Century Aluminum (CENX) 10-K 2 Mar 15 2014 FY Annual report Financial data

Document_And_Entity_Informatio

Document And Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Jan. 31, 2015	Jun. 30, 2014
Document Information [Line Items]
Entity Registrant Name	CENTURY ALUMINUM CO
Entity Central Index Key	949157
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$808,000,000
Entity Common Stock, Shares Outstanding		89,064,582
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14

CONSOLIDATED_STATEMENTS_OF_OPE

CONSOLIDATED STATEMENTS OF OPERATIONS (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
NET SALES:
Third-party customers	$668,941	$943,262	$719,812
Related parties	1,262,101	511,051	552,299
Sales Revenue – net	1,931,042	1,454,313	1,272,111
Cost of goods sold	1,728,586	1,414,790	1,225,769
Gross profit	202,456	39,523	46,342
Other operating expense – net	12,481	8,602	18,253
Selling, general and administrative expenses	49,195	67,477	35,363
Operating income (loss)	140,780	-36,556	-7,274
Interest expense	-22,015	-23,091	-24,029
Interest income	301	728	554
Net gain (loss) on forward and derivative contracts	179	16,598	-4,150
Gain on bargain purchase	0	5,253	0
Gain on fair value of contingent consideration	7,943	0	0
Gain on remeasurement of equity investment	1,318	0	0
Loss on early extinguishment of debt	0	-3,272	0
Other income – net	991	496	5,576
Income (loss) before income taxes and equity in earnings of joint ventures	129,497	-39,844	-29,323
Income tax expense	-18,308	-3,131	-8,910
Income (loss) before equity in earnings of joint ventures	111,189	-42,975	-38,233
Equity in earnings of joint ventures	1,305	2,662	2,623
Net income (loss)	$112,494	($40,313)	($35,610)
EARNINGS (LOSS) PER COMMON SHARE:
Earnings Per Share, Basic (in dollars per share)	$1.16	($0.45)	($0.40)
Earnings Per Share, Diluted (in dollars per share)	$1.15	($0.45)	($0.40)

CONSOLIDATED_STATEMENTS_OF_COM

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Comprehensive income (loss):
Net income (loss)	$112,494	($40,313)	($35,610)
Other comprehensive income (loss) before income tax effect:
Net unrealized loss on financial instruments	0	0	-218
Net loss reclassified to income on financial instruments	0	0	567
Net gain on foreign currency cash flow hedges reclassified as income	-186	-186	-186
Net gain (loss) arising during the period	-41,995	56,795	-16,691
Prior service cost arising during the period	-1,299	0	0
Amortization of prior service benefit during the period	-3,504	-3,920	-4,113
Amortization of net loss during the period	10,312	8,174	9,837
Change in equity in investee other comprehensive income	0	61	-4,236
Other comprehensive income (loss) before income tax effect	-36,672	60,924	-15,040
Income tax effect	-1,829	-1,564	-1,564
Other comprehensive income (loss)	-38,501	59,360	-16,604
Total comprehensive income (loss)	$73,993	$19,047	($52,214)

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Thousands, unless otherwise specified
ASSETS
Cash and cash equivalents	$163,242		$84,088
Restricted cash	801		1,697
Accounts receivable — net	76,165		56,184
Due from affiliates	31,503		43,587
Inventories	283,480	[1]	239,615	[1]
Prepaid and other current assets	29,768		32,276
Deferred taxes	14,281		13,614
Total current assets	599,240		471,061
Property, plant and equipment — net	1,291,218		1,247,661
Other assets	123,577		91,474
TOTAL	2,014,035	[2]	1,810,196	[2]
LIABILITIES:
Accounts payable, trade	151,443		108,490
Due to affiliates	22,261		53,582
Accrued and other current liabilities	104,646		69,466
Accrued employee benefits costs	10,159		8,410
Industrial revenue bonds	7,815		7,815
Total current liabilities	296,324		247,763
Senior notes payable	246,888		246,528
Accrued pension benefits costs — less current portion	59,906		39,848
Accrued postretirement benefits costs — less current portion	152,894		129,284
Other liabilities	53,272		37,743
Deferred taxes	113,604		106,218
Total noncurrent liabilities	626,564		559,621
COMMITMENTS AND CONTINGENCIES (NOTE 15)
SHAREHOLDERS’ EQUITY:
Series A Preferred stock (one cent par value, 5,000,000 shares authorized; 160,000 issued and 78,141 outstanding at December 31, 2014; 160,000 issued and 79,620 outstanding at December 31, 2013)	1		1
Common stock (one cent par value, 195,000,000 shares authorized; 93,851,103 issued and 89,064,582 outstanding at December 31, 2014; 93,496,798 issued and 88,710,277 outstanding at December 31, 2013)	939		935
Additional paid-in capital	2,510,261		2,508,574
Treasury stock, at cost	-49,924		-49,924
Accumulated other comprehensive loss	-117,682		-91,832
Accumulated deficit	-1,252,448		-1,364,942
Total shareholders’ equity	1,091,147		1,002,812
TOTAL	$2,014,035		$1,810,196
[1]	Includes inventory acquired in connection with the Mt. Holly acquisition. See Note 2 Business acquisitions for additional information about the Mt. Holly acquisition.
[2]	Segment assets include accounts receivable, due from affiliates, prepaid and other current assets, inventory, intangible assets and property, plant and equipment — net; the remaining assets are unallocated corporate assets.

CONSOLIDATED_BALANCE_SHEETS_Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Series A Preferred stock, par value (in dollars per share)	$0.01	$0.01
Series A Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Series A Preferred stock, shares issued (in shares)	160,000	160,000
Series A Preferred stock, shares outstanding (in shares)	78,141	79,620
Common stock, par value (in dollars per share)	$0.01	$0.01
Common stock, shares authorized (in shares)	195,000,000	195,000,000
Common stock, shares issued (in shares)	93,851,103	93,496,798
Common stock, shares outstanding (in shares)	89,064,582	88,710,277

CONSOLIDATED_STATEMENTS_OF_SHA

CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (USD $)	Total	Preferred stock [Member]	Common stock [Member]	Additional paid-in capital [Member]	Treasury stock, at cost [Member]	Accumulated other comprehensive loss [Member]	Accumulated deficit [Member]
In Thousands
Balance at Dec. 31, 2011	$1,038,277	$1	$932	$2,506,842	($45,891)	($134,588)	($1,289,019)
Net income (loss)	-35,610	0	0	0	0	0	-35,610
Other comprehensive income (loss)	-16,604	0	0	0	0	-16,604	0
Issuance of common stock – compensation plans	0	0	1	-1	0	0	0
Repurchase of common stock	-4,033	0	0	0	-4,033	0	0
Share-based compensation expense	613	0	0	613	0	0	0
Balance at Dec. 31, 2012	982,643	1	933	2,507,454	-49,924	-151,192	-1,324,629
Net income (loss)	-40,313	0	0	0	0	0	-40,313
Other comprehensive income (loss)	59,360	0	0	0	0	59,360	0
Issuance of common stock – compensation plans	44	0	1	43	0	0	0
Share-based compensation expense	1,078	0	0	1,078	0	0	0
Conversion of preferred stock to common stock	0	0	1	-1	0	0	0
Balance at Dec. 31, 2013	1,002,812	1	935	2,508,574	-49,924	-91,832	-1,364,942
Net income (loss)	112,494	0	0	0	0	0	112,494
Other comprehensive income (loss)	-38,501	0	0	0	0	-38,501	0
Elimination of equity in investee resulting from acquisition	12,651	0	0	0	0	12,651	0
Issuance of common stock – compensation plans	304	0	2	302	0	0	0
Share-based compensation expense	1,387	0	0	1,387	0	0	0
Conversion of preferred stock to common stock	0	0	2	-2	0	0	0
Balance at Dec. 31, 2014	$1,091,147	$1	$939	$2,510,261	($49,924)	($117,682)	($1,252,448)

CONSOLIDATED_STATEMENTS_OF_CAS

CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$112,494	($40,313)	($35,610)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Unrealized net loss (gain) on forward contracts	0	-1,170	2,987
Gain on bargain purchase	0	-5,253	0
Gain on fair value of contingent consideration	-7,943	0	0
Gain on remeasurement of equity investment	-1,318	0	0
Unrealized gain on E.ON contingent obligation	-1,412	-16,781	0
Accrued and other plant curtailment costs — net	4,350	4,452	5,251
Lower of cost or market inventory adjustment	-1,247	1,247	-19,818
Depreciation	70,731	66,570	62,570
Sebree power contract amortization	-5,534	-31,031	0
Debt discount amortization	361	672	1,069
Pension and other postretirement benefits	6,939	1,740	3,129
Deferred income taxes	2,633	-1,493	1,529
Stock-based compensation	1,334	1,078	613
Loss on early extinguishment of debt	0	3,272	0
Equity in earnings of joint ventures, net of dividends	425	871	-2,623
Change in operating assets and liabilities:
Accounts receivable — net	-19,981	-6,001	-2,537
Due from affiliates	12,084	-5,717	2,202
Inventories	-16,513	-21,740	31,854
Prepaid and other current assets	3,392	5,318	4,946
Accounts payable, trade	11,797	25,224	-12,114
Due to affiliates	3,058	13,845	-2,167
Accrued and other current liabilities	18,071	5,834	-5,746
Other — net	2,690	19,094	1,604
Net cash provided by operating activities	196,411	19,718	37,139
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property, plant and equipment	-41,559	-46,533	-17,677
Nordural expansion — Helguvik	-337	-3,331	-7,317
Purchase of carbon anode assets and improvements	-13,230	-18,213	-13,814
Purchase of Sebree smelter	-1,042	-48,058	0
Investments in and advances to joint ventures	0	-125	-275
Payments received from joint ventures	0	0	6,622
Purchase of remaining interest in Mt. Holly smelter	-53,831	0	0
Proceeds from sale of property, plant and equipment	46	525	188
Restricted and other cash deposits	896	-1,439	-258
Net cash used in investing activities	-109,057	-117,174	-32,531
CASH FLOWS FROM FINANCING ACTIVITIES:
Repayment of debt	-2,603	-249,604	0
Proceeds from issuance of debt	0	246,330	0
Borrowings under revolving credit facilities	92,423	22,725	18,076
Repayments under revolving credit facilities	-98,423	-16,725	-18,076
Debt issuance costs	0	-3,994	0
Debt retirement costs	0	-1,208	0
Repurchase of common stock	0	0	-4,033
Issuance of common stock	403	44	0
Net cash used in financing activities	-8,200	-2,432	-4,033
CHANGE IN CASH AND CASH EQUIVALENTS	79,154	-99,888	575
Cash and cash equivalents, beginning of year	84,088	183,976	183,401
Cash and cash equivalents, end of year	$163,242	$84,088	$183,976

