presented in the consolidated financial statements and notes to the consolidation financial statements have been adjusted to reflect the reverse stock split on a retroactive basis.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and judgments that affect the reported amounts of assets and liabilities, 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. We base our estimates and judgments on historical experience and on various other assumptions and information that are believed to be reasonable under the circumstances. Estimates and assumptions about future events and their effects cannot be perceived with certainty and, accordingly, these estimates may change as new events occur, as more experience is acquired, as additional information is obtained and as our operating environment changes. While we believe that the estimates and assumptions used in the preparation of the consolidated financial statements are appropriate, actual results could differ from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents We consider all highly liquid investments with an original maturity of three months or less at the time of purchase to be cash equivalents. All of our cash and cash equivalents are maintained with several major financial institutions in the United States. Deposits with these financial institutions may exceed the amount of insurance provided on such deposits; however, we regularly monitor the financial stability of these financial institutions and believe that we are not exposed to any significant default risk.
Restricted Cash	Restricted Cash Our restricted cash is invested in interest–bearing account. As of December 31, 2017, $15.4 million of our restricted cash is being held in escrow for the benefit of the insured persons under our settlements with XL Specialty Insurance Company (“XL”) and Axis Insurance Company (“Axis”). As of December 31, 2017 and 2016, $11.3 million and $2.5 million, respectively, of our restricted cash serves as collateral for certain of our obligations.
Joint Interest and Other Receivables	Joint Interest and Other Receivables Joint interest receivables result from billing shared costs under the respective operating agreements to our partners. Accounts receivable from oil, natural gas and natural gas liquids sales are recorded at the invoiced amount and do not bear interest. We routinely assess the financial strength of our customers and partners and bad debts are recorded based on an account–by–account review after all means of collection have been exhausted, and the potential recovery is considered remote. As of December 31, 2017 and 2016, we did not have any reserves for doubtful accounts. We also did not have any off–balance sheet credit exposure related to our customers.
Investments	Investments As of December 31, 2017, all of our investments in marketable debt securities had matured and were included in “Cash and cash equivalents” in our consolidated balance sheet. Accordingly, there was no potential for other–than-temporary impairments (“OTTI”) as in prior periods. As of December 31, 2016, our investments in marketable debt securities were classified as held–to–maturity as we had the positive intent and ability to hold the investments until they matured. Investments with original maturities of greater than three months and remaining maturities of less than one year were classified as short–term investments. These debt securities were carried at amortized cost and the carrying value of these securities was adjusted for amortization of premiums and accretion of discounts to maturity over the life of the securities. As the estimated fair value of each investment approximates its amortized cost, there were no significant unrecognized holding gains or losses as of December 31, 2016. Income related to these securities was reported as a component of interest income in our consolidated statements of operations. Investments were considered to be impaired when a decline in fair value was determined to be other–than–temporary. We conducted a regular assessment of our debt securities with unrealized losses to determine whether these securities had OTTI. This assessment considered, 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 we intended to sell or whether it was more likely than not that we would be required to sell the debt securities. As of December 31, 2016, we had no OTTI in our debt securities.
Property and Depreciation, Depletion and Amortization	Property and Depreciation, Depletion and Amortization Our oil, natural gas and natural gas liquids producing activities are accounted for under the successful efforts method of accounting. Under this method, costs to drill exploratory wells that do not find proved reserves, geological and geophysical costs and costs of carrying and retaining unproved properties are charged to expense as incurred. For 2017, 2016 and 2015, we recorded dry hole costs and impairments of $282.6 million, $213.5 million and $188.0 million, respectively, to expense costs associated with the drilling of exploratory wells that did not find proved reserves. Costs for unproved leasehold properties and exploratory wells that find reserves that cannot yet be classified as proved are capitalized if the well has found a sufficient quantity of reserves to justify its completion as a producing well and we are making sufficient progress assessing the reserves and the economic and operating viability of the project. Often, the ability to move into the development phase and record proved reserves is dependent on obtaining permits and government or partner approvals, the timing of which is ultimately beyond our control. Exploratory well costs remain suspended as long as we are actively pursuing such approvals and permits, and believe they will be obtained. For complex exploratory projects, it is not unusual to have exploratory wells remain suspended on the balance sheet for several years while additional appraisal drilling and seismic work is performed on the field or while we seek government or partner approval of development plans. Our assessment of suspended exploratory well costs is continuous until a determination is made to either sanction the project or to expense the well costs as dry hole costs as sufficient progress has not been made in assessing the reserves and the economic and operating viability of the project. In 2016, we recorded an impairment charge of dry hole costs of $1,276.4 million to expense costs associated with our Angolan exploratory wells (see Note 3). The capitalized costs of our producing oil and natural gas properties are depreciated and depleted by the units–of–production method based on the ratio of current production to estimated total net proved reserves as estimated by independent petroleum engineers. Proved developed reserves are used in computing unit rates for drilling and development costs and total proved reserves are used for depletion rates of leasehold costs. Other property is stated at cost less accumulated depreciation, which is computed using the straight–line method based on estimated economic lives ranging from three to ten years. We expense costs for maintenance and repairs in the period incurred. Significant improvements and betterments are capitalized if they extend the useful life of the asset.
Impairment of Oil and Natural Gas Properties	Impairment of Oil and Natural Gas Properties We evaluate our proved oil and natural gas properties and related equipment and facilities for impairment whenever events or changes in circumstances indicate that the carrying amounts of such properties may not be recoverable. The determination of recoverability is made based upon estimated undiscounted future net cash flows. The amount of impairment loss, if any, is determined by comparing the fair value, as determined by a discounted cash flow analysis, with the carrying value of the related asset. In 2015, we recorded impairment charges of $256.8 million related to our proved oil and natural gas properties (see Note 5). No impairment charges were recorded in 2017 or 2016 related to our proved oil and natural gas properties. Oil and natural gas leases for unproved properties with a carrying value greater than $1.0 million are assessed individually for impairment based on our current exploration plans and an allowance for impairment is provided if impairment is indicated. Leases that are individually less than $1.0 million in carrying value or are near expiration are amortized over the terms of the leases at rates that provide for full amortization of leases upon lease expiration. These leases have expiration dates ranging from 2018 through 2026. For 2017, 2016 and 2015, we recorded impairment charges of $46.2 million, $66.6 million and $26.9 million, respectively, related to our leases for unproved oil and natural gas properties. In 2016, we also recorded an impairment charge of $353.4 million related to our Angolan leases in conjunction with the write-off of our Angolan exploratory well costs (see Note 3).
Asset Retirement Obligations	Asset Retirement Obligations An asset retirement obligation (“ARO”) represents the future abandonment costs of tangible assets, such as wells, service assets, and other facilities. We record an ARO and capitalize the asset retirement cost in oil and natural gas properties in the period in which the retirement obligation is incurred based upon the fair value of an obligation to perform site reclamation, dismantle facilities or plug and abandon wells. After recording these amounts, the ARO is accreted to its future estimated value using an assumed cost of funds and the additional capitalized costs are depreciated on a unit–of–production basis. If the ARO is settled for an amount other than the recorded amount, a gain or loss is recognized.
Embedded Derivatives	Embedded Derivatives Our first lien senior secured notes due 2021 (the “First Lien Notes”) and our second lien senior secured notes due 2023 (the “Second Lien Notes”) include features which were determined to be embedded derivatives requiring bifurcation and accounting as separate financial instruments. The embedded derivatives were initially recorded at fair value and were subject to remeasurement as of each balance sheet date. We elected not to designate our embedded derivatives as hedging instruments. Changes in the fair value of these embedded derivatives were recorded immediately to earnings in “Loss on derivatives” in our consolidated statements of operations.
Revenue Recognition	Revenue Recognition Oil, natural gas and natural gas liquids revenues are recognized when production is sold to a purchaser at fixed or determinable prices, when delivery has occurred and title has transferred and collectability of the revenue is reasonably assured. We follow the sales method of accounting for natural gas revenues. Under this method of accounting, revenues are recognized based on volumes sold, which may differ from the volume to which we are entitled based on our working interest. An imbalance is recognized as a liability only when the estimated remaining reserves will not be sufficient to enable the under–produced owner(s) to recoup its entitled share through future production. Under the sales method, no receivables are recorded where we have taken less than our share of production. There were no significant natural gas imbalances at December 31, 2017 and 2016.
Income Taxes	Income Taxes We use the liability method to determine our income tax provisions, under which current and deferred tax liabilities and assets are recorded in accordance with enacted tax laws and rates. Under this method, the amounts of deferred tax liabilities and assets at the end of each period are determined using the tax rate expected to be in effect when taxes are actually paid or recovered. Valuation allowances are established to reduce deferred tax assets when it is more likely than not that some portion or all of the deferred tax assets will not be realized.
Concentration of Credit Risk	Concentration of Credit Risk Our oil, natural gas and natural gas liquids revenues are derived principally from uncollateralized sales to customers in the oil and natural gas industry; therefore, our customers may be similarly affected by changes in economic and other conditions within the industry. We have experienced no credit losses on such sales in the past. In 2017 and 2016, one customer accounted for 95.0% and 96.5%, respectively, of our consolidated oil, natural gas and natural gas liquids revenues. We believe that the loss of this customer would have a temporary effect on our revenues but, that over time, we would be able to replace this customer.
Recently Issued Accounting Standards	Recently Issued Accounting Standards In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014–09, Revenue from Contracts with Customers. In February 2016, the FASB issued ASU No. 2016-02, Leases In March 2016, the FASB issued ASU No. 2016-09, Compensation – Stock Compensation No other new accounting pronouncements issued or effective during 2017 have had or are expected to have a material impact on our consolidated financial statements.

Organization and Nature of Bu26

Organization and Nature of Business (Tables)	12 Months Ended
	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Summary of Components of Liabilities Subject to Compromise Included in Consolidated Balance Sheets	The following table summarizes the components of liabilities subject to compromise included in the Company’s consolidated balance sheets as of December 31: 2017 Long-term debt $ 2,939,693 Angolan preliminary consideration 250,000 Accrued interest 25,537 Accrued liabilities 2,249 Trade and other accounts payable 2,858 Total $ 3,220,337
Summary of Components Included in Reorganization Expenses in Consolidated Statements of Operations	The following table summarized the components included in “Reorganization expenses” in the Company’s consolidated statements of operations: 2017 Long-term debt discounts and issuance costs $ 331,822 Advisory and professional fees 950 Total $ 332,772

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Schedule of Fair Value of Held-to-maturity Securities Recorded at Amortized Cost	Our investments in held–to–maturity securities consist of the following as of December 31: 2017 (1) 2016 Corporate securities $ — $ 227,854 Commercial paper — 292,466 U.S. Treasury securities — 161,778 Total $ — $ 682,098 (1)
Schedule of Investments Recorded in Consolidated Balance Sheets	These investments are recorded in our consolidated balance sheets as follows as of December 31: 2017 2016 Cash and cash equivalents $ — $ 341,680 Short-term investments (1) — 340,418 $ — $ 682,098 (1) As of December 31, 2016, $9.1 million of these investments served as collateral for certain of our obligations.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Reconciliation of Changes in the Fair Value of Embedded Derivatives	The reconciliation of changes in the fair value of our embedded derivatives is as follows for the years ended December 31: 2017 2016 Beginning of period $ 50,123 $ — Issuance of First Lien Notes and Second Lien Notes — 47,618 Issuance of additional Second Lien Notes 33,110 — Change in fair value 15,666 2,505 Reclass to long-term debt (98,899 ) — End of period $ — $ 50,123
Fair Value Hierarchy for Liabilities Required to be Measured at Fair Value on a Recurring basis	The following table represents the fair value hierarchy for our liabilities required to be measured at fair value on a recurring basis: Fair Value Measurements at the End of the Reporting Period: Fair Value Level 1 Level 2 Level 3 As of December 31, 2016: Embedded derivative liabilities: First Lien Notes $ 27,012 $ — $ — $ 27,012 Second Lien Notes 23,111 — — 23,111 Total $ 50,123 $ — $ — $ 50,123
Summary of Estimated Fair Value of Long-term Debt	2017 2016 10.75% first lien notes due 2021 Principal outstanding (1) $ 544,444 $ 500,000 Unamortized discount (2) — (34,416 ) Carrying amount 544,444 465,584 7.75% second lien notes due 2023 Principal outstanding (1) 989,187 584,732 Unamortized discount (3) — (54,856 ) Carrying amount 989,187 529,876 2.625% convertible senior notes due 2019: Principal outstanding 619,167 763,446 Unamortized discount and debt issuance costs (4) — (109,689 ) Carrying amount 619,167 653,757 3.125% convertible senior notes due 2024: Principal outstanding 786,895 1,204,145 Unamortized discount and debt issuance costs (5) — (374,013 ) Carrying amount 786,895 830,132 Total debt 2,939,693 2,479,349 Long-term debt subject to compromise (2,939,693 ) — Total long-term debt $ — $ 2,479,349 (1) Includes applicable premiums of $44.4 million for the First Lien Notes and $54.5 million for the Second Lien Notes (see Note 5) (2) (3) (4) (5)
Estimated fair value of long-term debt
Summary of Estimated Fair Value of Long-term Debt	The estimated fair value of our long–term debt is as follows as of December 31: 2017 2016 10.75% first lien notes due 2021 $ 542,500 $ 482,250 7.75% second lien notes due 2023 874,563 327,449 2.625% convertible senior notes due 2019 167,949 305,378 3.125% convertible senior notes due 2024 216,396 332,344 $ 1,801,408 $ 1,447,421

Oil and Natural Gas Properties

Oil and Natural Gas Properties (Tables)	12 Months Ended
	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Schedule of Oil and Natural Gas Properties	Oil and natural gas properties consisted of the following as of December 31: 2017 2016 Proved oil and natural gas properties: Well and development costs $ 127,005 $ 118,245 Accumulated depletion (60,516 ) (20,204 ) Total proved properties 66,489 98,041 Unproved oil and natural gas properties: Oil and natural gas leaseholds 556,771 651,295 Accumulated valuation allowance (457,520 ) (507,198 ) 99,251 144,097 Exploratory wells in process 751,201 836,747 Total unproved properties 850,452 980,844 Total oil and natural gas properties, net $ 916,941 $ 1,078,885
Schedule of Net Changes in Capitalized Exploratory Well Costs	The following tables reflect the net changes in and the cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs): 2017 2016 2015 Beginning of period $ 836,747 $ 1,727,181 $ 1,186,464 Additions to capitalized exploration Exploratory well costs 137,538 499,985 630,395 Capitalized interest 59,558 99,541 87,683 Amounts charged to expense (1) (282,642 ) (1,489,960 ) (177,361 ) End of period $ 751,201 $ 836,747 $ 1,727,181 (1) Amounts represent dry hole costs and impairments related to exploratory wells which did not encounter commercial hydrocarbons or where it was determined that sufficient progress was not being made.
Schedule of Cumulative Costs of Capitalized Exploratory Well Costs	2017 2016 Cumulative costs: Exploratory well costs $ 437,011 $ 582,115 Capitalized interest 314,190 254,632 $ 751,201 $ 836,747 Wells costs capitalized for a period greater than one year after completion after drilling (included in table above) $ 719,639 $ 609,893

Long-term Debt, Net (Tables)

Long-term Debt, Net (Tables)	12 Months Ended
	Dec. 31, 2017
Long Term Debt [Abstract]
Summary of Estimated Fair Value of Long-term Debt	2017 2016 10.75% first lien notes due 2021 Principal outstanding (1) $ 544,444 $ 500,000 Unamortized discount (2) — (34,416 ) Carrying amount 544,444 465,584 7.75% second lien notes due 2023 Principal outstanding (1) 989,187 584,732 Unamortized discount (3) — (54,856 ) Carrying amount 989,187 529,876 2.625% convertible senior notes due 2019: Principal outstanding 619,167 763,446 Unamortized discount and debt issuance costs (4) — (109,689 ) Carrying amount 619,167 653,757 3.125% convertible senior notes due 2024: Principal outstanding 786,895 1,204,145 Unamortized discount and debt issuance costs (5) — (374,013 ) Carrying amount 786,895 830,132 Total debt 2,939,693 2,479,349 Long-term debt subject to compromise (2,939,693 ) — Total long-term debt $ — $ 2,479,349 (1) Includes applicable premiums of $44.4 million for the First Lien Notes and $54.5 million for the Second Lien Notes (see Note 5) (2) (3) (4) (5)
Schedule of Maturities of Long-term Debt	The maturities of our long–term debt are as follows for the years ended December 31: Payments Due By Year 2018 2019 2020 2021 2022 Thereafter Principal outstanding $ 2,939,693 $ — $ — $ — $ — $ —

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2017
Asset Retirement Obligation [Abstract]
Schedule of changes in asset retirement obligation	The changes in ARO are as follows for the years ended December 31: 2017 2016 Beginning of period $ 6,523 $ 3,167 Additions 86 — Revisions (394 ) 2,806 Accretion 1,179 550 End of period $ 7,394 $ 6,523

Commitments and Contingencies

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Schedule of Estimated Contractual Commitments	At December 31, 2017, we had the following estimated contractual commitments for the years ending December 31: Payments Due By Year 2018 2019 2020 2021 2022 Thereafter Social payment obligations (1) $ 86,280 $ — $ — $ — $ — $ — Delay rental payments (2) 3,892 3,506 3,622 3,359 3,036 1,492 Operating leases 2,369 2,405 2,454 2,501 671 — Total $ 92,541 $ 5,911 $ 6,076 $ 5,860 $ 3,707 $ 1,492 (1) Includes our contractual payment obligations for social projects such as the Sonangol Research and Technology Center and academic scholarships for Angolan students that we agreed to pay in consideration for the Angolan government granting us the licenses to explore for and develop hydrocarbons offshore Angola. Provided that Sonangol makes the required payments under the Agreement, these contractual payment obligations will be extinguished. (2)