Summary_of_significant_account

Summary of significant accounting policies	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Summary of significant accounting policies	Summary of significant accounting policies
	Organization and Basis of Presentation — Century Aluminum Company ("Century Aluminum," "Century," the "Company", "we", "us", "our" or "ours") is a holding company, whose principal subsidiaries are Century Kentucky, Inc. (together with its subsidiaries, "CAKY"), Nordural ehf ("Nordural"), Century Aluminum Sebree LLC ("Century Sebree"), Century Aluminum of South Carolina ("CASC"), and Century Aluminum of West Virginia, Inc. ("Century of West Virginia").  Century Kentucky, Inc. operates a primary aluminum reduction facility in Hawesville, Kentucky ("Hawesville").  Nordural Grundartangi ehf, a subsidiary of Nordural, operates a primary aluminum reduction facility in Grundartangi, Iceland ("Grundartangi").  Century Sebree operates a primary aluminum reduction facility in Robards, Kentucky ("Sebree"). Century of West Virginia owns a primary aluminum reduction facility in Ravenswood, West Virginia ("Ravenswood").  CASC operates a primary aluminum reduction facility in Mt. Holly, South Carolina ("Mt. Holly"). We are constructing a primary aluminum facility in Helguvik, Iceland ("Helguvik" or the "Helguvik project") which is owned and would be operated through Nordural Helguvik ehf, a subsidiary of Nordural.
	Mt. Holly was operated as a joint venture between us and Alumax of South Carolina Inc. ("Alumax of SC") until our wholly-owned subsidiary, Berkeley Aluminum, Inc. ("Berkeley"), acquired Alumax of SC in December 2014. See Note 2 Business acquisitions for additional information about the Acquisition. Prior to the acquisition, Berkeley held a 49.7% interest in the partnership which operated Mt. Holly and a 49.7% undivided interest in the property, plant, and equipment comprising Mt. Holly.  The remaining interest in the partnership and the remaining undivided interest in Mt. Holly's property, plant and equipment were owned by Alumax of SC.  Alcoa managed and operated Mt. Holly pursuant to an Owners Agreement. Pursuant to the Owners Agreement, each owner furnished their own alumina, for conversion to aluminum, and was responsible for their pro rata share of the operating and conversion costs.
	In 2013, Century Sebree, acquired Sebree from a subsidiary of Rio Tinto Alcan, Inc. ("RTA").
	In 2012, our wholly owned subsidiary, Century Aluminum Vlissingen B.V. ("Century Vlissingen") purchased a carbon anode production facility located in Vlissingen, the Netherlands ("Vlissingen"). Vlissingen restarted operations in late 2013 and supplies carbon anodes to Grundartangi.
	We also own a 40% stake in Baise Haohai Carbon Co., Ltd. ("BHH"), a joint venture that owns and operates a carbon anode and cathode facility located in the Guangxi Zhuang Autonomous Region of south China.  BHH supplies anodes to Grundartangi.
	Prior to our initial public offering, we were an indirect, wholly-owned subsidiary of Glencore plc (together with its subsidiaries, "Glencore").  At December 31, 2014, based on their filings with the Securities and Exchange Commission, Glencore owned 41.8% of Century’s outstanding common stock and all of our outstanding Series A Convertible Preferred stock. Through its ownership of our common and preferred stock, Glencore has an overall 46.5% economic ownership of Century.  Century and Glencore enter into various transactions such as the purchase and sale of primary aluminum, purchase and sale of alumina, tolling agreements and certain forward financial contracts.
	Principles of Consolidation — The consolidated financial statements include the accounts of Century Aluminum Company and our subsidiaries, after elimination of all intercompany transactions and accounts. Our interest in the BHH joint venture are accounted for under the equity method. For BHH, we report our investment in its results of operations on a one-quarter lag.
	Reclassification — Certain immaterial amounts reported in previous years have been reclassified to conform to the current period presentation.
	Revenue recognition — Revenue is recognized when title and risk of loss pass to customers in accordance with contract terms.  In some instances, we invoice our customers prior to physical shipment of goods.  In such instances, revenue is recognized only when the customer has specifically requested such treatment and has made a commitment to purchase the product.  The goods must be complete, ready for shipment and physically separated from other inventory with risk of ownership passing to the customer.  We must retain no performance obligations.
	Cash and Cash Equivalents — Cash and cash equivalents are comprised of cash, money market funds and short-term investments having original maturities of three months or less. The carrying amount of cash equivalents approximates fair value.
	Accounts Receivable — The accounts receivable are net of an allowance for uncollectible accounts of $1,000 and $734 at December 31, 2014 and 2013, respectively.
	Inventories — Our inventories are stated at the lower of cost or market ("LCM"), using the first-in, first-out ("FIFO") method.
	Property, Plant and Equipment — Property, plant and equipment is stated at cost.  Additions, renewals and improvements are capitalized.  Asset and accumulated depreciation accounts are relieved for dispositions with resulting gains or losses included in other income – net.  Maintenance and repairs are expensed as incurred.  We capitalize interest for the construction of qualifying assets.  Depreciation of plant and equipment is provided for by the straight-line method over the following estimated useful lives:
	Building and improvements    10 to 45 years
	Machinery and equipment         5 to 35 years
	Impairment of long-lived assets — We review our property, plant and equipment for potential impairment whenever events or circumstances indicate that the carrying amount of these assets (asset group) may not be recoverable.  The carrying amount of the assets (asset group) is not recoverable if it exceeds the sum of the undiscounted cash flows expected to result from the use and eventual disposition of the assets (asset group). In that case, an impairment loss would be recognized for the amount in which the carrying amount exceeds the fair value of the assets (asset group), with the fair value determined using the anticipated cash flows discounted at a rate commensurate with the risk involved. We estimate the future cash flows using management’s assumptions about the expected future use of the assets (asset group), the remaining useful life, expenditures to maintain the service potential, market and other cost assumptions.
	Determination as to whether and how much an asset is impaired involves significant management judgment involving highly uncertain matters, including estimating the future sales volumes, future selling prices and cost, alternative uses for the asset, and estimated proceeds from the disposal of the asset.  However, the impairment reviews and calculations are based on estimates and assumptions that take into account our business plans and long-term investment decisions at the time of such impairment reviews. We did not recognize any impairment losses on our long-lived fixed assets during 2014, 2013 or 2012.
	Business Acquisitions — We account for business acquisitions by applying the acquisition method in accordance with Financial Accounting Standards Board ("FASB") Accounting Standards Codification ("ASC") 805 "Business Combinations." We allocate the purchase price to the assets acquired and liabilities assumed based on their estimated fair values on the date of the acquisition. The difference between the fair value of the net assets acquired and the purchase price is recorded as either goodwill or a bargain purchase gain. We record the operating results of our acquired businesses in our consolidated statements of operations from the date of acquisition.
	Other Assets — Other assets consist primarily of Century’s investments in joint ventures, deferred financing costs, assets held in a Rabbi trust to fund the non-qualified supplemental executive retirement benefits ("SERB") pension benefit obligation, prepaid power costs, internal use software and operating maintenance supplies not expected to be consumed within the year. Our equity share of the undistributed earnings (loss) increases (decreases) the investment in the joint ventures.  Deferred financing costs are amortized on a straight-line basis over the life of the related financial instrument.
	Prior to the Acquisition, we accounted for our interest in the Mt. Holly partnership using the equity method of accounting.  Additionally, our undivided interest in certain property, plant and equipment of Mt. Holly was held outside of the partnership and the undivided interest in these assets of the facility was accounted for in accordance with the ASC 810-10-45-14 "Investor Balance Sheet and Income Statement Display under the Equity Method for Investments in Certain Partnerships and Other Ventures."  Accordingly, prior to the Acquisition, the undivided interest in these assets and the related depreciation were accounted for on a proportionate gross basis.
	Income Taxes — We account for income taxes using the asset and liability method, whereby deferred income taxes reflect the net tax effect of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes.  In evaluating our ability to realize deferred tax assets, we use judgment in considering the relative impact of negative and positive evidence. The weight given to the potential effect of negative and positive evidence is commensurate with the extent to which it can be objectively verified.  Based on the weight of evidence, both negative and positive, if it is more likely than not that some portion or all of a deferred tax asset will not be realized, a valuation allowance is established.  Accordingly, we have a valuation allowance against all of our net federal and state deferred tax assets.  We have a valuation allowance against a portion of our Icelandic and all of our Hong Kong and the Netherlands net operating loss ("NOL") deferred tax assets due to our belief that it is more likely than not that these assets will not be realized.  During 2012, we removed our election to permanently reinvest foreign earnings. See Note 14 Income taxes for additional information.
	Defined Benefit Pension and Other Postretirement Benefits — We sponsor defined benefit pension and other postretirement benefit ("OPEB") plans for certain of our domestic hourly and salaried employees. We recognize expenses, assets and liabilities based on actuarial assumptions. We contribute to our defined benefit pension plans based upon actuarial and economic assumptions designed to achieve adequate funding of the projected benefit obligations and to meet the minimum funding requirements.  In addition, we maintain the SERB plan for certain current and former executive officers.  We account for these plans in accordance with ASC 715 "Compensation — Retirement Benefits." We use a measurement date of December 31st to determine the pension and OPEB liabilities.
	Postemployment Benefits — We provide certain postemployment benefits to certain former and inactive employees and their dependents during the period following employment, but before retirement. These benefits include salary continuance, supplemental unemployment and disability healthcare.  We recognize the estimated future cost of providing postemployment benefits on an accrual basis over the active service life of the employee.
	Derivatives and hedging — We enter into fixed and market priced contracts for the sale of primary aluminum and the purchase of raw materials in future periods.  We also enter into fixed price financial sales contracts and put option contracts to manage our exposure to changing primary aluminum prices.
	Certain physical delivery and financial sales contracts for primary aluminum that are not designated cash flow hedges or do not qualify for cash flow hedge treatment are marked-to-market quarterly.  Fluctuations in the London Metal Exchange ("LME") price of primary aluminum may have a significant impact on gains and losses included in our financial statements from period to period.  We recognize the unrealized and realized gains and losses associated with these contracts in net gain (loss) on forward and derivative contracts.
	See Note 4 Fair value measurements and Note 5 Derivatives and hedging instruments for additional information about these contracts.
	Foreign Currency – We are exposed to foreign currency risk due to fluctuations in the value of the U.S. dollar as compared to the euro, the Icelandic krona ("ISK") and the Chinese yuan.  Grundartangi and Vlissingen use the U.S. dollar as their functional currency, however a portion of the operating expenses of their respective facilities are denominated and payable in currencies other than the U.S. dollar.  Grundartangi’s labor costs, part of its maintenance costs and other local services are denominated in ISK and a portion of its anode costs are denominated in euros.  Labor costs, maintenance costs and other local services at Vlissingen are denominated in euros. Transactions denominated in currencies other than the functional currency are recorded based on exchange rates at the time such transactions arise and any transaction gains and losses are reflected in other income – net in the consolidated statements of operations. As a result, an increase or decrease in the value of those currencies relative to the U.S. dollar would affect Grundartangi’s and Vlissingen's operating margins.  In addition, our joint venture investment in BHH uses the Chinese yuan as its functional currency.  For our joint venture investments, we record gains and losses associated with foreign currency exchange rates in equity in earnings of joint ventures.
	Financial Instruments — Our receivables, certain life insurance policies, payables, borrowings under our revolving credit facilities and debt related to industrial revenue bonds ("IRBs") are carried at amounts that approximate fair value.  The following table provides the carrying amounts and approximate fair values (based on the last available trading data) of our 7.5% senior secured notes due 2021 (the "7.5% Notes due 2021") and our 7.5% senior unsecured notes due 2014 (the "7.5% Notes due 2014"). See Note 4 Fair value measurements for additional information about these financial instruments.
		December 31, 2014				December 31, 2013
		Carrying amount		Fair value		Carrying amount		Fair value
	7.5% Notes due 2021	$	246,888	$	256,408	$	246,528	$	244,375
	7.5% Notes due 2014	—		—		2,603		2,487
	Earnings per share — Basic earnings (loss) per share ("EPS") amounts are calculated by dividing earnings (loss) available to common stockholders by the weighted average number of common shares outstanding.  Diluted EPS amounts assume the issuance of common stock for all potentially dilutive common shares outstanding.
	Our Series A Convertible Preferred Stock has similar characteristics to a "participating security" as described by ASC 260 "Earnings per Share" and we calculate the amount of net income (loss) allocated to common stockholders and basic EPS using the Two-Class Method earnings allocation formula, allocating undistributed income to our preferred shareholder consistent with their participation rights, and diluted EPS using the If-Converted Method when applicable.
	Our Series A Convertible Preferred Stock is a non-cumulative perpetual participating convertible preferred stock with no set dividend preferences.  The holders of our convertible preferred stock do not have a contractual obligation to share in our losses.  In periods where we report net losses, we do not allocate these losses to the convertible preferred stock for the computation of basic or diluted EPS.
	Asset Retirement Obligations — We are subject to environmental regulations which create certain legal obligations related to the normal operations of our domestic primary aluminum smelter operations. Our asset retirement obligations ("AROs") consist primarily of costs associated with the disposal of spent pot liner used in the reduction cells of our domestic facilities. AROs are recorded on a discounted basis, at the time the obligation is incurred (when the pot liner is put in service) and accreted over time for the change in the present value of the liability. We capitalize the asset retirement costs by increasing the carrying amount of the related long-lived assets and depreciating these assets over their remaining useful lives.
	Certain conditional asset retirement obligations ("CAROs") related to the disposal costs of fixed assets at our primary aluminum facilities have not been recorded because they have an indeterminate settlement date.  CAROs are a legal obligation to perform an asset retirement activity in which the timing and (or) method of settlement are conditional on a future event that may or may not be within our control. We would recognize a CARO in the period in which sufficient information exists to reasonably estimate the fair value of the liability. These CAROs relate to the remediation of our primary aluminum facilities for certain regulated assets and hazardous material, such as landfills and asbestos and various other materials.
	Concentrations of Credit Risk — Financial instruments, which potentially expose us to concentrations of credit risk, consist principally of trade receivables.  Our limited customer base increases our concentrations of credit risk with respect to trade receivables. We routinely assess the financial strength of our customers and collectability of our trade receivables.
	Use of Estimates — The preparation of financial statements in conformity with generally accepted accounting principles in the United States ("GAAP") requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
	Share-Based Compensation — We measure the cost of employee services received in exchange for an award of equity instruments based on the grant-date fair value of the award. We recognize the cost over the period during which an employee is required to provide service in exchange for the award—the requisite service period (usually the vesting period). No compensation cost is recognized for equity instruments for which employees do not render the requisite service.
	The grant-date fair value of service-based share awards is equal to the closing stock price on the date of the grant. Stock option grant-date fair value is estimated using the Black-Scholes option-pricing model adjusted for the unique characteristics of those instruments. We have not issued any stock options since 2009. If an equity award is modified after the grant date, incremental compensation cost will be recognized in an amount equal to the excess of the fair value of the modified award over the fair value of the original award immediately before the modification.
	We issue shares to satisfy the requirements of our share-based compensation plans. At this time, we do not plan to issue treasury shares to support our share-based compensation plans, but we may in the future.
	We award performance units to certain officers and employees. The performance units may be settled in cash or common stock at the discretion of the Board. These awards have historically been settled in cash, and we expect that to continue.
	Recently Issued Accounting Standards – We evaluate the impact of FASB Accounting Standards Updates ("ASUs") issued.  When the adoption or planned adoption of recently issued ASUs will potentially have a material impact on our consolidated financial position, results of operations and cash flows, we disclose the quantitative and qualitative effects of the adoption in our consolidated financial statements.
	In May 2014, the FASB and International Accounting Standards Board ("IASB") issued their final standard on revenue from contracts with customers. The standard, issued as ASU 2014-09 "Revenue From Contracts with Customers" by the FASB, outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance.
	Compared with current GAAP, the ASU requires significantly expanded disclosures about revenue recognition. The ASU is effective for Century for our fiscal year 2017 and thereafter. Early adoption is not permitted. We are currently evaluating the impact of adoption on our consolidated financial position, results of operations and cash flows.