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Equity Based Compensation
Schedule of Recognized Equity-based Compensation Costs	The following table presents the compensation costs recognized for the years ended December 31: 2017 2016 2015 Equity awards $ 11,020 $ 16,243 $ 26,297 Effect of equity award modification 9,843 — — Liability awards (88 ) (1,354 ) 1,451 Total $ 20,775 $ 14,889 $ 27,748
Restricted stock awards
Equity Based Compensation
Schedule of Weighted Average Assumptions Used to Estimate the Fair Value of Stock Awards	The following weighted average assumptions were used to estimate the fair value of the RSAs for the year ended December 31: 2016 2015 Expected volatility 55.02 % 49.79 % Risk-free interest rate 2.03 % 1.77 % Dividend yield — % — % Expected life (years) 5.7 10.0
Schedule of Activity Related to Stock Awards/Units	Activity related to RSAs is as follows: Number of RSAs Weighted Average Grant Date Fair Value Per RSA Nonvested at January 1, 2017 408,921 $ 75.29 Vested (170,301 ) 79.07 Forfeited (20,200 ) 152.85 Nonvested at December 31, 2017 218,420 $ 65.95 Exercisable at December 31, 2017 79,140 $ 56.12
Non-qualified stock options
Equity Based Compensation
Schedule of Weighted Average Assumptions Used to Estimate the Fair Value of Stock Awards	The following weighted average assumptions were used to estimate the fair value of the NQSOs for the years ended December 31: 2016 2015 Expected volatility 55.02 % 54.97 % Risk-free interest rate 2.03 % 1.84 % Dividend yield — % — % Expected life (years) 5.7 5.5
Performance stock units
Equity Based Compensation
Schedule of Weighted Average Assumptions Used to Estimate Fair Value of Performance Stock Units	2017 2016 Expected volatility 74.79 % 64.31 % Risk-free interest rate 1.47 % 0.80 % Dividend yield — % — %
Schedule of Activity Related to Performance Stock Units	Activity related to the PSUs is as follows: Number of PSUs Weighted Average Grant Date Fair Value Per PSU Nonvested at January 1, 2017 18,917 $ 16.97 Granted 442,565 9.75 Forfeited (430,664 ) 9.75 Nonvested at December 31, 2017 30,818 $ 14.18 Exercisable at December 31, 2017 — $ —
Restricted stock units
Equity Based Compensation
Schedule of Activity Related to Stock Awards/Units	Activity related to the RSUs is as follows: Number of RSUs Weighted Average Grant Date Fair Value Per RSU Nonvested at January 1, 2017 162,539 $ 36.60 Granted 674,337 11.17 Vested (70,253 ) 32.75 Forfeited (364,492 ) 12.88 Nonvested at December 31, 2017 402,131 $ 16.13 Exercisable at December 31, 2017 26,526 $ 36.60
Stock appreciation rights (SARs)
Equity Based Compensation
Schedule of Weighted Average Assumptions Used to Estimate Fair Value of Stock Appreciation Rights	The following weighted average assumptions were used to estimate the fair value of the SARs for the year ended December 31: 2015 Expected volatility 54.97 % Risk-free interest rate 1.84 % Dividend yield — % Expected life (years) 5.5

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Provision for Income Taxes	The provision for income taxes is comprised of the following for the years ended December 31: 2017 2016 2015 Current taxes: U.S. $ — $ — $ — Foreign — — — Deferred taxes: U.S — — — Foreign — — — Total $ — $ — $ —
Schedule of Geographic Sources of Loss	The geographic sources of our loss are as follows for the years ended December 31: 2017 2016 2015 U.S. $ (934,537 ) $ (2,313,482 ) $ (490,190 ) Foreign (33,721 ) (29,827 ) (204,236 ) Net loss $ (968,258 ) $ (2,343,309 ) $ (694,426 )
Schedule of Effective Tax Rate on Loss	The effective tax rate on our loss differs from the U.S. statutory rate as follows for the years ended December 31: 2017 2016 2015 Income tax expense (benefit) at the federal statutory rate 35.0 % 35.0 % 35.0 % State income taxes, net of federal income tax benefit 0.1 % 0.1 % 0.1 % Change in federal statutory rate (65.4 )% — % — % Foreign income tax 3.7 % 41.5 % 13.5 % Cancellation of debt (5.7 )% (3.9 )% — % Other (0.2 )% (0.1 )% (0.5 )% Valuation allowance 32.5 % (72.6 )% (48.1 )% Effective rate — % — % — %
Schedule of Tax Effects of Temporary Differences and Net Operating Losses	The tax effects of our temporary differences and net operating losses (“NOL”) are as follows at December 31: 2017 2016 Long-term deferred tax asset: Seismic and exploration costs $ 1,753,263 $ 2,227,489 Stock based compensation 11,751 27,342 Domestic NOL carry forwards 481,967 695,434 Foreign NOL carry forwards 26,471 43,969 2019 Notes and 2024 Notes 28,428 — Other 24,919 11,522 Valuation allowance (2,289,519 ) (2,597,708 ) Total long-term deferred tax asset 37,280 408,048 Long-term deferred tax liability: 2019 Notes and 2024 Notes — (169,573 ) Oil and natural gas properties (37,280 ) (238,475 ) Total long-term deferred tax liability (37,280 ) (408,048 ) Net long-term deferred tax asset $ — $ —

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted Loss Per Share Computations	A reconciliation of the number of shares used for the basic and diluted loss per share computations is as follows for the years ended December 31: 2017 2016 2015 Weighted average common shares outstanding (basic and diluted) 29,556 27,482 27,320 Anti-dilutive shares excluded from diluted loss per share (1) 4,457 6,904 6,980 (1) Excludes RSAs, RSUs, NQSOs, PSUs, SARs and the shares underlying the 2.625% convertible senior notes due 2019 and the 3.125% convertible senior notes due 2024 as their effect, if included, would have been anti–dilutive.

Other Supplement Information (T

Other Supplement Information (Tables)	12 Months Ended
	Dec. 31, 2017
Supplemental Financial Information [Abstract]
Schedule of Cash, Cash Equivalents and Restricted Cash Recorded in Consolidated Balance Sheets	Cash, cash equivalents and restricted cash are recorded in our consolidated balance sheets as follows as of December 31: 2017 2016 Cash and cash equivalents $ 431,646 $ 613,534 Restricted cash 11,274 2,517 Other assets 15,418 — Cash, cash equivalents and restricted cash $ 458,338 $ 616,051
Schedule of Supplemental Cash Flows and Noncash Transactions	Supplemental cash flows and noncash transactions were as follows as of and for the years ended December 31: 2017 2016 2015 Supplemental cash flows information: Cash paid for interest $ 142,908 $ 78,320 $ 78,410 Cash paid for income taxes — — — Noncash transactions - changes in accrued capital expenditures (57,824 ) (69,667 ) (47,580 )
Schedule of Accrued Liabilities	Accrued liabilities consisted of the following as of December 31: 2017 2016 Accrued AFE costs $ 1,203 $ 73,808 Social obligation payments 86,280 86,473 Funds from release of letter of credit on Block 9 18,375 18,375 Interest 4,715 13,793 Angolan consumption tax and withholding on services 9,796 9,796 Bonuses 1,522 8,900 General expenses 890 5,849 Seismic and other operating costs 10,996 5,625 Other 3,134 4,799 Total accrued liabilities $ 136,911 $ 227,418

Quarterly Data (Unaudited) (Tab

Quarterly Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Data Unaudited	First Quarter Second Quarter Third Quarter Fourth Quarter 2017 Revenues $ 9,867 $ 13,749 $ 14,427 $ 15,848 Gross profit (1) 7,169 10,714 11,789 13,153 Net loss (306,255 ) (2) (185,568 ) (149,618 ) (326,817 ) (3) Basic and diluted loss per share $ (10.40 ) $ (6.28 ) $ (5.05 ) $ (11.03 ) 2016 Revenues $ 1,636 $ 3,173 $ 4,228 $ 7,768 Gross profit (1) 680 1,471 1,855 5,225 Net loss (46,615 ) (205,547 ) (218,207 ) (1,872,940 ) (4) Basic and diluted loss per share $ (1.71 ) $ (7.52 ) $ (7.98 ) $ (67.05 ) (1) Represents oil, natural gas and natural gas liquids revenues less lease operating expenses. (2) Includes dry hole costs and impairments of $237.1 million, of which $236.4 million relates to our Shenandoah discovery. (3) Includes reorganization expenses of $332.8 million. (4) Includes dry hole costs and impairments of $1,761.4 million, of which $1,691.8 million relates to our Angolan assets.

Supplementary Information on 38

Supplementary Information on Oil and Natural Gas Activities (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Extractive Industries [Abstract]
Schedule of Capitalized Costs Relating to Oil and Natural Gas Producing Activities	Capitalized costs relating to oil and natural gas producing activities are as follows at December 31: 2017 2016 Proved oil and natural gas properties $ 127,005 $ 118,245 Unproved oil and natural gas properties, net 850,452 980,844 977,457 1,099,089 Accumulated depreciation, depletion and amortization (60,516 ) (20,204 ) Net capitalized costs $ 916,941 $ 1,078,885
Schedule of Costs Incurred in Oil and Natural Gas Property Development Activities	Costs incurred in oil and natural gas property development activities are as follows for the years ended December 31: 2017 2016 2015 Acquisition of unproved oil and natural gas properties $ 1,369 $ 3,715 $ 35,993 Exploration costs: Capitalized 197,096 599,526 718,078 Expensed 47,477 58,170 61,844 Development costs 8,761 39,111 145,021 Total $ 254,703 $ 700,522 $ 960,936
Schedule of Changes in Estimated Proved and Estimated Proved Developed Reserves	The following table sets forth changes in estimated proved and estimated proved developed reserves for the periods indicated. Oil (MMBbls) Natural Gas (Bcf) Natural Gas Liquids (MMBbls) MMBOE Proved developed and undeveloped reserves: As of December 31, 2014 8.4 3.7 — 9.0 Revisions of previous estimates (2.8 ) (1.9 ) 0.3 (2.8 ) As of December 31, 2015 5.6 1.8 0.3 6.2 Revisions of previous estimates (2.2 ) (0.5 ) (0.2 ) (2.5 ) Production (0.4 ) (0.1 ) — (0.4 ) As of December 31, 2016 3.0 1.2 0.1 3.3 Revisions of previous estimates (0.9 ) (0.5 ) — (0.9 ) Production (1.0 ) (0.3 ) (0.1 ) (1.1 ) As of December 31, 2017 1.1 0.4 — 1.3 Proved developed reserves: December 31, 2014 — — — — December 31, 2015 — — — — December 31, 2016 1.9 0.8 0.1 2.1 December 31, 2017 1.1 0.4 — 1.3 Proved undeveloped reserves: December 31, 2014 8.4 3.7 — 9.0 December 31, 2015 5.6 1.8 0.3 6.2 December 31, 2016 1.1 0.4 — 1.2 December 31, 2017 — — — —
Schedule of Standardized Measure of Discounted Future Net Cash Flows Relating to Estimated Proved Oil, Natural Gas and Natural Gas Liquids Reserves	The standardized measure of discounted future net cash flows relating to estimated proved oil, natural gas and natural gas liquids reserves is as follows at December 31: 2017 2016 2015 Future cash inflows $ 60,665 $ 123,889 $ 288,705 Future production and development costs (48,591 ) (86,103 ) (186,053 ) Future net cash flows 12,074 37,786 102,652 10% annual premium (discount) for estimated timing of cash flows 5,231 1,164 (45,077 ) Standardized measure of discounted future net cash flows $ 17,305 $ 38,950 $ 57,575
Schedule of Changes in Standardized Measure of Future Net Cash Flows	The principal sources of changes in the standardized measure of future net cash flows are as follows for the years ended December 31: 2017 2016 2015 Standardized measure at beginning of year $ 38,950 $ 57,575 $ 365,284 Sales and transfers of oil, natural gas and natural gas liquids produced, net of production costs (42,825 ) (9,231 ) — Net changes in prices and production costs 17,084 (31,738 ) (314,367 ) Development costs incurred during the period 7,589 45,611 — Revisions and other (15,218 ) (23,579 ) (122,584 ) Accretion of discount 3,895 5,757 36,528 Changes in estimated future development costs 7,589 (822 ) 99,964 Changes in timing and other 241 (4,623 ) (7,250 ) Standardized measure, ending $ 17,305 $ 38,950 $ 57,575

Organization and Nature of Bu39

Organization and Nature of Business - Additional Information (Details) $ in Millions	Dec. 21, 2017USD ($)	Dec. 14, 2017	Dec. 31, 2017segment
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of reportable segments | segment			1
Petition date		Dec. 14, 2017
Assets of non-debtor entities of joint interest receivables	$ 163.1
Social obligation payments and Angolan consumption tax and withholding on services	96.1
Non-debtor expenses of dry hole costs and impairments related to exploratory well and leaseholds	$ 45.3

Organization and Nature of Bu40

Organization and Nature of Business - Summary of Components of Liabilities Subject to Compromise Included in Consolidated Balance Sheets (Details) $ in Thousands	Dec. 31, 2017USD ($)
Liabilities Subject To Compromise [Abstract]
Long-term debt	$ 2,939,693
Angolan preliminary consideration	250,000
Accrued interest	25,537
Accrued liabilities	2,249
Trade and other accounts payable	2,858
Total	$ 3,220,337

Organization and Nature of Bu41

Organization and Nature of Business - Summary of Components Included in Reorganization Expenses in Consolidated Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017
Reorganization Items [Abstract]
Long-term debt discounts and issuance costs		$ 331,822
Advisory and professional fees		950
Total	$ 332,800	$ 332,772

Summary of Significant Accoun42

Summary of Significant Accounting Policies - Additional Information (Details)	Jun. 16, 2017shares	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)Customershares	Dec. 31, 2016USD ($)Customershares	Dec. 31, 2015USD ($)	Jun. 15, 2017shares	Jan. 01, 2017USD ($)	Dec. 31, 2014USD ($)
Summary Of Significant Accounting Policies [Line Items]
Description of revers stock split	On June 16, 2017, we effected a one–for–fifteen reverse stock split of our common stock through an amendment to our second amended and restated certificate of incorporation. As of the effective time of the reverse stock split, every 15 shares of issued and outstanding common stock were converted into one share of common stock, without any change in par value.
Stock split ratio	0.067
Common stock, shares authorized | shares	133,300,000		133,333,333	133,333,333		2,000,000,000
Fractional shares issued in reverse stock split | shares	0
Restricted cash			$ 11,274,000	$ 2,517,000
Held-to-maturity securities unrecognized holding gains				0
Held-to-maturity securities unrecognized holding losses				0
OTTI in debt securities				0
Dry hole and impairment costs			282,600,000	213,500,000	$ 188,000,000
Upper limit of individual leasehold			1,000,000
Lower limit of individual leasehold			$ 1,000,000
Leases expiration dates, description			These leases have expiration dates ranging from 2018 through 2026.
Cumulative effect of change in accounting for equity based compensation			$ (1,793,948,000)	(841,334,000)	1,446,137,000			$ 2,114,266,000
Accounting Standards Update 2016-09
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect adjustment for previously unrecognized excess tax benefits		$ 0
Additional Paid-in Capital
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of change in accounting for equity based compensation			4,239,746,000	4,223,729,000	4,167,913,000			4,141,616,000
Additional Paid-in Capital | Accounting Standards Update 2016-09
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of change in accounting for equity based compensation				375,000			$ 400,000
Accumulated Deficit
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of change in accounting for equity based compensation			$ (6,033,990,000)	(5,065,357,000)	(2,722,048,000)			$ (2,027,622,000)
Accumulated Deficit | Accounting Standards Update 2016-09
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of change in accounting for equity based compensation				$ (375,000)			$ (400,000)
Sales revenue, net | Customer concentration risk
Summary Of Significant Accounting Policies [Line Items]
Number of customers | Customer			1	1
Concentration risk, percentage			95.00%	96.50%
7.75% Second Lien Notes due 2023
Summary Of Significant Accounting Policies [Line Items]
Debt instrument maturity year			2,023
Minimum
Summary Of Significant Accounting Policies [Line Items]
Estimated economic lives			3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Estimated economic lives			10 years
Proved oil and natural gas properties
Summary Of Significant Accounting Policies [Line Items]
Impairment charges			$ 0	$ 0	256,800,000
Unproved oil and natural gas properties
Summary Of Significant Accounting Policies [Line Items]
Impairment charges			46,200,000	66,600,000	$ 26,900,000
Angolan | Exploration well costs
Summary Of Significant Accounting Policies [Line Items]
Impairment charge of dry hole costs				1,276,400,000
Impairment charges				$ 353,400,000
XL Specialty Insurance Company and Axis Insurance Company [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash			$ 15,400,000

Angola Settlement - Additional

Angola Settlement - Additional Information (Details) - USD ($) $ in Millions	Dec. 19, 2017	Jul. 17, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Aug. 31, 2015
Sonangol
Loss Contingencies [Line Items]
Claims settlement amount			$ 2,000
Claims settlement amount		$ 250
Block 20, offshore Angola | CIE Angola Block 20 Ltd
Loss Contingencies [Line Items]
Percentage of working interest acquired						40.00%
Block 21, offshore Angola | Sonangol P&P
Loss Contingencies [Line Items]
Claims settlement amount			$ 162
Block 21, offshore Angola | CIE Angola Block 21 Ltd
Loss Contingencies [Line Items]
Percentage of working interest acquired						40.00%
Block 20 and Block 21 | Sonangol and Sonangol P&P
Loss Contingencies [Line Items]
Claims settlement amount	$ 500
Claims settlement initial payment amount from other party	150
Claims settlement final payment amount from other party	$ 350
Description of settlement agreement				On December 19, 2017, certain of our subsidiaries executed a settlement agreement (the “Agreement”) with Sonangol and Sonangol P&P to resolve all disputes and transition our interests in Blocks 20 and 21 offshore Angola to Sonangol for $500.0 million. Pursuant to the Agreement, Sonangol is required to pay an initial non–refundable payment of $150.0 million on or before February 23, 2018 (the “Initial Payment”) and the final payment of $350.0 million on or before July 1, 2018 (the “Final Payment”). On January 25, 2018, the Bankruptcy Court entered an Order Approving Debtors’ Motion for Entry of an Order (I) Authorizing Performance Under Settlement Agreement, (II) Approving Settlement Agreement, and (III) Granting Related Relief [Docket No. 127] authorizing the Debtors’ entry into the Agreement subject to the terms and conditions set forth therein. The Agreement remains subject to the review of the Bankruptcy Court.
Block 20 and Block 21 | CIE Angola block 20 and block 21
Loss Contingencies [Line Items]
Impairment charges					$ 62
Block 20 and Block 21 | CIE Angola block 20 and block 21 | Angolan
Loss Contingencies [Line Items]
Impairment charges					$ 1,629.8