Business_acquisitions_Notes

Business acquisitions (Notes)	12 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Business acquisitions	Business acquisitions
	Acquisition of Mt. Holly aluminum smelter
	On October 23, 2014, Berkeley entered into a stock purchase agreement (the "Stock Purchase Agreement") with Alumax Inc. ("Alumax"), a wholly owned subsidiary of Alcoa, to acquire Alcoa’s 50.3% stake in Mt. Holly. Upon closing of the transaction on December 1, 2014, Century owns 100% of Mt. Holly. Mt. Holly, located in Goose Creek, South Carolina, employs approximately 600 people and has an annual production capacity of 231,000 tonnes of primary aluminum.
	Pursuant to the terms of the Stock Purchase Agreement, Berkeley agreed to acquire all of the issued and outstanding shares of capital stock of Alumax of SC for $67,500 in cash less certain amounts owed by Alumax to Mt. Holly and subject to working capital and other similar adjustments, of which we have paid approximately $53,831 as of December 31, 2014. The acquisition was funded with available cash on hand. We incurred $1,087 of acquisition-related costs during 2014. All acquisition-related costs were expensed to selling, general and administrative expenses during 2014.
	Pension funding obligations
	Alcoa spun-off the pension plan assets for the Mt. Holly employees and former employees into a qualified defined benefit pension plan established by Century. The new Mt. Holly pension plan benefit obligations were measured based on termination basis under IRS Code Section 414(l). The Mt. Holly pension plan was fully funded using the Pension Benefit Guaranty Corporation ("PBGC") assumptions, which are more conservative than the assumptions we use to measure our defined benefit obligations, and resulted in the recognition of a pension asset at closing.
	Contingent Consideration - Earn-out provision
	The Stock Purchase Agreement provides for a post-closing cash payment to be made following December 31, 2015 based on (i) changes in the Midwest Transaction Price for aluminum between July 2, 2014 and December 31, 2015 and (ii) the aggregate cast house production of Mt. Holly from October 1, 2014 through December 31, 2015. The maximum amount of this post-closing cash payment by (i) CASC to Alumax is $22,500 and (ii) Alumax to CASC is $12,500. We measured the fair value of the contingent consideration and recognized a $13,780 liability at December 1, 2014. Each period, until the end of the measurement period on December 31, 2015, we will remeasure the fair value of the contingent consideration. Any changes in the fair value will be recognized in earnings. In December 2014, we recognized $7,943 in gain on fair value of contingent consideration, primarily related to decreases in the forward curve of the LME price of primary aluminum.
	Step Acquisition
	In accordance with ASC 805, we accounted for this transaction as a step acquisition which required that we remeasure our existing 49.7% ownership interest (previously accounted for as an equity method investment) to fair value. The fair value of our interest in Mt. Holly was $56,723 at closing, resulting in a non-cash pre-tax gain of $1,318 included in gain on remeasurement of equity investment on our consolidated statements of operations for 2014. Our previously recorded equity method investment in Mt. Holly and the proportionally consolidated property, plant and equipment was derecognized from our consolidated balance sheets. Since the date of the step acquisition, the financial results of Mt. Holly were included within our consolidated financial statements.
	The allocation of the purchase price to the assets acquired and liabilities assumed is based on the estimated fair values at the date of acquisition. The purchase price allocation is preliminary and subject to change based on the finalization of the valuation of assets and liabilities and the fair value of the previously held equity investment. The amounts presented below represent our estimates based on a preliminary valuation of certain assets and liabilities in connection with the acquisition of the Mt. Holly smelter. The results of the valuation are currently under review by management and are expected to be finalized in the second quarter of 2015.
	The following table summarizes the preliminary fair value of the assets acquired and the liabilities assumed as of the acquisition date:
		Acquisition Date Fair Value as of December 1, 2014
	Consideration:
	Purchase price	$	67,500
	Pension funding (1)	46,546
	Contingent consideration	13,780
	Economic, working capital and other closing adjustments (1)	(12,324		)
	Settlement of partnership accounts	(23,172		)
	Fair value of existing equity investment	56,723
	Total consideration	$	149,053
	Assets Acquired:
	Inventories	$	26,105
	Due from Alumax	20,786
	Prepaid and other current assets	2,527
	Intangible asset	2,580
	Pension asset (1)	30,842
	Property, plant and equipment – net	127,089
	Total assets acquired	$	209,929
	Liabilities Assumed:
	Accounts payable, trade	$	41,471
	Accrued and other current liabilities	8,335
	Accrued postretirement benefit costs (1)	2,857
	Other liabilities	8,213
	Deferred taxes	4,804
	Total liabilities assumed	$	65,680
	Goodwill	$	4,804
	-1	These amounts represents our preliminary estimates based on our current expectation of the pension, working capital, economic and other closing adjustments. These estimates are subject to review and approval by both parties. The final determination and payment of the settlement amounts is expected in the second quarter of 2015.
	From the acquisition date of December 1, 2014 through December 31, 2014, the revenue and earnings that were attributable to the acquired Alcoa’s 50.3% stake in Mt. Holly included in the consolidated statement of operations is as follows:
		Year ended December 31,
		2014
	Mt. Holly revenue	$	25,911
	Mt. Holly income from continuing operations (1)	3,024
	-1	The income attributable to the acquired Alcoa’s 50.3% stake in Mt. Holly excludes the gain on the fair value of the contingent consideration and the gain on remeasurement of the equity investment.
	The following unaudited pro forma financial information for the years ended December 31, 2014 and December 31, 2013 reflects our results of continuing operations as if the acquisition of the remaining interest in Mt. Holly had been completed on January 1, 2013. This unaudited pro forma financial information is provided for informational purposes only and is not necessarily indicative of what the actual results of operations would have been had the transactions taken place on January 1, 2013, nor is it indicative of the future consolidated results of operations or financial position of the combined companies.
		Year ended December 31,
		2014			2013
	Pro forma revenues	$	2,176,552		$	1,707,838
	Pro forma earnings (loss) from continuing operations	125,847			(38,819		)
	Pro forma earnings (loss) per common share, basic	1.3			(0.44		)
	Pro forma earnings (loss) per common share, diluted	1.29			(0.44		)
	Transactions Recognized Separately from the Mt. Holly acquisition
	As part of the acquisition, we recognized two transactions as separate and apart from the business combination with Mt. Holly. The Mt. Holly smelter tolled alumina for its partners and so had no alumina supply of its own. Upon the purchase, we negotiated with Alcoa to purchase alumina under two separate alumina supply agreements. We believe the price paid under these agreements was equivalent to a market rate that would be paid by a market participant. Contract prices were based on published alumina price indexes. In addition, we had a pre-existing relationship with Alcoa prior to the acquisition of Mt. Holly. Mt. Holly had receivables due from Alcoa's subsidiary, Alumax, that were part of the normal operations of the business. We assessed that these receivables were effectively settled as a result of the acquisition and were accounted for separately from the business combination. The receivables will be settled at an amount calculated consistent with the practices of Mt. Holly. The amounts due from Alumax are identified in the table above and recorded in the consolidated financial statements in accrued and other current liabilities as an offset against amounts due to Alcoa.
	Amounts Recognized Separately from the Acquisition:	Line item	Amount recognized
	Amounts Due from Alumax	Accrued and other current liabilities	$	20,786
	Alumina Supply Agreements	Inventory	14,880
	Acquisition of Sebree aluminum smelter
	On June 1, 2013, Century Sebree acquired the Sebree aluminum smelter from a subsidiary of RTA. Sebree, located in Robards, Kentucky, had an annual hot metal production capacity of 205,000 tonnes of primary aluminum and employed approximately 500 people as of the acquisition date. The purchase price for the acquisition was $61,000 (subject to customary working capital adjustments). As part of the transaction, RTA retained all historical environmental liabilities of the Sebree smelter and funded the pension plan assumed by Century in accordance with the purchase agreement.
	Working Capital Adjustment
	In July 2014, we reached the final determination of the working capital adjustments for the Sebree acquisition, resulting in a final purchase price of $49,035. As the final determination was subsequent to the expiration of measurement period defined under ASC 805, we recognized a gain of approximately $965 in the second quarter of 2014 (these adjustments were not included as part of the gain on bargain purchase recorded in 2013). The gain was recorded in other income – net, from the release of accrued amounts related to the acquisition.
	Purchase Price Allocation
	Allocating the purchase price to the acquired assets and liabilities involves management judgment. We allocated the purchase price in accordance with ASC 805 using the estimated fair values at the date of acquisition. Based on the final purchase price allocation, we recorded a gain on bargain purchase of $5,253 in 2013.
	The following table summarizes the fair value of the assets acquired and the liabilities assumed as of the acquisition date:
		Acquisition Date Fair Value
Consideration:
Cash	$	48,083
Deferred purchase price	1,910
Assets Acquired:
Inventories	$	59,018
Prepaid and other current assets	2,273
Property, plant and equipment – net	55,520
Total assets acquired	$	116,811
Liabilities Assumed:
Accrued and other current liabilities	$	43,316
Accrued pension benefit costs	996
Accrued postretirement benefit costs	6,544
Other liabilities	7,476
Deferred taxes	3,233
Total liabilities assumed	$	61,565
Gain on bargain purchase:	$	5,253
From the acquisition date of June 1, 2013 through December 31, 2013, the revenue and earnings that were attributable to Sebree included in the consolidated statement of operations is as follows:
	Year ended December 31, 2013
Sebree revenue	$	247,178
Sebree income from continuing operations (1)	8,705
-1	Our net income for the years ended December 31, 2014 and 2013, includes a non-recurring credit for the amortization of the deferred power contract liability of $5,534 and $31,031, respectively, related to the amortization of an unfavorable power contract assumed as part of the Sebree acquisition resulting in a credit to our depreciation and amortization expense within cost of goods sold on the consolidated statement of operations for the first quarter of 2014. The power contract terminated on January 31, 2014.
The following unaudited pro forma financial information for the year ended December 31, 2013 reflects our results of continuing operations as if the acquisition of Sebree had been completed on January 1, 2012. This unaudited pro forma financial information is provided for informational purposes only and is not necessarily indicative of what the actual results of operations would have been had the transactions taken place on January 1, 2012, nor is it indicative of the future consolidated results of operations or financial position of the combined companies.
	Year ended December 31,
	2013			2012
Pro forma revenues	$	1,662,707		$	1,755,196
Pro forma loss from continuing operations	(83,035		)	(260,505		)
Pro forma loss per common share, basic	(0.94		)	(2.94		)
Pro forma loss per common share, diluted	(0.94		)	(2.94		)

Asset_purchase

Asset purchase	12 Months Ended
	Dec. 31, 2014
Asset Acquisition [Abstract]
Asset purchase	Asset purchase
	In June 2012, Century Vlissingen purchased substantially all of the assets of a carbon anode production facility located in Vlissingen, the Netherlands for approximately $12,500. In connection with the purchase, we entered into a ground lease with respect to the facility that is renewable at our option. Century Vlissingen did not assume, and is indemnified by the seller against, historical liabilities of the facility.
	Following the acquisition, we have undertaken a significant capital investment to modernize the facility, comply with environmental regulations and optimize anode production for our smelter in Grundartangi. Vlissingen restarted production in late 2013 with an initial annual carbon anode production capacity of 75,000 tonnes. In the third quarter of 2014, we began a project to restart the second baking furnace, which is expected to increase total annual production capacity to 150,000 tonnes. The project is currently expected to be completed by the end of 2015.

Fair_value_measurements

Fair value measurements	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair value measurements	Fair value measurements
	ASC 820 defines fair value, establishes a framework for measuring fair value and expands disclosures about fair value measurements.  This pronouncement applies to a broad range of other existing accounting pronouncements that require or permit fair value measurements.  ASC 820 defines fair value as "the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date."  Fair value is an exit price and that exit price should reflect all the assumptions that market participants would use in pricing the asset or liability.
	ASC 820 recognizes three valuation techniques: the market approach, income approach, and cost approach.  Valuation techniques used for fair value measurements are based upon observable and unobservable inputs.  Observable inputs reflect market data obtained from independent sources, while unobservable inputs reflect our internal market assumptions.  These two types of inputs create the following fair value hierarchy:
	•	Level 1 – Valuations are based on quoted prices for identical assets or liabilities in an active market.
	•	Level 2 – Valuations are based on quoted prices for similar assets or liabilities in active markets; quoted prices for identical or similar assets or liabilities in markets that are not active; and model-derived valuations for which all significant inputs are observable or can be corroborated by observable market data.
	•	Level 3 – Assets or liabilities whose significant inputs are unobservable.  Valuations are determined using pricing models and discounted cash flow models and include management judgment and estimation which may be significant.
	The following section describes the valuation methodology used to measure our financial assets and liabilities that were accounted for at fair value.
	Overview of Century’s valuation methodology
		Level	Significant inputs
	Cash equivalents	1	Quoted market prices
	Trust assets (1)	1	Quoted market prices
	Surety bonds	1	Quoted market prices
	E.ON contingent obligation	3	Quoted LME forward market, management’s estimates of the LME forward market prices for periods beyond the quoted periods and management’s estimate of future level of operations at CAKY
	Primary aluminum sales contract	3	Management’s estimates of future U.S. Midwest premium and risk-adjusted discount rates
	Midwest premium contracts	3	Management’s estimates of future U.S. Midwest premium
	-1	Trust assets are currently invested in money market funds. These trust assets are held to fund the non-qualified supplemental executive pension benefit obligations for certain of our officers.  The trust has sole authority to invest the funds in secure interest producing investments consisting of short-term securities issued or guaranteed by the United States government or cash and cash equivalents.
	Fair value measurements
	Our fair value measurements include the consideration of market risks that other market participants might consider in pricing the particular asset or liability, specifically non-performance risk and counterparty credit risk.  Considerations of the non-performance risk and counterparty credit risk are used to establish the appropriate risk-adjusted discount rates used in our fair value measurements.
	The following table sets forth our financial assets and liabilities that were accounted for at fair value on a recurring basis by the level of input within the ASC 820 fair value hierarchy.  As required by GAAP for fair value measurements and disclosures, financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement.  Our assessment of the significance of a particular input to the fair value measurement requires judgment, and may affect the valuation of fair value assets and liabilities and the placement within the fair value hierarchy levels. There were no transfers between Level 1 and 2 during the periods presented. There were no transfers into or out of Level 3 during the periods presented. It is our policy to recognize transfers into and transfers out of Level 3 as of the actual date of the event or change in circumstances that caused the transfer.
	Recurring Fair Value Measurements	As of December 31, 2014
		Level 1			Level 2			Level 3		Total
	ASSETS:
	Cash equivalents	$	137,712		$	—		$	—	$	137,712
	Trust assets	8,067			—			—		8,067
	Surety bonds	1,987			—			—		1,987
	TOTAL	$	147,766		$	—		$	—	$	147,766
	LIABILITIES:
	E.ON contingent obligation – net (1)	$	—		$	—		$	—	$	—
	TOTAL	$	—		$	—		$	—	$	—
	Recurring Fair Value Measurements	As of December 31, 2013
		Level 1			Level 2			Level 3		Total
	ASSETS:
	Cash equivalents	$	49,658		$	—		$	—	$	49,658
	Trust assets	11,151			—			—		11,151
	Surety bonds	2,002			—			—		2,002
	Midwest premium contracts	—			—			140		140
	TOTAL	$	62,811		$	—		$	140	$	62,951
	LIABILITIES:
	E.ON contingent obligation – net (1)	$	—		$	—		$	—	$	—
	Primary aluminum sales contract	—			—			140		140
	TOTAL	$	—		$	—		$	140	$	140
	-1	See Note 6 Debt for additional information about the E.ON contingent obligation.
	Change in Level 3 Fair Value Measurements during the years ended December 31,
		Derivative liabilities - net
		2014			2013
	Beginning balance, January 1,	$	—		$	(16,539	)
	Total gain (loss) included in earnings	(940		)	16,539
	Settlements	940			—
	Ending balance, December 31,	$	—		$	—
	Amount of gain included in earnings attributable to the change in unrealized losses relating to assets and liabilities held at December 31,	$	—		$	16,539
	The net gain (loss) on our derivative assets and liabilities is recorded in our consolidated statements of operations under net gain (loss) on forward and derivative contracts.  See Note 5 Derivative and hedging instruments for the location of our Level 3 derivative assets and liabilities within our consolidated balance sheets.
	Certain Financial Instruments
	Certain of our financial instruments are reported at their carrying amount. We disclose the fair value measurements of our financial instruments which are reported at carrying amount. See Note 1 Summary of significant accounting policies for information about these financial instruments. The fair value of our 7.5% Notes due 2021 and our 7.5% Notes due 2014 was measured based on the latest available trading data as of the date presented. Although we use quoted market prices for identical debt instruments, the markets on which they trade are not considered active and are therefore considered Level 2 fair value measurements.

Derivative_and_hedging_instrum

Derivative and hedging instruments	12 Months Ended
	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative and hedging instruments	Derivative and hedging instruments
	Derivatives.  Our current derivative contracts include the E.ON contingent obligation.  See Note 4 Fair value measurements for additional information about the fair value measurements of our derivative instruments. The following table provides the fair value and balance sheet classification of our derivatives:
	Fair Value of Derivative Assets and Liabilities
			December 31,
		Balance sheet location	2014			2013
	DERIVATIVE ASSETS:
	Midwest premium contracts	Prepaid and other current assets	$	—		$	140
	TOTAL		$	—		$	140
	DERIVATIVE LIABILITIES:
	Primary aluminum sales contract	Accrued and other current liabilities	$	—		$	140
	E.ON contingent obligation - net (1)	Other liabilities	—			—
	TOTAL		$	—		$	—
	-1	See Note 6 Debt for additional information about the E.ON contingent obligation.
	Midwest premium contracts
	We entered into a fixed-price forward contract that settled monthly from January 2014 to March 2014 based on the Midwest premium price published in the Platts Metals Week for the applicable period. Losses associated with the settlements of the U.S. Midwest premium contracts were recorded in net gain (loss) on forward and derivative contracts on the consolidated statement of operations.
	Primary aluminum sales contract
	We had a contract to sell to Glencore primary aluminum produced at Mt. Holly, Hawesville and Sebree through December 31, 2013 (the "Glencore Metal Agreement"). The Glencore Metal Agreement was a physical delivery contract for primary aluminum with variable, LME-based pricing.  Under the Glencore Metal Agreement, pricing was based on market prices, adjusted by a negotiated U.S. Midwest premium with a cap and a floor as applied to the current U.S. Midwest premium.  We accounted for the Glencore Metal Agreement as a derivative instrument under ASC 815 "Derivatives and Hedging."  Gains and losses on the derivative were based on the difference between the contracted U.S. Midwest premium and actual and forecasted U.S. Midwest premiums.  Settlements were recorded in related party sales.  Unrealized gains (losses) based on forecasted U.S. Midwest premiums were recorded in net gain (loss) on forward and derivative contracts on the consolidated statements of operations.
	Derivatives not designated as hedging instruments:
		Gain (loss) recognized in income from derivatives
		Location	December 31, 2014			December 31, 2013
	E.ON contingent obligation – net	Net gain (loss) on forward and derivative contracts	$	1,412		$	16,781
	Primary aluminum sales contract	Related party sales	292			1,353
	Midwest premium contracts	Net gain (loss) on forward and derivative contracts	(1,080		)	140
	Primary aluminum sales contract	Net gain (loss) on forward and derivative contracts	(153		)	(323		)
	E.ON contingent obligation - net	Interest expense	(1,412		)	(1,412		)
	We had the following outstanding forward contracts that were not designated as hedging instruments:
		December 31, 2014		December 31, 2013
	Primary aluminum sales contract premium (tonnes) (1)	—		1,782
	Midwest premium contracts (tonnes)	—		6,000
	-1	Represents the remaining physical deliveries under the Glencore Metal Agreement.
	Counterparty credit risk.  Forward financial contracts are subject to counterparty credit risk.  However, we only enter into forward financial contracts with counterparties we determine to be creditworthy at the time of entering into the contract.  If any counterparty failed to perform according to the terms of the contract, the impact would be limited to the difference between the contract price and the market price applied to the contract volume on the date of settlement.