Investments - Schedule of Fair

Investments - Schedule of Fair Value of Held-to-maturity Securities Recorded at Amortized Cost (Details) $ in Thousands	Dec. 31, 2016USD ($)
Schedule Of Held To Maturity Securities [Line Items]
Fair market value, Current	$ 682,098
Corporate securities
Schedule Of Held To Maturity Securities [Line Items]
Fair market value, Current	227,854
U.S. Treasury securities
Schedule Of Held To Maturity Securities [Line Items]
Fair market value, Current	161,778
Commercial paper
Schedule Of Held To Maturity Securities [Line Items]
Fair market value, Current	$ 292,466

Investments - Schedule of Inves

Investments - Schedule of Investments Recorded in Consolidated Balance Sheets (Details) $ in Thousands	Dec. 31, 2016USD ($)
Schedule Of Held To Maturity Securities [Line Items]
Fair market value	$ 682,098
Cash and cash equivalents
Schedule Of Held To Maturity Securities [Line Items]
Fair market value	341,680
Short-term investments
Schedule Of Held To Maturity Securities [Line Items]
Fair market value	$ 340,418

Investments - Schedule of Inv46

Investments - Schedule of Investments Recorded in Consolidated Balance Sheets (Parenthetical) (Details) $ in Millions	Dec. 31, 2016USD ($)
Short-term investments
Schedule Of Held To Maturity Securities [Line Items]
Investments served as collateral for certain obligations	$ 9.1

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Pre tax impairment of oil and gas properties			$ 256,800,000
Fair value of proved oil and gas properties			$ 68,400,000
Held-to-maturity securities unrecognized holding gains	$ 0
Held-to-maturity securities unrecognized holding losses	$ 0
First Lien Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Applicable premiums due		$ 44,400,000
Second Lien Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Applicable premiums due		54,500,000
Liabilities Subject to Compromise | First Lien Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Applicable premiums due		44,400,000
Liabilities Subject to Compromise | Second Lien Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Applicable premiums due		$ 54,500,000

Fair Value Measurements - Recon

Fair Value Measurements - Reconciliation of Changes in the Fair Value of Embedded Derivatives (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Embedded Derivative [Abstract]
Beginning of period	$ 50,123
Issuance of First Lien Notes and Second Lien Notes		$ 47,618
Issuance of additional Second Lien Notes	33,110
Change in fair value	15,666	2,505
Reclass to long-term debt	$ (98,899)
End of period		$ 50,123

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value Hierarchy for Liabilities Required to be Measured at Fair Value on a Recurring basis (Details) $ in Thousands	Dec. 31, 2016USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Embedded derivative liabilities, Fair Value	$ 50,123
Recurring basis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Embedded derivative liabilities, Fair Value	50,123
Recurring basis | First Lien Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Embedded derivative liabilities, Fair Value	27,012
Recurring basis | Second Lien Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Embedded derivative liabilities, Fair Value	23,111
Level 3 | Recurring basis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Embedded derivative liabilities, Fair Value	50,123
Level 3 | Recurring basis | First Lien Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Embedded derivative liabilities, Fair Value	27,012
Level 3 | Recurring basis | Second Lien Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Embedded derivative liabilities, Fair Value	$ 23,111

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Estimated Fair Value of Long-term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, fair value	$ 1,801,408	$ 1,447,421
10.75% first lien notes due 2021
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, fair value	542,500	482,250
7.75% second lien notes due 2023
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, fair value	874,563	327,449
2.625% convertible senior notes due 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, fair value	167,949	305,378
3.125% convertible senior notes due 2024
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, fair value	$ 216,396	$ 332,344

Fair Value Measurements - Sum51

Fair Value Measurements - Summary of Estimated Fair Value of Long-term Debt (Parenthetical) (Details)	Dec. 31, 2017	Dec. 06, 2016
10.75% first lien notes due 2021
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate (as a percent)	10.75%	10.75%
7.75% second lien notes due 2023
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate (as a percent)	7.75%	7.75%
2.625% convertible senior notes due 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate (as a percent)	2.625%	2.625%
3.125% convertible senior notes due 2024
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate (as a percent)	3.125%	3.125%

Oil and Natural Gas Propertie52

Oil and Natural Gas Properties - Schedule of Oil and Natural Gas Properties (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property Plant And Equipment [Abstract]
Well and development costs	$ 127,005	$ 118,245
Accumulated depletion	(60,516)	(20,204)
Total proved properties	66,489	98,041
Oil and natural gas leaseholds	556,771	651,295
Accumulated valuation allowance	(457,520)	(507,198)
Total oil and gas leasehold	99,251	144,097
Exploratory wells in process	751,201	836,747	$ 1,727,181	$ 1,186,464
Total unproved properties	850,452	980,844
Total oil and natural gas properties, net	$ 916,941	$ 1,078,885

Oil and Natural Gas Propertie53

Oil and Natural Gas Properties - Schedule of Net Changes in Capitalized Exploratory Well Costs (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net changes in capitalized exploratory well costs (excluding any related leasehold costs)
Beginning of period		$ 836,747	$ 1,727,181	$ 1,186,464
Amounts charged to expense	[1]	(282,642)	(1,489,960)	(177,361)
End of period		751,201	836,747	1,727,181
Exploration well costs
Net changes in capitalized exploratory well costs (excluding any related leasehold costs)
Beginning of period		582,115
Additions to capitalized exploration		137,538	499,985	630,395
End of period		437,011	582,115
Capitalized interest
Net changes in capitalized exploratory well costs (excluding any related leasehold costs)
Beginning of period		254,632
Additions to capitalized exploration		59,558	99,541	$ 87,683
End of period		$ 314,190	$ 254,632
[1]	Amounts represent dry hole costs and impairments related to exploratory wells which did not encounter commercial hydrocarbons or where it was determined that sufficient progress was not being made.

Oil and Natural Gas Propertie54

Oil and Natural Gas Properties - Schedule of Cumulative Costs of Capitalized Exploratory Well Costs (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs)
Cumulative costs	$ 751,201	$ 836,747	$ 1,727,181	$ 1,186,464
Well costs capitalized for a period greater than one year after completion of drilling	719,639	609,893
Exploration well costs
Cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs)
Cumulative costs	437,011	582,115
Capitalized interest
Cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs)
Cumulative costs	$ 314,190	$ 254,632

Long-term Debt, Net - Schedule

Long-term Debt, Net - Schedule of Long-term Debt, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt instrument
Total debt	$ 2,939,693	$ 2,479,349
Long-term debt subject to compromise	(2,939,693)
Long-term debt		2,479,349
10.75% first lien notes due 2021
Debt instrument
Principal outstanding	544,444	500,000
Unamortized discount		(34,416)
Carrying amount	544,444	465,584
7.75% second lien notes due 2023
Debt instrument
Principal outstanding	989,187	584,732
Unamortized discount		(54,856)
Carrying amount	989,187	529,876
2.625% convertible senior notes due 2019
Debt instrument
Principal outstanding	619,167	763,446
Unamortized discount and debt issuance costs		(109,689)
Carrying amount	619,167	653,757
3.125% convertible senior notes due 2024
Debt instrument
Principal outstanding	786,895	1,204,145
Unamortized discount and debt issuance costs		(374,013)
Carrying amount	$ 786,895	$ 830,132

Long-term Debt, Net - Schedul56

Long-term Debt, Net - Schedule of Long-term Debt, Net (Parenthetical) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
First Lien Notes
Debt instrument
Applicable premiums due	$ 44.4
Second Lien Notes
Debt instrument
Applicable premiums due	$ 54.5
10.75% first lien notes due 2021
Debt instrument
Effective interest rate	12.60%	12.60%
7.75% second lien notes due 2023
Debt instrument
Effective interest rate	9.60%	9.60%
2.625% convertible senior notes due 2019
Debt instrument
Effective interest rate	8.40%	8.40%
3.125% convertible senior notes due 2024
Debt instrument
Effective interest rate	9.00%	9.00%

Long-term Debt, Net - Additiona

Long-term Debt, Net - Additional Information (Details) $ / shares in Units, shares in Millions	Dec. 01, 2017USD ($)	Nov. 15, 2017USD ($)	Dec. 06, 2016USD ($)shares	May 13, 2014USD ($)$ / shares	Dec. 17, 2012USD ($)$ / shares	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 13, 2017USD ($)	Dec. 31, 2015USD ($)
Debt instrument
Debt instrument unpaid accrued interest						$ 2,939,693,000
Notes
Debt instrument
Repurchase price as a percentage of principal amount of debt instrument				100.00%	100.00%
2.625% convertible senior notes due 2019
Debt instrument
Interest rate (as a percent)			2.625%			2.625%
Aggregate principal amount of notes issued			$ 616,600,000			$ 144,300,000
Debt conversion, common stock shares issued | shares			30
Debt instrument maturity date						Dec. 1, 2019
Debt instrument payment terms						Interest is payable semi–annually in arrears on June 1 and December 1 of each year.
Initial conversion rate of common stock					1.8682
Initial conversion price per share of common stock (in dollars per share) | $ / shares					$ 535.20
Carrying amount of the equity components					$ 381,400,000
Debt issue cost allocated to the equity component					$ 9,100,000
2.625% convertible senior notes due 2019 | Liabilities Subject to Compromise
Debt instrument
Debt instrument unamortized discount						$ 58,300,000
Debt instrument unpaid accrued interest								$ 8,700,000
Interest expense recognized	$ 0					0
Unrecognized contractual interest expense	800,000
Debt issuance costs						$ 3,900,000
Liabilities subject to compromise deferred interest payment	$ 8,100,000
3.125% convertible senior notes due 2024
Debt instrument
Interest rate (as a percent)			3.125%			3.125%
Aggregate principal amount of notes issued			$ 95,900,000			$ 417,200,000
Debt instrument maturity date						May 15, 2024
Debt instrument payment terms						Interest is payable semi–annually in arrears on May 15 and November 15 of each year.
Initial conversion rate of common stock				2.8907
Initial conversion price per share of common stock (in dollars per share) | $ / shares				$ 345.90
Carrying amount of the equity components				$ 464,700,000
Debt issue cost allocated to the equity component				$ 11,100,000
3.125% convertible senior notes due 2024 | Liabilities Subject to Compromise
Debt instrument
Debt instrument unamortized discount						$ 211,500,000
Debt instrument unpaid accrued interest								$ 14,200,000
Interest expense recognized		$ 0
Unrecognized contractual interest expense		1,200,000
Debt issuance costs						$ 9,400,000
Liabilities subject to compromise deferred interest payment		$ 12,300,000
10.75% first lien notes
Debt instrument
Interest rate (as a percent)			10.75%			10.75%
Aggregate principal amount of notes issued			$ 500,000,000
Percentage of aggregate principal amount for cash			98.00%
Derivative liabilities			$ 24,800,000
Debt instrument maturity date						Dec. 6, 2021
Debt instrument payment terms						Interest is payable semi–annually in arrears on each June 1 and December 1 of each year.
Debt instrument unamortized discount							$ 34,416,000
10.75% first lien notes | Liabilities Subject to Compromise
Debt instrument
Debt instrument unamortized discount						$ 29,300,000
10.75% first lien notes | Cobalt International Energy Overseas Ltd
Debt instrument
Percentage of debt secured guaranteed			65.00%
7.75% Second Lien Notes due 2023
Debt instrument
Interest rate (as a percent)			7.75%			7.75%
Aggregate principal amount of notes issued			$ 584,700,000			$ 350,000,000
Derivative liabilities			22,800,000			$ 33,100,000
Debt instrument maturity date						Dec. 1, 2023
Debt instrument payment terms						Interest is payable semi–annually in arrears on each June 1 and December 1 of each year
Debt instrument unamortized discount							54,856,000
7.75% Second Lien Notes due 2023 | Liabilities Subject to Compromise
Debt instrument
Debt instrument unamortized discount						$ 19,400,000
Debt instrument unpaid accrued interest						2,600,000
Interest expense recognized						0
Unrecognized contractual interest expense						3,400,000
Facility Agreement
Debt instrument
Amount outstanding							0
Facility Agreement | GOM#1
Debt instrument
Maximum borrowing capacity									$ 150,000,000
Write off of debt issuance cost							$ 3,300,000
General and administrative expenses
Debt instrument
Transaction related costs			$ 19,600,000			$ 3,000,000
First Lien Notes
Debt instrument
Adequate protection payments at default interest rate								11.75%

Long-term Debt, Net - Schedul58

Long-term Debt, Net - Schedule of Maturities of Long-term Debt (Details) $ in Thousands	Dec. 31, 2017USD ($)
Maturities Of Long Term Debt [Abstract]
Principal outstanding, 2018	$ 2,939,693

Asset Retirement Obligations -

Asset Retirement Obligations - Schedule of Changes in Asset Retirement Obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Changes in asset retirement obligation
Beginning of period	$ 6,523	$ 3,167
Additions	86
Revisions	(394)	2,806
Accretion	1,179	550
End of period	$ 7,394	$ 6,523

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Thousands	Nov. 30, 2014Stockholder	Oct. 31, 2017USD ($)	Apr. 30, 2017USD ($)Well	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	May 31, 2016Well
Commitments And Contingencies [Line Items]
Number of purported stockholders | Stockholder	2
Number of exploration wells | Well			2				2
Office and delay rental expense				$ 6,200	$ 9,200	$ 12,400
Claims against XL Specialty Insurance Company
Commitments And Contingencies [Line Items]
Claims settlement amount			$ 11,500
Claims against XL Specialty Insurance Company | Other Assets
Commitments And Contingencies [Line Items]
Restricted cash				15,400
Claims against XL Specialty Insurance Company | Other Income
Commitments And Contingencies [Line Items]
Claims settlement amount				$ 18,200
Axis Insurance Company
Commitments And Contingencies [Line Items]
Claims settlement amount		$ 6,650
Ongoing Matter | Nueman Lawsuit With The St. Lucie Lawsuit
Commitments And Contingencies [Line Items]
Interlocutory appeal filed date				October 10, 2017

Commitments and Contingencies61

Commitments and Contingencies - Schedule of Estimated Contractual Commitments (Details) $ in Thousands	Dec. 31, 2017USD ($)
Contractual obligation and commitments
2,018	$ 92,541
2,019	5,911
2,020	6,076
2,021	5,860
2,022	3,707
Thereafter	1,492
Social Payment Obligations
Contractual obligation and commitments
2,018	86,280
Delay Rental Payments
Contractual obligation and commitments
2,018	3,892
2,019	3,506
2,020	3,622
2,021	3,359
2,022	3,036
Thereafter	1,492
Operating Leases
Contractual obligation and commitments
2,018	2,369
2,019	2,405
2,020	2,454
2,021	2,501
2,022	$ 671

Equity-Based Compensation - Add

Equity-Based Compensation - Additional Information (Details)	1 Months Ended	12 Months Ended
	Aug. 31, 2017USD ($)shares	Dec. 31, 2017USD ($)Installment$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares
Equity Based Compensation
Shares available for grant under the plan		700,000
Shares authorized under the plan		1,700,000
Contractual term for options granted		10 years
Vesting service period			1 year	1 year
Recognized equity compensation cost | $		$ 9,843,000
Restricted stock awards
Equity Based Compensation
Number of equal vesting installments | Installment		3
Fair value granted | $			$ 6,300,000	$ 30,500,000
Fair value vested | $		$ 13,300,000	$ 4,600,000	1,400,000
Weighted average remaining contractual terms for options outstanding		5 years 3 months 18 days
Weighted average remaining contractual terms for options exercisable		4 years 10 months 24 days
Unrecognized compensation cost | $		$ 4,400,000
Period for recognition of unrecognized compensation cost		1 year 1 month 6 days
Vested, Shares		170,301
Vested (in dollars per share) | $ / shares		$ 79.07
Options outstanding		218,420	408,921
Weighted average exercise price outstanding | $ / shares		$ 65.95	$ 75.29
Non-qualified stock options
Equity Based Compensation
Weighted average remaining contractual terms for options outstanding		5 years 8 months 12 days
Weighted average remaining contractual terms for options exercisable		5 years 8 months 12 days
Options granted		0
Options forfeited		0
Options outstanding		300,000	300,000
Options exercisable		300,000	300,000
Weighted average exercise price outstanding | $ / shares		$ 199.28	$ 199.28
Weighted average exercise price exercisable | $ / shares		$ 199.28	$ 199.28
Fair value granted | $			$ 4,000,000	5,900,000
Fair value vested | $		$ 2,700,000	$ 14,500,000	12,300,000
Intrinsic value, outstanding | $		0
Intrinsic value, exercisable | $		$ 0
Performance stock units
Equity Based Compensation
Number of equal vesting installments | Installment		3
Weighted average remaining contractual terms for options outstanding			8 years 9 months 18 days
Unrecognized compensation cost | $		$ 300,000
Period for recognition of unrecognized compensation cost		2 years 2 months 12 days
Grant date fair value | $		$ 4,300,000	$ 200,000
Options outstanding		30,818	18,917
Weighted average exercise price outstanding | $ / shares		$ 14.18	$ 16.97
Granted (in shares)		442,565
Weighted average fair value granted | $ / shares		$ 9.75
Restricted stock units
Equity Based Compensation
Number of equal vesting installments | Installment		3
Fair value vested | $		$ 2,300,000	$ 800,000
Weighted average remaining contractual terms for options outstanding		8 years 10 months 24 days
Weighted average remaining contractual terms for options exercisable		8 years 1 month 6 days
Unrecognized compensation cost | $		$ 4,300,000
Period for recognition of unrecognized compensation cost		1 year 9 months 18 days
Grant date fair value | $		$ 7,500,000	$ 8,500,000	$ 0
Vested, Shares		70,253		0
Vested (in dollars per share) | $ / shares		$ 32.75
Options outstanding		402,131	162,539
Weighted average exercise price outstanding | $ / shares		$ 16.13	$ 36.60
Granted (in shares)		674,337
Weighted average fair value granted | $ / shares		$ 11.17
Stock appreciation rights (SARs)
Equity Based Compensation
Number of equal vesting installments | Installment		3
Weighted average remaining contractual terms for options outstanding		7 years 2 months 12 days
Weighted average remaining contractual terms for options exercisable		7 years 2 months 12 days
Options exercisable		0.1	0.1
Weighted average exercise price exercisable | $ / shares		$ 133.05	$ 133.05
Intrinsic value, outstanding | $		$ 0
Intrinsic value, exercisable | $		$ 0
Non-option granted		0
Non-option forfeited		0
Options outstanding		0.1	0.1
Weighted average exercise price outstanding | $ / shares		$ 133.05	$ 133.05
Weighted average grant date fair value | $				$ 4,200,000
Granted (in shares)		0	0
Performance stock units and Restricted stock units
Equity Based Compensation
Vested, Shares	0
Repayments of equity based awards | $	$ 12,200,000
Repurchase of awards revised service period	18 months
Recognized equity compensation cost | $		$ 9,800,000
Non-employee director grants
Equity Based Compensation
Shares available for grant under the plan		200,000
Shares authorized under the plan		300,000
Non-employee director grants | Restricted stock units
Equity Based Compensation
Grant date fair value | $		$ 1,500,000	$ 800,000
Granted (in shares)		100,000	20,000
Non-employee director grants | Retainer awards | Common Stock
Equity Based Compensation
Granted (in shares)		100,000	20,000	3,000
Weighted average fair value granted | $ / shares		$ 3.62	$ 28.34	$ 128.97