Debt

Debt	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Debt	Debt
		December 31,
		2014			2013
	Debt classified as current liabilities:
	Hancock County industrial revenue bonds ("IRBs") due 2028, interest payable quarterly (variable interest rates (not to exceed 12%)) (1)	$	7,815		$	7,815
	7.5% senior unsecured notes due August 15, 2014, interest payable semiannually (2)(3)	—			2,603
	Iceland revolving credit facility (3)(4)	—			6,000
	Debt classified as non-current liabilities:
	7.5% senior secured notes due June 1, 2021, net of debt discount of $3,112 and $3,472, respectively, interest payable semiannually	246,888			246,528
	Total	$	254,703		$	262,946
	-1	The IRBs are classified as current liabilities because they are remarketed weekly and could be required to be repaid upon demand if there is a failed remarketing. The IRB interest rate at December 31, 2014 was 0.24%.
	-2	The amount outstanding was repaid upon maturity.
	-3	These items are recorded in accrued and other current liabilities based on the repayment terms and expected maturity.
	-4	Borrowings under the Iceland revolving credit facility bear variable interest based on LIBOR plus the applicable margin per annum. The interest rate at December 31, 2013 was 3.92%.
	U.S. Revolving Credit Facility
	General.  We and certain of our direct and indirect domestic subsidiaries (together with Century, the "Borrowers") and Wells Fargo Capital Finance, LLC, as lender and agent, and Credit Suisse AG, BNP Paribas and Morgan Stanley Senior Funding Inc., as lenders, are parties to the Amended and Restated Loan and Security Agreement (the "U.S. revolving credit facility"), dated May 24, 2013, as amended. The U.S. revolving credit facility has a term through May 24, 2018 and provides for borrowings of up to $150,000 in the aggregate, including up to $130,000 under a letter of credit sub-facility.  Any letters of credit issued and outstanding under the U.S. revolving credit facility reduce our borrowing availability on a dollar-for-dollar basis.
	Status of our U.S. revolving credit facility:
		December 31, 2014
	Credit facility maximum amount	$	150,000
	Borrowing availability, net of outstanding letters of credit	38,617
	Outstanding borrowings	—
	Letter of credit sub-facility amount (1)	130,000
	Outstanding letters of credit issued	111,383
	-1	In connection with the acquisition of Mt. Holly, the U.S. revolving credit facility was amended to increase the letter of credit sub-facility from $80,000 to $100,000. On December 1, 2014, we entered into an additional amendment to the U.S. revolving credit facility, increasing our letter of credit sub-facility to $130,000 for the period from December 1, 2014 through March 1, 2015.
	Borrowing Base.  The availability of funds under the U.S. revolving credit facility is limited by a specified borrowing base consisting of accounts receivable and inventory of the Borrowers which meet the eligibility criteria.
	Guaranty.  The Borrowers' obligations under the U.S. revolving credit facility are guaranteed by certain of our domestic subsidiaries and secured by a continuing lien upon and a security interest in all of the Borrowers' accounts receivable, inventory and certain bank accounts.  Each Borrower is liable for any and all obligations under the U.S. revolving credit facility on a joint and several basis.
	Interest Rates and Fees.  Any amounts outstanding under the U.S. revolving credit facility will bear interest, at our option, at LIBOR or a base rate, plus, in each case, an applicable interest margin.  The applicable interest margin is determined based on the average daily availability for the immediately preceding quarter.  In addition, we pay an unused line fee on undrawn amounts, less the amount of our letters of credit exposure. For standby letters of credit, we are required to pay a fee on the face amount of such letters of credit that varies depending on whether the letter of credit exposure is cash collateralized.
	Prepayments.  We can make prepayments of amounts outstanding under the U.S. revolving credit facility, in whole or in part, without premium or penalty, subject to standard LIBOR breakage costs, if applicable.  We may be required to apply the proceeds from sales of collateral accounts, other than sales of inventory in the ordinary course of business, to repay amounts outstanding under the revolving credit facility and correspondingly reduce the commitments there under.
	Covenants.  The U.S. revolving credit facility contains customary covenants, including restrictions on mergers and acquisitions, indebtedness, affiliate transactions, liens, dividends and distributions, dispositions of collateral, investments and prepayments of indebtedness, as well as a covenant that requires the Borrowers to maintain certain minimum liquidity or availability requirements.
	Events of Default.  The U.S. revolving credit facility also includes customary events of default, including nonpayment, misrepresentation, breach of covenant, bankruptcy, change of ownership, certain judgments and certain cross defaults. Upon the occurrence of an event of default, commitments under the U.S. revolving credit facility may be terminated and amounts outstanding may be accelerated and declared immediately due and payable.
	Iceland Revolving Credit Facility
	General. Nordural Grundartangi ehf, as borrower, and Landsbankinn hf., as lender, entered into a $50,000 Committed Revolving Credit Facility agreement (the "Iceland revolving credit facility"), dated November 27, 2013. Grundartangi may in the future use the Iceland revolving credit facility to repay existing indebtedness or to finance capital expenditures and for ongoing working capital needs and other general corporate purposes. Under the terms of the Iceland revolving credit facility, when Grundartangi borrows funds it will designate a repayment date, which may be any date prior to the maturity of the Iceland revolving credit facility. The Iceland revolving credit facility has a term through November 27, 2016.
	Status of our Iceland revolving credit facility:
		December 31, 2014
	Credit Facility maximum amount	$	50,000
	Borrowing availability	49,940
	Outstanding borrowings	—
	Borrowing Base.  The availability of funds under the Iceland revolving credit facility is limited by a specified borrowing base consisting of inventory and accounts receivable of Grundartangi.
	Security.  Grundartangi's obligations under the Iceland revolving credit facility are secured by a general bond under which Grundartangi's inventory and accounts receivable are pledged to secure full payment of the loan.
	Interest Rates and Fees.  Any amounts outstanding under the Iceland revolving credit facility will bear interest at LIBOR plus the margin per annum.
	Prepayments.  Grundartangi may, by giving no less than five business days prior written notice to Landsbankinn, prepay any outstanding borrowings without penalty or premium (except incurred breakage costs) in whole or in part.
	Covenants.  The Iceland revolving credit facility contains customary covenants, including restrictions on mergers and acquisitions, dispositions of assets, compliance with permits, laws and payment of taxes, as well as a covenant that requires Grundartangi to maintain a certain minimum equity ratio.
	Events of Default.  The Iceland revolving credit facility also includes customary events of default, including nonpayment, loss of license, cessation of operations, unlawfulness, breach of covenant, bankruptcy, change of ownership, certain judgments and certain cross defaults. Upon the occurrence of an event of default, commitments under the Iceland revolving credit facility may be terminated and amounts outstanding may be accelerated and declared immediately due and payable.
	8% Notes Tender Offer, Consent Solicitation and Redemption
	In May 2013, we commenced a tender offer and consent solicitation (the "Tender Offer") to the holders of our then outstanding 8% Senior Secured Notes due 2014 (the "8.0% Notes"). Investors electing to participate in the Tender Offer consented to certain amendments and modifications to the indenture governing the 8.0% Notes to remove, among other things, most of the restrictive covenants, in exchange for which we paid these investors consent fees.
	We received tenders and consents from holders of a majority of the outstanding principal amount of the 8.0% Notes. The remaining 8.0% Notes outstanding that had not participated in the Tender Offer were redeemed at a redemption price of 100% of the principal amount thereof, plus accrued and unpaid interest (the "Redemption"). Together the Tender Offer and Redemption satisfied and discharged our obligations under the 8.0% Notes and the related indenture. We used the net proceeds from the issuance of the 7.5% Senior Secured Notes due 2021 (the "7.5% Notes due 2021") and available cash on hand to fund the Tender Offer and the Redemption.  As of December 31, 2014 and 2013, we had no principal amounts outstanding on the 8% Notes.
	In accordance with ASC 470 "Debt", based on an evaluation of the characteristics of the 8.0% Notes and the 7.5% Notes due 2021 that were issued, we treated the tender and redemption of the 8.0% Notes as an extinguishment of the debt and accordingly, we recorded a loss on early extinguishment of debt in 2013. The loss on early extinguishment of debt consisted of the write-off of deferred financing costs and the debt discount associated with the 8.0% Notes, as well as the tender premium paid as part of the Tender Offer.
	7.5% Notes due 2021
	General.  On June 4, 2013, we issued $250,000 of our 7.5% Notes due 2021 in a private offering exempt from the registration requirements of the Securities Act.  The 7.5% Notes due 2021 were issued at a discount and we received proceeds of $246,330, prior to payment of financing fees and related expenses.
	Interest rate.  The 7.5% Notes due 2021 bear interest at 7.5% per annum on the principal amount, payable semi-annually in arrears in cash on June 1st and December 1st of each year.
	Maturity.  The 7.5% Notes due 2021 mature on June 1, 2021.
	Seniority.  The 7.5% Notes due 2021 are senior secured obligations of Century, ranking equally in right of payment with all existing and future senior indebtedness of Century, but effectively senior to unsecured debt to the extent of the value of the collateral.
	Guaranty.  Our obligations under the 7.5% Notes due 2021 are guaranteed by all of our existing and future domestic restricted subsidiaries (the "Guarantor Subsidiaries"), except for foreign owned holding companies and any domestic restricted subsidiary that owns no assets other than equity interests or other investments in foreign subsidiaries, which guaranty shall in each case be a senior secured obligation of such Guarantor Subsidiaries, ranking equally in right of payment with all existing and future senior indebtedness of such Guarantor Subsidiaries but effectively senior to unsecured debt.
	Collateral. Our obligations under the 7.5% Notes due 2021 and the Guarantor Subsidiaries' obligations under the guarantees are secured by a pledge of and lien on (subject to certain exceptions):
	(i)	all of our and the Guarantor Subsidiaries' property, plant and equipment;
	(ii)	all equity interests in domestic subsidiaries directly owned by us and the Guarantor Subsidiaries and 65% of equity interests in foreign subsidiaries or foreign holding companies directly owned by us and the Guarantor Subsidiaries;
	(iii)	intercompany notes owed by any non-guarantor to us or any Guarantor Subsidiary to us; and
	(iv)	proceeds of the foregoing.
	Under certain circumstances, we may incur additional debt that also may be secured by liens on the collateral that are equal to or have priority over the liens securing the 7.5% Notes due 2021.
	Redemption Rights.  Prior to June 1, 2016, we may redeem the 7.5% Notes due 2021, in whole or in part, at a redemption price equal to 100% of the principal amount plus a make-whole premium, and if redeemed during the twelve-month period beginning on June 1 of the years indicated below, at the following redemption prices plus accrued and unpaid interest:
	Year	Percentage
	2016	105.62%
	2017	103.75%
	2018	101.88%
2019 and thereafter	100.00%
Upon a change of control (as defined in the indenture governing the 7.5% Notes due 2021), we will be required to make an offer to purchase the 7.5% Notes due 2021 at a purchase price equal to 101% of the outstanding principal amount of the 7.5% Notes due 2021 on the date of the purchase, plus accrued interest to the date of purchase.
Covenants.  The indenture governing the 7.5% Notes due 2021 contains customary covenants which may limit our ability, and the ability of certain of our subsidiaries, to: (i) incur additional debt; (ii) incur additional liens; (iii) pay dividends or make distributions in respect of capital stock; (iv) purchase or redeem capital stock; (v) make investments or certain other restricted payments; (vi) sell assets; (vii) issue or sell stock of certain subsidiaries; (viii) enter into transactions with shareholders or affiliates; and (ix) effect a consolidation or merger.
7.5% Notes due 2014
General.  In August 2004, we sold $250,000 of our 7.5% Notes due 2014 in a private offering exempt from the registration requirements of the Securities Act.  The 7.5% Notes due 2014 were subsequently registered with the SEC in December 2004.
Exchange offer and consent solicitation.  In 2010 and 2009, we completed a series of debt for debt exchange offers and consent solicitation relating to our 7.5% Notes (the "7.5% Notes Exchange Offer") in which we issued our 8.0% Notes in exchange for our 7.5% Notes due 2014.  In addition, certain investors consented to certain amendments and modifications to the indenture governing the 7.5% Notes due 2014 to remove, among other things, most of the restrictive covenants, in exchange for which we paid these investors consent fees.  The 7.5% Notes due 2014 matured on August 15, 2014 and was repaid upon maturity.
E.ON contingent obligation
General.  The E.ON contingent obligation consists of the aggregate E.ON payments made to Big Rivers Electric Corporation ("Big Rivers") on CAKY’s behalf in excess of the agreed upon base amount under the long-term cost-based power contract with Kenergy, a member cooperative of Big Rivers (the "Big Rivers Agreement").  Our obligation to make repayments is contingent upon certain operating criteria for Hawesville and the LME price of primary aluminum.  When the conditions for repayment are met, and for so long as those conditions continue to be met, we will be obligated to make principal and interest payments, in up to 72 monthly payments.
Based on the LME forward market prices for primary aluminum at December 31, 2014 and management's estimate of the LME forward market for periods beyond the quoted periods, we recognized a derivative asset which offsets our contingent obligation. As a result, our net liability decreased and we recorded a gain of $1,412 and $16,781 in net gain (loss) on forward and derivative contracts for the years ended December 31, 2014 and 2013. In addition, we believe that we will not have any payment obligations for the E.ON contingent obligation through the term of the agreement, which expires in 2028. However, future increases in the LME forward market may result in a partial or full derecognition of the derivative asset and a corresponding recognition of a loss.
Interest rate.  Interest accrues at an annual rate equal to 10.94%.
Maturity.  The term of the agreement is through December 31, 2028.
The following table provides information about the balance sheet location and gross amounts offset:
Offsetting of financial instruments and derivatives
	Balance sheet location	31-Dec-14			31-Dec-13
E.ON contingent obligation – principal	Other liabilities	$	(12,902	)	$	(12,902	)
E.ON contingent obligation – accrued interest	Other liabilities	(5,291		)	(3,879		)
E.ON contingent obligation – derivative asset	Other liabilities	18,193			16,781
		$	—		$	—
Industrial Revenue Bonds
General.  As part of the purchase price for our acquisition of the Hawesville facility, we assumed industrial revenue bonds which were issued in connection with the financing of certain solid waste disposal facilities constructed at the Hawesville facility.
Interest rate.  The IRBs bear interest at a variable rate not to exceed 12% per annum determined weekly based upon prevailing rates for similar bonds in the industrial revenue bond market. Interest on the industrial revenue bonds is paid quarterly.
Maturity.  The industrial revenue bonds mature on April 1, 2028.
Security.  The industrial revenue bonds are secured by a letter of credit issued under our revolving credit facility.
Principal Payments on Long Term Debt
We have no principal payments due in the next five years for our long-term borrowings.