Equity-Based Compensation - Sch

Equity-Based Compensation - Schedule of Weighted Average Assumptions Used to Estimate the Fair Value of Stock Awards (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted stock awards
Assumptions used to determine the fair value of stock award granted
Expected volatility	55.02%	49.79%
Risk-free interest rate	2.03%	1.77%
Dividend yield	0.00%	0.00%
Expected life (years)	5 years 8 months 12 days	10 years
Non-qualified stock options
Assumptions used to determine the fair value of stock award granted
Expected volatility		55.02%	54.97%
Risk-free interest rate		2.03%	1.84%
Dividend yield		0.00%	0.00%
Expected life (years)		5 years 8 months 12 days	5 years 6 months

Equity-Based Compensation - S64

Equity-Based Compensation - Schedule of Activity Related to Restricted Stock Awards/Units (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2015
Restricted stock awards
Number of Shares
Nonvested at the beginning of the period (in shares)	408,921
Vested (in shares)	(170,301)
Forfeited (in shares)	(20,200)
Nonvested at the end of the period (in shares)	218,420
Exercisable at the end of the period (in shares)	79,140
Weighted Average Grant Date Fair Value Per Share
Nonvested at the beginning of the period (in dollars per share)	$ 75.29
Vested (in dollars per share)	79.07
Forfeited (in dollars per share)	152.85
Nonvested at the end of the period (in dollars per share)	65.95
Exercisable at the end of the period (in dollars per share	$ 56.12
Restricted stock units
Number of Shares
Nonvested at the beginning of the period (in shares)	162,539
Granted (in shares)	674,337
Vested (in shares)	(70,253)	0
Forfeited (in shares)	(364,492)
Nonvested at the end of the period (in shares)	402,131
Exercisable at the end of the period (in shares)	26,526
Weighted Average Grant Date Fair Value Per Share
Nonvested at the beginning of the period (in dollars per share)	$ 36.60
Granted (in dollars per share)	11.17
Vested (in dollars per share)	32.75
Forfeited (in dollars per share)	12.88
Nonvested at the end of the period (in dollars per share)	16.13
Exercisable at the end of the period (in dollars per share	$ 36.60

Equity-Based Compensation - S65

Equity-Based Compensation - Schedule of Weighted Average Assumptions Used to Estimate Fair Value of Performance Stock Units (Details) - Performance stock units	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Assumptions used to determine the fair value of stock award granted
Expected volatility	74.79%	64.31%
Risk-free interest rate	1.47%	0.80%

Equity-Based Compensation - S66

Equity-Based Compensation - Schedule of Activity Related to Performance Stock Units (Details) - Performance stock units	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Number of Shares
Nonvested at the beginning of the period (in shares) | shares	18,917
Granted (in shares) | shares	442,565
Forfeited (in shares) | shares	(430,664)
Nonvested at the end of the period (in shares) | shares	30,818
Weighted Average Grant Date Fair Value Per Share
Nonvested at the beginning of the period (in dollars per share) | $ / shares	$ 16.97
Granted (in dollars per share) | $ / shares	9.75
Forfeited (in dollars per share) | $ / shares	9.75
Nonvested at the end of the period (in dollars per share) | $ / shares	$ 14.18

Equity-Based Compensation - S67

Equity-Based Compensation - Schedule Weighted Average Assumptions Used to Estimate Fair Value of Stock Appreciation Rights (Details) - Stock appreciation rights (SARs)	12 Months Ended
	Dec. 31, 2015
Assumptions used to determine the fair value of stock award granted
Expected volatility	54.97%
Risk-free interest rate	1.84%
Dividend yield	0.00%
Expected life (years)	5 years 6 months

Equity-Based Compensation - S68

Equity-Based Compensation - Schedule of Recognized Equity-based Compensation Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity Based Compensation
Compensation costs	$ 20,775	$ 14,889	$ 27,748
Recognized equity compensation cost	9,843
Liability awards	(88)	(1,354)	1,451
Compensation costs	20,775	14,889	27,748
Equity awards
Equity Based Compensation
Compensation costs	11,020	16,243	26,297
Compensation costs	$ 11,020	$ 16,243	$ 26,297

Employee Benefit Plan - Additio

Employee Benefit Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Minimum period following date of hire after which employees become eligible to participate in the Plan	3 months
Employee contribution match in plan (as a percent)	6.00%
Expenses recorded in benefit contributions to the Plan	$ 1	$ 1.5	$ 1.7

Income Taxes - Schedule of Prov

Income Taxes - Schedule of Provision for Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred taxes:
Total	$ 0	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax [Line Items]
Income tax expense or benefit		$ 0	$ 0	$ 0
Federal corporate statutory rate		35.00%	35.00%	35.00%
Unrecognized tax benefits		$ 0	$ 0
Accrued interest or penalties associated with unrecognized tax benefits		$ 0	$ 0
Minimum | Any Person or Entity
Income Tax [Line Items]
Percentage of common stock beneficially owns as result of proposed transfer		4.50%
Federal
Income Tax [Line Items]
Net operating loss carryforwards		$ 2,273,000,000
Net operating loss carryforwards begins to expire		2,026
State
Income Tax [Line Items]
Net operating loss carryforwards		$ 73,300,000
Net operating loss carryforwards begins to expire		2,025
Foreign
Income Tax [Line Items]
Net operating loss carryforwards		$ 51,300,000
Net operating loss carryforwards begins to expire		2,016
Scenario, Forecast
Income Tax [Line Items]
Federal corporate statutory rate	21.00%

Income Taxes - Schedule of Geog

Income Taxes - Schedule of Geographic Sources of Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
U.S.	$ (934,537)	$ (2,313,482)	$ (490,190)
Foreign	(33,721)	(29,827)	(204,236)
Net loss	$ (968,258)	$ (2,343,309)	$ (694,426)

Income Taxes - Schedule of Effe

Income Taxes - Schedule of Effective Tax Rate on Loss (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective tax rate on loss differs form U.S. statutory rates
Income tax expense (benefit) at the federal statutory rate	35.00%	35.00%	35.00%
State income taxes, net of federal income tax benefit	0.10%	0.10%	0.10%
Change in federal statutory rate	(65.40%)
Foreign income tax	3.70%	41.50%	13.50%
Cancellation of debt	(5.70%)	(3.90%)
Other	(0.20%)	(0.10%)	(0.50%)
Valuation allowance	32.50%	(72.60%)	(48.10%)

Income Taxes - Schedule of Tax

Income Taxes - Schedule of Tax Effects of Temporary Differences and Net Operating Losses (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Long-term deferred tax asset:
Seismic and exploration costs	$ 1,753,263	$ 2,227,489
Stock based compensation	11,751	27,342
Domestic NOL carry forwards	481,967	695,434
Foreign NOL carry forwards	26,471	43,969
Other	24,919	11,522
Valuation allowance	(2,289,519)	(2,597,708)
Total long-term deferred tax asset	37,280	408,048
Long-term deferred tax liability:
Oil and natural gas properties	(37,280)	(238,475)
Total long-term deferred tax liability	(37,280)	(408,048)
2019 notes and 2024 notes
Long-term deferred tax asset:
Convertible senior notes, long-term deferred tax asset	$ 28,428
Long-term deferred tax liability:
Convertible senior notes, long-term deferred tax liability		$ (169,573)

Earnings Per Share - Schedule o

Earnings Per Share - Schedule of Earnings Per Share, Basic and Diluted Loss Per Share Computations (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Weighted average common shares outstanding (basic and diluted)	29,556	27,482	27,320
Anti-dilutive shares excluded from diluted loss per share	4,457	6,904	6,980

Earnings Per Share - Schedule76

Earnings Per Share - Schedule of Earnings Per Share, Basic and Diluted Loss Per Share Computations (Parenthetical) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 06, 2016
2.625% convertible senior notes due 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Interest rate (as a percent)	2.625%	2.625%
Debt instrument maturity year	2,019
3.125% convertible senior notes due 2024
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Interest rate (as a percent)	3.125%	3.125%
Debt instrument maturity year	2,024

Other Supplemental Information

Other Supplemental Information - Schedule of Cash, Cash Equivalents and Restricted Cash Recorded in Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents	$ 431,646	$ 613,534
Restricted cash	11,274	2,517
Other assets	15,418
Cash, cash equivalents and restricted cash	$ 458,338	$ 616,051	$ 138,886	$ 258,721