Shareholders_equity

Shareholders' equity	12 Months Ended
	Dec. 31, 2014
Stockholders' Equity Note [Abstract]
Shareholders' equity	Shareholders' equity
	Common Stock
	Under our Restated Certificate of Incorporation, our Board of Directors is authorized to issue up to 195,000,000 shares of our common stock.
	The rights, preferences and privileges of holders of our common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any series of our preferred stock which are currently outstanding, including our Series A Convertible Preferred Stock, or which we may designate and issue in the future.
	Preferred Stock
	Under our Restated Certificate of Incorporation, our Board of Directors is authorized to issue up to 5,000,000 shares of preferred stock.  Our Board of Directors may issue preferred stock in one or more series and determine for each series the dividend rights, conversion rights, voting rights, redemption rights, liquidation preferences, sinking fund terms and the number of shares constituting that series, as well as the designation thereof.  Depending upon the terms of preferred stock established by our Board of Directors, any or all of the preferred stock could have preference over the common stock with respect to dividends and other distributions and upon the liquidation of Century. In addition, issuance of any shares of preferred stock with voting powers may dilute the voting power of the outstanding common stock.
	Series A Convertible Preferred Stock
	Shares Authorized and Outstanding.  In 2008, we issued 160,000 shares of our Series A Convertible Preferred Stock.  Glencore holds all of the issued and outstanding Series A Convertible Preferred Stock.
	The issuance of common stock under our stock incentive programs, debt exchange transactions and any stock offering that excludes Glencore participation triggers anti-dilution provisions of the preferred stock agreement and results in the automatic conversion of Series A Convertible Preferred Stock shares into shares of common stock.  Our Series A Convertible Preferred Stock has a par value of $0.01 per share.
	The Common and Preferred Stock Activity table below contains additional information about preferred stock conversions during 2014, 2013 and 2012:
	Common and Preferred Stock Activity:	Preferred stock		Common stock
	(in shares)	Series A convertible		Treasury	Outstanding
	Balance as of December 31, 2011	80,718		4,386,521	88,844,327
	Repurchase of common stock	—		400,000	(400,000	)
	Conversion of convertible preferred stock	(435	)	—	43,556
	Issuance for share-based compensation plans	—		—	60,754
	Balance as of December 31, 2012	80,283		4,786,521	88,548,637
	Conversion of convertible preferred stock	(663	)	—	66,244
	Issuance for share-based compensation plans	—		—	95,396
	Balance as of December 31, 2013	79,620		4,786,521	88,710,277
	Conversion of convertible preferred stock	(1,479	)	—	147,952
	Issuance for share-based compensation plans	—		—	206,353
	Balance as of December 31, 2014	78,141		4,786,521	89,064,582
	Dividend Rights.  So long as any shares of our Series A Convertible Preferred Stock are outstanding, we may not pay or declare any dividend or make any distribution upon or in respect of our common stock or any other capital stock ranking on a parity with or junior to the Series A Convertible Preferred Stock in respect of dividends or liquidation preference, unless we, at the same time, declare and pay a dividend or distribution on the shares of Series A Convertible Preferred Stock (a) in an amount equal to the amount such holders would receive if they were the holders of the number of shares of our common stock into which their shares of Series A Convertible Preferred Stock are convertible as of the record date fixed for such dividend or distribution, or (b) in the case of a dividend or distribution on other capital stock ranking on a parity with or junior to the Series A Convertible Preferred Stock in such amount and in such form as (based on the determination of holders of a majority of the Series A Convertible Preferred Stock) will preserve, without dilution, the economic position of the Series A Convertible Preferred Stock relative to such other capital stock.
	Voting Rights.  The Series A Convertible Preferred Stock has no voting rights for the election of directors or on other matters where the shares of common stock have voting rights.  However, we may not change the powers, preferences, or rights given to the Series A Convertible Preferred Stock, or authorize, create or issue any additional shares of Series A Convertible Preferred Stock without the affirmative vote of the holders of a majority of the shares of Series A Convertible Preferred Stock then outstanding (voting separately as a class).
	Liquidation Rights.  Upon any liquidation, dissolution, or winding-up of Century, the holders of shares of Series A Convertible Preferred Stock are entitled to receive a preferential distribution of $0.01 per share out of the assets available for distribution.  In addition, upon any liquidation, dissolution or winding-up of Century, if our assets are sufficient to make any distribution to the holders of the common stock, then the holders of shares of Series A Convertible Preferred Stock are also entitled to share ratably with the holders of common stock in the distribution of Century’s assets (as though the holders of Series A Convertible Preferred Stock were holders of that number of shares of common stock into which their shares of Series A Convertible Preferred Stock are convertible).  However, the amount of any such distribution will be reduced by the amount of the preferential distribution received by the holders of the Series A Convertible Preferred Stock.
	Transfer Restrictions.  Glencore is prohibited from transferring shares of Series A Convertible Preferred Stock to any party other than an affiliate who agrees to become bound by certain agreements associated with these shares.
	Automatic Conversion.  The Series A Convertible Preferred Stock automatically converts, without any further act of Century or any holders of Series A Convertible Preferred Stock, into shares of common stock, at a conversion ratio of 100 shares of common stock for each share of Series A Convertible Preferred Stock, upon the occurrence of any of the following automatic conversion events:
	•	If we sell or issue shares of common stock or any other stock that votes generally with our common stock, or the occurrence of any other event, including a sale, transfer or other disposition of common stock by Glencore, as a result of which the percentage of voting stock held by Glencore decreases, an amount of Series A Convertible Preferred Stock will convert to common stock to restore Glencore to its previous ownership percentage;
	•	If shares of Series A Convertible Preferred Stock are transferred to an entity that is not an affiliate of Glencore, such shares of Series A Convertible Preferred Stock will convert to shares of our common stock, provided that such transfers may only be made pursuant to an effective registration statement;
	•	Upon a sale of Series A Convertible Preferred Stock by Glencore in a Rule 144 transaction in which the shares of Series A Convertible Preferred Stock and our common stock issuable upon the conversion thereof are not directed to any purchaser, such shares of Series A Convertible Preferred Stock sold will convert to shares of our common stock; and
	•	Immediately prior to and conditioned upon the consummation of a merger, reorganization or consolidation to which we are a party or a sale, abandonment, transfer, lease, license, mortgage, exchange or other disposition of all or substantially all of our property or assets, in one or a series of transactions where, in any such case, all of our common stock would be converted into the right to receive, or exchanged for, cash and/or securities, other than any transaction in which the Series A Convertible Preferred Stock will be redeemed.
	Optional Conversion.  Glencore has the option to convert the Series A Convertible Preferred Stock in a tender offer or exchange offer, at the same conversion ratio as above, in which a majority of the outstanding shares of our common stock have been tendered by the holders thereof and not duly withdrawn at the expiration time of such tender or exchange offer, so long as the Series A Convertible Preferred Stock is tendered or exchanged in such offer.
	Stock Combinations – Adjustments.  If, at any time while the Series A Convertible Preferred Stock is outstanding, Century combines outstanding common stock into a smaller number of shares, then the number of shares of common stock issuable on conversion of each share of Series A Convertible Preferred Stock will be decreased in proportion to such decrease in the aggregate number of shares of common stock outstanding.
	Redemptions or Repurchases of Common Stock.  We may not redeem or repurchase our common stock unless we redeem or repurchase, or otherwise make a payment on, a pro rata number of shares of the Series A Convertible Preferred Stock.  These restrictions do not apply to our open market repurchases or our repurchases pursuant to our employee benefit plans.
	Right of Redemption.  The Series A Convertible Preferred Stock will be redeemed by Century if any of the following events occur (at a redemption price based on the trading price of our common stock prior to the announcement of such event) and Glencore votes its shares of our common stock in opposition to such events:
	•	We propose a merger, reorganization or consolidation, sale, abandonment, transfer, lease, license, mortgage, exchange or other disposition of all or substantially all of our property or assets where any of our common stock would be converted into the right to receive, or exchanged for, assets other than cash and/or securities traded on a national stock exchange or that are otherwise readily marketable, or
	•	We propose to dissolve and wind up operations and any assets, other than cash and/or securities traded on a national stock exchange or that are otherwise readily marketable, are to be distributed to the holders of our common stock.
	Stock Repurchase Program
	In August 2011, our Board of Directors approved a stock repurchase program.  Under the program, we may repurchase up to $60,000 of our outstanding shares of common stock from time to time on the open market at prevailing market prices, in block trades or otherwise. The timing and amount of any shares repurchased is determined by our management based on its evaluation of market conditions, the trading price of the stock and other factors. The repurchase program may be expanded, suspended or discontinued at any time.
	Shares of common stock repurchased are recorded at cost as treasury stock and result in a reduction of shareholders’ equity in the consolidated balance sheets. From time to time, treasury shares may be reissued as contributions to our employee benefit plans and for the conversion of convertible preferred stock. When shares are reissued, we use an average cost method for determining cost. The difference between the cost of the shares and the reissuance price is added to or deducted from additional paid-in capital.
	From August 11, 2011 through December 31, 2014, we repurchased 4,786,521 shares of common stock for an aggregate purchase price of $49,924. We have made no repurchases since March 2012 and had approximately $10,076 remaining under the repurchase program authorization as of December 31, 2014. See Note 22 Subsequent events for information about share repurchases and additional authorization amounts approved in 2015.

Inventories

Inventories	12 Months Ended
	Dec. 31, 2014
Inventory, Net [Abstract]
Inventories	Inventories
	Inventories, at December 31, consist of the following:
		2014		2013
	Raw materials	$	78,599	$	69,776
	Work-in-process	33,941		22,183
	Finished goods	19,969		17,661
	Operating and other supplies	150,971		129,995
	Inventories (1)	$	283,480	$	239,615
	-1	Includes inventory acquired in connection with the Mt. Holly acquisition. See Note 2 Business acquisitions for additional information about the Mt. Holly acquisition.

Property_Plant_and_Equipment

Property, Plant, and Equipment	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Property, plant and equipment	Property, plant and equipment
	Property, plant and equipment, at December 31, consist of the following:
		2014			2013
	Land and improvements	$	51,748		$	16,021
	Buildings and improvements	403,784			340,609
	Machinery and equipment	1,395,221			1,464,532
	Construction in progress	182,393			221,101
		2,033,146			2,042,263
	Less accumulated depreciation	(741,928		)	(794,602		)
	Property, plant and equipment - net	$	1,291,218		$	1,247,661
	For the years ended December 31, 2014, 2013 and 2012, we recorded depreciation expense of $70,731, $66,570 and $62,570, respectively.
	At December 31, 2013, the cost of property, plant and equipment includes $179,702 and accumulated depreciation includes $119,275, representing our undivided interest in the property, plant and equipment comprising Mt. Holly. See Note 2 Business acquisitions for additional information about the Mt. Holly acquisition.
	In February 2009, we curtailed the operations of the Ravenswood facility.  The net carrying value of the asset group at the Ravenswood facility was approximately $45,683 at December 31, 2014.   The aggregate capital expenditures through December 31, 2014 related to the Helguvik project were approximately $147,587.

Supplemental_financial_stateme

Supplemental financial statement info	12 Months Ended
	Dec. 31, 2014
Additional financial information disclosures [Abstract]
Supplemental financial statement info	Supplemental financial statement information
	Composition of certain balance sheet accounts at December 31:
	Components of Prepaid and other current assets:	2014			2013
	Prepaid and other assets	$	19,601		$	15,051
	Income/withholding tax receivable – current	5,389			11,437
	VAT receivable	4,778			5,648
	Derivative assets	—			140
		$	29,768		$	32,276
	Components of Other assets:	2014			2013
	Investment in BHH and other equity investments	$	34,478		$	35,767
	Pension asset related to Mt. Holly	30,842			—
	Cash surrender value of life insurance and trust assets	26,636			27,857
	Maintenance and operating supplies – non-current	17,771			17,827
	Other assets	13,850			10,023
		$	123,577		$	91,474
	Components of Accrued and other current liabilities:	2014			2013
	Accrued payable to Alcoa for Mt. Holly acquisition	$	39,208		$	—
	Accrued compensation and related benefits	19,602			11,829
	Income taxes payable	14,302			6,198
	Other accrued and current liabilities	10,573			14,842
	Accrued vacation pay	9,101			9,135
	Asset retirement obligations – current	6,006			4,230
	Deferred tax liability – current	2,241			1,555
	Accrued severance pay	2,050			11,438
	Accrued bond interest	1,563			1,636
	Revolving credit facility	—			6,000
	Current portion of long-term debt	—			2,603
		$	104,646		$	69,466
	Components of Other liabilities:	2014			2013
	Asset retirement obligations – non-current	$	30,944		$	22,884
	Other liabilities	9,275			7,576
	Contingent consideration	5,837			—
	Accrued workers’ compensation cost – non-current	7,216			7,283
	E.ON contingent liability and accrued interest	—			—
		$	53,272		$	37,743
	Components of Accumulated Other Comprehensive Loss:	2014			2013
	Defined benefit plan liabilities	$	(128,664	)	$	(92,177	)
	Equity in investee other comprehensive income (1)	—			(12,650		)
	Unrealized loss on financial instruments	(1,249		)	(1,064		)
	Other comprehensive loss before income tax effect	(129,913		)	(105,891		)
	Income tax effect (2)	12,231			14,059
	Accumulated other comprehensive loss	$	(117,682	)	$	(91,832	)
	-1	The amount includes our equity in the other comprehensive income of Mt. Holly until it was acquired.
	-2	The allocation of the income tax effect to the components of other comprehensive income is as follows:
		2014			2013
	Defined benefit plan liabilities	$	12,812		$	14,256
	Equity in investee other comprehensive income	—			418
	Unrealized loss on financial instruments	(581		)	(615		)
	The following table summarizes the changes in the accumulated balances for each component of accumulated other comprehensive loss ("AOCI"):
		Defined benefit plan and other postretirement liabilities			Equity in investee other comprehensive income			Unrealized loss on financial instruments			Total, net of tax
	Balance, December 31, 2011	$	(124,948	)	$	(7,918	)	$	(1,722	)	$	(134,588	)
	Other comprehensive income (loss) before reclassifications	(16,691		)	(4,306		)	(218		)	(21,215		)
	Net amount reclassified to net loss	4,198			—			413			4,611
	Balance, December 31, 2012	(137,441		)	(12,224		)	(1,527		)	(151,192		)
	Other comprehensive income (loss) before reclassifications	56,795			(8		)	—			56,787
	Net amount reclassified to net loss	2,725			—			(152		)	2,573
	Balance, December 31, 2013	(77,921		)	(12,232		)	(1,679		)	(91,832		)
	Other comprehensive income (loss) before reclassifications	(42,926		)	(419		)	—			(43,345		)
	Net amount reclassified to net income	4,995			—			(151		)	4,844
	Elimination of equity in investee resulting from acquisition	—			12,651			—			12,651
	Balance, December 31, 2014	$	(115,852	)	$	—		$	(1,830	)	$	(117,682	)
	Reclassifications out of AOCI were included in the consolidated statements of operations as follows:
			Gains (Losses) Reclassified from AOCI to the Consolidated Statements of Operations
	AOCI Components	Location	2014			2013			2012
Defined benefit plan and other postretirement liabilities	Cost of goods sold	$	6,237		$	3,264		$	4,670
	Selling, general and administrative expenses	569			990			1,055
	Income tax expense	(1,811		)	(1,529		)	(1,527		)
	Net of tax	$	4,995		$	2,725		$	4,198
Equity in investee other comprehensive income	Cost of goods sold	$	—		$	—		$	—
	Income tax expense	(419		)	(70		)	(70		)
	Net of tax	$	(419	)	$	(70	)	$	(70	)
Unrealized loss on financial instruments	Cost of goods sold	$	(185	)	$	(186	)	$	381
	Income tax expense	34			34			32
	Net of tax	$	(151	)	$	(152	)	$	413