Other Supplemental Informatio78

Other Supplemental Information - Schedule of Supplemental Cash flows and Noncash Transactions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental cash flows information:
Cash paid for interest	$ 142,908	$ 78,320	$ 78,410
Noncash transactions - changes in accrued capital expenditures	$ (57,824)	$ (69,667)	$ (47,580)

Other Supplement Information -

Other Supplement Information - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Accrued Liabilities [Line Items]
Accrued AFE costs	$ 1,203	$ 73,808
Social obligation payments	86,280	86,473
Interest	4,715	13,793
Bonuses	1,522	8,900
General expenses	890	5,849
Seismic and other operating costs	10,996	5,625
Other	3,134	4,799
Total accrued liabilities	136,911	227,418
Angolan
Schedule Of Accrued Liabilities [Line Items]
Angolan consumption tax and withholding on services	9,796	9,796
Block 9
Schedule Of Accrued Liabilities [Line Items]
Funds from release of letter of credit on Block 9	$ 18,375	$ 18,375

Other Matters - Additional Info

Other Matters - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016
Other Commitments [Line Items]
Loss on amendment of contract			$ 95,908
One-time lump sum retention payments amount		$ 19,700
Equity compensation costs		9,843
General and administrative expenses
Other Commitments [Line Items]
One-time lump sum retention expense amount		13,400
Other Assets
Other Commitments [Line Items]
One-time lump sum retention payments amount		11,600
Equity compensation costs		7,000
Unrecognized compensation cost		4,600
Officers
Other Commitments [Line Items]
Repurchase of certain equity awards		12,200
Employees
Other Commitments [Line Items]
Payment of certain retention bonuses		7,500
Contract Termination
Other Commitments [Line Items]
Loss on amendment of contract	$ 95,900
Payment of loss on contract termination		$ 19,600	$ 76,300
Contract termination date		Mar. 31, 2017

Quarterly Data (Unaudited) - Sc

Quarterly Data (Unaudited) - Schedule of Quarterly Data Unaudited (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Selected Quarterly Financial Information [Abstract]
Revenues	$ 15,848	$ 14,427	$ 13,749	$ 9,867	$ 7,768	$ 4,228	$ 3,173	$ 1,636
Gross profit	13,153	11,789	10,714	7,169	5,225	1,855	1,471	680
Net loss	$ (326,817)	$ (149,618)	$ (185,568)	$ (306,255)	$ (1,872,940)	$ (218,207)	$ (205,547)	$ (46,615)
Basic and diluted loss per share	$ (11.03)	$ (5.05)	$ (6.28)	$ (10.40)	$ (67.05)	$ (7.98)	$ (7.52)	$ (1.71)	$ (32.76)	$ (85.27)	$ (25.42)

Quarterly Data (Unaudited) - 82

Quarterly Data (Unaudited) - Schedule of Quarterly Data Unaudited (Parenthetical) (Details) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Exploratory Wells Drilled [Line Items]
Dry hole costs and impairments		$ 237,100	$ 1,761,400	$ 328,910	$ 1,967,180	$ 462,234
Reorganization expenses	$ 332,800			$ 332,772
Shenandoah Discovery
Exploratory Wells Drilled [Line Items]
Dry hole costs and impairments		$ 236,400
Angolan
Exploratory Wells Drilled [Line Items]
Dry hole costs and impairments			$ 1,691,800

Supplementary Information on 83

Supplementary Information on Oil and Natural Gas Activities (Unaudited) - Schedule of Capitalized Costs Relating to Oil and Natural Gas Producing Activities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Extractive Industries [Abstract]
Proved oil and natural gas properties	$ 127,005	$ 118,245
Unproved oil and natural gas properties, net	850,452	980,844
Gross capitalized costs	977,457	1,099,089
Accumulated depreciation, depletion and amortization	(60,516)	(20,204)
Net capitalized costs	$ 916,941	$ 1,078,885

Supplementary Information on 84

Supplementary Information on Oil and Natural Gas Activities (Unaudited) - Schedule of Costs Incurred in Oil and Natural Gas Property Development Activities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Extractive Industries [Abstract]
Acquisition of unproved oil and natural gas properties	$ 1,369	$ 3,715	$ 35,993
Exploration costs:
Capitalized	197,096	599,526	718,078
Expensed	47,477	58,170	61,844
Development costs	8,761	39,111	145,021
Total	$ 254,703	$ 700,522	$ 960,936

Supplementary Information on 85

Supplementary Information on Oil and Natural Gas Activities (Unaudited) - Schedule of Changes in Estimated Proved and Estimated Proved Developed Reserves (Details)	12 Months Ended
	Dec. 31, 2017MMBoeMMBblsBcf	Dec. 31, 2016MMBoeMMBblsBcf	Dec. 31, 2015MMBoeMMBblsBcf	Dec. 31, 2014MMBoeMMBblsBcf
Proved developed and undeveloped energy reserves:
Beginning of the year | MMBoe	3.3	6.2	9
Revisions of previous estimates | MMBoe	(0.9)	(2.5)	(2.8)
Production | MMBoe	(1.1)	(0.4)
End of the year | MMBoe	1.3	3.3	6.2
Proved developed energy reserves:
Proved developed energy reserves | MMBoe	1.3	2.1
Proved undeveloped energy reserves:
Proved undeveloped energy reserves | MMBoe		1.2	6.2	9
Oil (MMBbls)
Proved developed and undeveloped reserves:
Beginning of the year	3	5.6	8.4
Revisions of previous estimates	(0.9)	(2.2)	(2.8)
Production	(1)	(0.4)
End of the year	1.1	3	5.6
Proved developed reserves:
Proved developed reserves	1.1	1.9
Proved undeveloped reserves:
Proved undeveloped reserves		1.1	5.6	8.4
Natural Gas (Bcf)
Proved developed and undeveloped reserves:
Beginning of the year | Bcf	1.2	1.8	3.7
Revisions of previous estimates | Bcf	(0.5)	(0.5)	(1.9)
Production | Bcf	(0.3)	(0.1)
End of the year | Bcf	0.4	1.2	1.8
Proved developed reserves:
Proved developed reserves | Bcf	0.4	0.8
Proved undeveloped reserves:
Proved undeveloped reserves | Bcf		0.4	1.8	3.7
Natural Gas Liquids (MMBbls)
Proved developed and undeveloped reserves:
Beginning of the year	0.1	0.3
Revisions of previous estimates		(0.2)	0.3
Production	(0.1)
End of the year		0.1	0.3
Proved developed reserves:
Proved developed reserves		0.1
Proved undeveloped reserves:
Proved undeveloped reserves			0.3

Supplementary Information on 86

Supplementary Information on Oil and Natural Gas Activities (Unaudited) - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017$ / bbl$ / Mcf	Dec. 31, 2016$ / bbl$ / Mcf	Dec. 31, 2015$ / bbl$ / Mcf
Supplemental Information On Oil And Gas Exploration And Production Activities Disclosure [Line Items]
Future net cash flows discounted at an annual rate	10.00%
Oil (MMBbls)
Supplemental Information On Oil And Gas Exploration And Production Activities Disclosure [Line Items]
Average resulting price (in dollars per Bbl, NGL or Mcf)	51.04	40.32	50.78
Natural Gas Liquids
Supplemental Information On Oil And Gas Exploration And Production Activities Disclosure [Line Items]
Average resulting price (in dollars per Bbl, NGL or Mcf)	31.68	19.23	15.23
Natural Gas
Supplemental Information On Oil And Gas Exploration And Production Activities Disclosure [Line Items]
Average resulting price (in dollars per Bbl, NGL or Mcf) | $ / Mcf	2.284	2.056	(0.182)

Supplementary Information on 87

Supplementary Information on Oil and Natural Gas Activities (Unaudited) - Schedule of Standardized Measure of Discounted Future Net Cash Flows Relating to Estimated Proved Oil, Natural Gas and Natural Gas Liquids Reserves (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Future net cash flows relating to estimated proved oil, natural gas and natural gas liquids reserves based on the standardized measure
Future cash inflows	$ 60,665	$ 123,889	$ 288,705
Future production and development costs	(48,591)	(86,103)	(186,053)
Future net cash flows	12,074	37,786	102,652
10% annual premium (discount) for estimated timing of cash flows	5,231	1,164	(45,077)
Standardized measure of discounted future net cash flows	$ 17,305	$ 38,950	$ 57,575	$ 365,284

Supplementary Information on 88

Supplementary Information on Oil and Natural Gas Activities (Unaudited) - Schedule of Changes in Standardized Measure of Future Net Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Extractive Industries [Abstract]
Standardized measure at beginning of year	$ 38,950	$ 57,575	$ 365,284
Sales and transfers of oil, natural gas and natural gas liquids produced, net of production costs	(42,825)	(9,231)
Net changes in prices and production costs	17,084	(31,738)	(314,367)
Development costs incurred during the period	7,589	45,611
Revisions and other	(15,218)	(23,579)	(122,584)
Accretion of discount	3,895	5,757	36,528
Changes in estimated future development costs	7,589	(822)	99,964
Changes in timing and other	241	(4,623)	(7,250)
Standardized measure, ending	$ 17,305	$ 38,950	$ 57,575