Pension_and_Other_Postretireme

Pension and Other Postretirement Benefits	12 Months Ended
	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Pension and other postretirement benefits disclosure	Pension and other postretirement benefits
	Pension Benefits
	We maintain noncontributory defined benefit pension plans for all of our domestic hourly and salaried employees.  For the domestic salaried employees, plan benefits are based primarily on years of service and average compensation during the later years of employment. For hourly employees, plan benefits are based primarily on a formula that provides a specific benefit for each year of service.  Our funding policy is to contribute amounts based upon actuarial and economic assumptions designed to achieve adequate funding of the projected benefit obligations and to meet the minimum funding requirements of the Employee Retirement Income Security Act 1974 ("ERISA"). Plan assets consist principally of U.S. and international equities and fixed income securities.  In addition, we maintain the SERB plan for certain current and former executive officers.  We account for these plans in accordance with ASC 715. We use a measurement date of December 31st to determine the pension and OPEB liabilities.
	Partial Freeze
	In the fourth quarter of 2014, we amended our Salaried Pension Plan to eliminate future accruals for participants who are under age 50 as of January 1, 2015. The plan was also closed to new entrants. The amendment lowered the plans' projected benefit obligations by approximately $6,600 and resulted in a $263 curtailment charge for 2014.
	Pension Settlement - Lump Sum Payout
	In the fourth quarter of 2014, we offered certain former employees with vested pension benefits a lump sum payout in an effort to reduce our long-term pension obligations. As a result, net periodic benefit cost for our pension plans increased by a settlement charge of $4,701 for 2014 and the projected benefit obligation decreased by $19,573.
	Employer contributions
	During the year ended December 31, 2014, we made contributions of approximately $5,584 to the qualified defined benefit and SERB plans we sponsor.
	PBGC settlement
	In April 2013, we entered into a settlement agreement with the Pension Benefit Guaranty Corporation ("PBGC") regarding an alleged "cessation of operations" at our Ravenswood facility as a result of the curtailment of operations at the facility.  While we do not believe that a "cessation of operations" has occurred, we reached an agreement with the PBGC to resolve the matter.  Pursuant to the terms of the agreement, we will make additional contributions (above any minimum required contributions) to our defined benefit pension plans totaling approximately $17,400 over the term of the agreement, which runs through 2016.  In 2013, we made the contributions pursuant to this agreement of approximately $6,700. The remaining contributions under this agreement are approximately $10,700, of which approximately $3,700 was scheduled to be made in 2014. Under certain circumstances, in periods of lower primary aluminum prices relative to our cost of operations, we may defer one or more of these payments, but we would be required to provide the PBGC with acceptable security for any deferred payments. In the first quarter of 2014, we elected to defer contributions for 2014 under the PBGC agreement and have provided the PBGC with the appropriate security.
	Other Postretirement Benefits (OPEB)
	In addition to providing pension benefits, we provide certain healthcare and life insurance benefits for certain domestic retired employees. We account for these plans in accordance with ASC 715-60.  ASC 715-60 requires companies to accrue the estimated cost of providing postretirement benefits during the working careers of those employees who could become eligible for such benefits when they retire. We fund these benefits as the retirees submit claims.
	Retiree medical benefits changes
	In 2012, Century Aluminum of West Virginia ("CAWV") amended its postretirement medical benefit plan for all current and former salaried employees, their dependents and all bargaining unit employees who retired before October 1, 2012, and their dependents.  Effective January 1, 2013, CAWV no longer provided retiree medical benefits to active salaried CAWV personnel or any other personnel who retired prior to October 1, 2012.  CAWV has made no commitments as to the future status of retiree medical benefits for hourly personnel who are currently covered by an active medical program.  For those retirees impacted by the changes and who have elected COBRA coverage, CAWV waived COBRA premiums through June 30, 2013.
	The 2012 plan amendment resulted in the immediate recognition of any unamortized prior service cost benefits that were accrued in accumulated other comprehensive loss as of the date of the amendments.
	Under the current Hawesville labor agreement, employees who retire during the term of the labor agreement have been divided into sub-groups based on attributes such as Medicare eligibility, hire date, age and years of service.  Levels of benefits are defined for the sub-groups and range from no substantive change from the benefits provided under the previous labor agreement to replacement of the defined retiree medical benefit program with individual health reimbursement accounts for each eligible participant.  The health reimbursement accounts will be funded by CAKY based on established rates per hour worked by each eligible participant.  Eligible participants will be able to withdraw from their health reimbursement accounts to fund their own retiree medical coverage.
	Obligations and Funded Status
	The change in benefit obligations and change in plan assets as of December 31 are as follows:
		Pension							OPEB
		2014			2013				2014			2013
	Change in benefit obligation:
	Benefit obligation at beginning of year	$	238,319		$	174,954			$	134,652		$	149,263
	Service cost	5,605			4,735				1,591			2,527
	Interest cost	11,629			8,908				6,420			5,681
	Plan amendments	(5,308		)	—				—			—
	Medicare Part D	—			—				273			—
	Actuarial loss (gain)	32,772			(21,539		)		17,669			(24,170		)
	Acquisition	84,743			82,988				2,857			6,544
	Benefits paid	(11,895		)	(11,727		)		(4,681		)	(5,193		)
	Settlements	(19,573		)	—				—			—
	Benefit obligation at end of year	$	336,292		$	238,319			$	158,781		$	134,652
		Pension							OPEB
		2014			2013				2014			2013
	Change in plan assets:
	Fair value of plan assets at beginning of year	$	199,304		$	96,234			$	—		$	—
	Actual return on plan assets	16,118			21,675				—			—
	Acquisition	115,982			81,992				—			—
	Employer contributions	5,584			11,130				4,681			5,193
	Benefits paid	(11,895		)	(11,727		)		(4,681		)	(5,193		)
	Settlements	(19,573		)	—				—			—
	Fair value of assets at end of year	$	305,520		$	199,304			$	—		$	—
		Pension							OPEB
		2014			2013				2014			2013
	Funded status of plans:
	Funded status	$	(30,772	)	$	(39,015	)		$	(158,781	)	$	(134,652	)
	Amounts recognized in the Consolidated Balance Sheets:
	Non-current assets	$	30,842		$	2,547			$	—		$	—
	Current liabilities	(1,744		)	(1,714		)		(6,118		)	(5,368		)
	Non-current liabilities	(59,870		)	(39,848		)		(152,663		)	(129,284		)
	Net amount recognized	$	(30,772	)	$	(39,015	)		$	(158,781	)	$	(134,652	)
	Amounts recognized in accumulated other comprehensive loss (pre-tax):
	Net loss	$	63,360		$	45,642			$	79,720		$	65,754
	Prior service cost (benefit)	1,335			376				(15,751		)	(19,595		)
		$	64,695		$	46,018			$	63,969		$	46,159
	Our pension plans’ projected benefit obligation, accumulated benefit obligation, and fair value of plan assets as of December 31 are as follows:
		Projected Benefit Obligation							Accumulated Benefit Obligation							Fair Value of Plan assets
		2014			2013				2014			2013				2014			2013
	Sebree hourly pension plan	$	90,320		$	80,369			$	90,320		$	80,369			$	84,432		$	82,916
	CAWV hourly pension plan	61,989			66,866				61,989			66,852				55,273			64,905
	Salaried pension plan	71,017			66,686				68,247			60,870				49,367			51,483
	CASC pension plan	85,605			—				82,556			—				116,448			—
	SERB plan	27,361			24,398				25,851			23,369				—			—
	Total	$	336,292		$	238,319			$	328,963		$	231,460			$	305,520		$	199,304
The assets held in the Rabbi trust are restricted to funding the SERB plan.  However, the Rabbi trust is classified as a general asset of the company (not plan assets) and therefore, the SERB plan is considered unfunded.
Components of net periodic benefit cost and other amounts recognized in other comprehensive loss:
Net Periodic Benefit Cost:
	Year Ended December 31,
	Pension										OPEB
	2014			2013			2012				2014			2013			2012
Service cost	$	5,605		$	4,735		$	2,802			$	1,591		$	2,527		$	1,790
Interest cost	11,629			8,908			6,871				6,420			5,681			5,512
Expected return on plan assets	(14,694		)	(10,592		)	(6,962		)		—			—			—
Amortization of prior service costs	77			113			137				(3,844		)	(3,995		)	(4,250		)
Amortization of net loss	1,907			3,152			3,642				3,704			5,022			6,195
Net periodic benefit cost	4,524			6,316			6,490				7,871			9,235			9,247
Settlements	4,701			—			—				—			—			—
Curtailment cost	263			(18		)	—				—			(20		)	—
Total net periodic benefit cost	$	9,488		$	6,298		$	6,490			$	7,871		$	9,215		$	9,247
Other changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Loss (pre-tax):
	Year Ended December 31,
	Pension							OPEB
	2014			2013				2014			2013
Net loss (gain)	$	24,326		$	(32,624	)		$	17,669		$	(24,171	)
Prior service cost (benefit)	1,299			—				—			—
Amortization of net loss, including recognition due to settlement	(6,608		)	(3,152		)		(3,704		)	(5,022		)
Amortization of prior service benefit (cost), including recognition due to curtailment	(340		)	(95		)		3,844			4,015
Total amount recognized in other comprehensive loss	18,677			(35,871		)		17,809			(25,178		)
Net periodic benefit cost	9,488			6,298				7,871			9,215
Total recognized in net periodic benefit cost and other comprehensive loss	$	28,165		$	(29,573	)		$	25,680		$	(15,963	)
Amounts in accumulated other comprehensive loss expected to be recognized as components of net periodic benefit cost during 2015:
	Pension				OPEB
Amortization of net loss	$	3,601			$	4,712
Amortization of prior service cost (benefit)	99				(3,845		)
Weighted average assumptions used to determine benefit obligations at December 31:
	Pension			OPEB
	2014	2013		2014	2013
Discount rate	4.05%	4.89%		4.00%	4.99%
Rate of compensation increase (1)	3%/4%	3%/4%		3%/4%	3%/4%
Measurement date	12/31/14	12/31/13		12/31/14	12/31/13
-1	The rate of compensation increase is 3% per year for first four years and 4% per year for year five and thereafter.
Discount rate change in estimate
In 2012, we changed the approach that we use to determine the yield from the Citigroup Pension Liability Index to the Ryan Discount Rate Curve (the "Ryan Curve"). This change in the approach for determining our discount rate is considered a change in accounting estimate under ASC 250 "Accounting Changes and Error Corrections." In 2012, the discount rates determined using the Ryan Curve were approximately 25 basis points higher than those determined using the Citigroup Pension Liability Index, which lowered the plan projected benefit obligations for our pension and OPEB plans by approximately $10,000 as a result.
Weighted average assumptions used to determine net periodic benefit cost for the years ended December 31:
	Pension							OPEB
	2014		2013		2012			2014		2013		2012
Measurement date	12/31/13		12/31/12		12/31/11			12/31/13		12/31/12		12/31/11
Fiscal year end	12/31/14		12/31/13		12/31/12			12/31/14		12/31/13		12/31/12
Discount rate	4.89	%	4	%	4.25	%		4.99	%	4.01	%	3.83	%
Rate of compensation increase (1)	3%/4%		3%/4%		3%/4%			3%/4%		3%/4%		3%/4%
Expected return on plan assets	7.25	%	7.25	%	8	%		—		—		—
-1	For 2014, the rate of compensation increase is 3% per year for first four years and 4% per year for year five and thereafter. For 2013 and 2012, the rate of compensation increase is 3% per year for first five years and 4% per year for year six and thereafter.
For measurement purposes, medical cost inflation is initially estimated to be 8%, declining to 5% over seven years and thereafter.
Assumed health care cost trend rates have a significant effect on the amounts reported for the health care benefit obligations. A one-percentage-point change in the assumed health care cost trend rate would have had the following effects in 2014:
	1% Increase				1% Decrease
Effect on total of service and interest cost	$	1,258			$	(1,019	)
Effect on accumulated postretirement benefit obligation	24,815				(20,140		)
Century 401(k) Plans
We sponsor a tax-deferred savings plan under which eligible domestic employees may elect to contribute specified percentages of their compensation with Century.  We match a portion of participants' contributions to the savings plan.  Employee and matching contributions are considered fully vested immediately upon participation in the plan.
	2014			2013			2012
Company matching contribution to defined contribution (401(k)) plans	$	1,547		$	1,138		$	748
Benefit Plan Assets
Pension Plan Investment Policy and Strategy
We have established the defined benefit pension plans (the "Pension Plans") as a retirement vehicle for the plan participant employees and as a funding vehicle to secure promised benefits.  The Pension Plans’ assets are invested in a prudent manner for the exclusive purpose of providing benefits to participants. Other objectives are to:
•	Provide a total return that, over the long term, provides sufficient assets to fund the pension plan liabilities subject to a level of risk, contributions and pension expense deemed appropriate by the company.
•	Minimize, where possible, pension expense volatility, and inclusion of liability driven investing as an investment strategy when appropriate. As the funding ratio improves, the objectives will evolve to minimize the funded status volatility.
•	Diversify investments within asset classes to reduce the impact of losses in single investments.
The assets of the Pension Plans are invested in compliance with ERISA, as amended, and any subsequent applicable regulations and laws.
Performance
Our performance objective is to outperform the return of weighing passive investment alternatives by the policy target allocations after fees at a comparable level of risk. This investment objective is expected to be achieved over the long term and is measured over rolling multi-year periods. Peer-relative performance comparisons will also be considered especially when performance deviates meaningfully from market indexes. Investment objectives for each asset class are included below.
Policy Portfolio
Asset allocation policy is the principal method for achieving the Pension Plans' investment objectives stated above. The Pension Plans’ long-term strategic asset allocation policy targets are as follows:
	Pension Plan Asset Allocation
	Policy Target		December 31, 2014		December 31, 2013
Equities:
U.S. equities	50	%	42	%	43	%
International equities	15	%	18	%	20	%
Fixed income	35	%	40	%	37	%
			100	%	100	%
U.S. and international equities are held for their long-term expected return premium over fixed income investments and inflation. Fixed income is held for diversification relative to equities.
The strategic role of U.S. and international equities is to:
•	Provide higher expected returns of the major asset classes.
•	Maintain a diversified exposure within the U.S. and international stock markets through the use of multi-manager portfolio strategies.
•	Achieve returns in excess of passive indexes through the use of active investment managers and strategies.
The strategic role of fixed income is to:
•	Diversify the Pension Plans’ equity exposure by investing in fixed income securities that exhibit a low correlation to equities, thereby lowering the overall return volatility of the entire investment portfolio.
•	Maintain a diversified exposure within the U.S. fixed income market through the use of multi-manager portfolio strategies.
•	Achieve returns in excess of passive indexes through the use of active investment managers and strategies.
The long-term strategic asset allocation policy is reviewed regularly or whenever significant changes occur to Century’s or the Pension Plans' financial position and liabilities.
Expected rate-of-return assumption
We are currently using a 7.25% long-term rate of return on plan assets for the development of the net periodic cost for the defined benefit pension plans.  The rate was selected by taking into account our expected asset mix and is based on historical performance as well as expected future rates of return on plan assets.
Fair Value Measurements of Pension Plan assets
We measured the fair value of our Pension Plans’ assets in accordance with ASC 820.  For additional information about fair value measurements, see Note 4 Fair value measurements.
The following table sets forth by level within the ASC 820 fair value hierarchy our Pension Plans' assets.  As required by GAAP for fair value measurements and disclosures, these assets are classified in their entirety based on the lowest level of input that is significant to the fair value measurement.  Our assessment of the significance of a particular input to the fair value measurement requires judgment, and may affect the valuation of fair value assets and liabilities and the placement within the fair value hierarchy levels.
Fair Value of Pension Plans’ assets included under the fair value hierarchy:
As of December 31, 2014	Level 1			Level 2			Level 3			Total
Equities:
U.S. equities	$	79,148		$	—		$	—		$	79,148
International equities	33,720			—			—			33,720
Fixed income	76,204			—			—			76,204
Plan receivable (1)	—			—			116,448			116,448
Total	$	189,072		$	—		$	116,448		$	305,520
As of December 31, 2013
Equities:
U.S. equities	$	86,323		$	—		$	—		$	86,323
International equities	40,093			—			—			40,093
Fixed income	72,888			—			—			72,888
Total	$	199,304		$	—		$	—		$	199,304
-1	Represents the receivable to the Century Aluminum of South Carolina defined benefit plan related to pension funding obligations under the Stock Purchase Agreement. Amount is subject to final approval by the parties which is expected in the second quarter of 2015.
Our Pension Plans’ assets are held in certain mutual funds.  The fair value of the mutual funds is based on the Net Asset Value ("NAV") which is calculated every business day. The value of the underlying securities within the mutual funds are determined as follows:
•	U.S. listed equities; equity and fixed income options: Last sale price; last bid price if no last sale price;
•	U.S. over-the-counter equities: Official closing price; last bid price if no closing price;
•	Foreign equities: Official closing price, where available, or last sale price; last bid price if no official closing price; and
•	Municipal bonds, US bonds, Eurobonds/foreign bonds: Evaluated bid price; broker quote if no evaluated bid price.
In December 2014, we entered into the Stock Purchase Agreement to acquire Alcoa’s 50.3% stake in Mt. Holly. As part of the transaction, Alcoa and Century agreed to spinoff and fully fund a defined benefit pension plan for eligible current and former Mt. Holly employees. We established a pension plan for the Mt. Holly plan participants with a receivable for the estimated amount required to meet the benefit obligations required under the Stock Purchase Agreement. See Note 2 Business acquisitions for additional information about the pension funding requirements. The plan receivable is considered a Level 3 asset because determining the fair value requires significant unobservable inputs, including census data and various actuarial assumptions.
Our other postretirement benefit plans are unfunded. We fund these benefits as the retirees submit claims.
Pension and OPEB Cash Flows
Contributions
We expect to make the following contributions for 2015:
	2015
Expected pension plan contributions	$	5,306
Expected OPEB benefits payments	6,118
Estimated Future Benefit Payments
The following table provides the estimated future benefit payments for the pension and other postretirement benefit plans:
	Pension Benefits				OPEB Benefits
2015	$	17,487			$	6,118
2016	17,965				6,605
2017	18,191				7,212
2018	19,958				7,691
2019	19,830				8,216
2020 – 2024	97,247				43,357
Participation in Multiemployer Pension Plans
We contribute to one multiemployer defined benefit pension plan under the terms of a collective-bargaining agreement that covers our union-represented employees at Hawesville.  Currently, we do not have any plans to withdraw from or curtail participation in this plan.  The risks of participating in a multiemployer plan are different from single-employer plans in the following aspects:
•	Assets contributed to the multiemployer plan by one employer may be used to provide benefits to employees of other participating employers.
•	If a participating employer stops contributing to the plan, the unfunded obligations of the plan may be borne by the remaining participating employers.
•	If a participating employer chooses to stop participating in a multiemployer plan, the employer may be required to pay the plan an amount based on the underfunded status of the plan, referred to as a withdrawal liability.
The union-represented employees at Hawesville are part of a United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied Industrial and Service Workers International Union ("USWA") sponsored multiemployer plan.  Our contributions to the plan are determined at a fixed rate per hour worked.
Century’s participation in the plan for the year ended December 31, 2014, is outlined in the table below.
Fund	Steelworkers Pension Trust
EIN / PN	23-6648508/499
Pension Protection Act Zone Status 2014 (1)	Green
Pension Protection Act Zone Status 2013 (1)	Green
Subject to Financial Improvement/Rehabilitation Plan	No
Contributions of Century Aluminum 2014	$2,164
Contributions of Century Aluminum 2013	$2,171
Contributions of Century Aluminum 2012	$2,282
Withdrawal from Plan Probable	No
Surcharge Imposed	No
Expiration Date of Collective Bargaining Agreement	April 1, 2015
-1	The most recent Pension Protection Act zone status available in 2014 and 2013 is for the plan's year-end December 31, 2013 and December 31, 2012, respectively.  The zone status is based on information that Century received from the plan as well as publicly available information per the Department of Labor and is certified by the plan’s actuary. Among other factors, plans in the green zone are at least 80 percent funded.

Share_Based_Compensation

Share Based Compensation	12 Months Ended
	Dec. 31, 2014
Share-based Compensation [Abstract]
Share-based compensation	Share-based compensation
	Amended and Restated Stock Incentive Plan — We award restricted share awards and grant qualified incentive and nonqualified stock options to our salaried officers, non-employee directors, and other key employees from our Amended and Restated Stock Incentive Plan (the "Stock Incentive Plan"). The Stock Incentive Plan has 10,000,000 shares authorized for issuance with approximately 6,900,000 shares remaining at December 31, 2014.  Our share-based compensation consists of service-based (time vested) and performance share awards that typically vest over a period of three years from the date of grant, provided that the recipient is still our employee at the time of vesting. Our independent non-employee directors receive annual grants of service-based share awards that vest following 12 months of service.  In the past, we have granted stock options that have a term of 10 years and typically vest one-third on the grant date and an additional one-third on the first and second anniversary dates of the grant.  Our most recent grant of stock options was in 2009.
	As of December 31, 2014, options to purchase 544,171 shares of common stock and 464,485 service-based share awards were outstanding.
	We also grant annual long-term incentive awards under our Amended and Restated Long-Term Incentive Plan (the "LTIP"). The LTIP is designed to align compensation with the interests of our stockholders by linking compensation to share price appreciation and total stockholder return over a multi-year period. We provide two types of LTIP awards: time-vested performance share units and performance units.
	Time-vested performance share units are stock-settled awards (which do not contain any performance-based vesting requirements) that are granted at the beginning of the performance period.  Performance units are generally cash-settled awards (although the Board of Directors retains the discretion to settle these awards in stock) and vest based on the achievement of pre-determined performance metrics, subject to the discretion of the Board. As of December 31, 2014, we recorded a performance unit liability for approximately $6,251. Both the performance units and time-vested performance share units vest, in their entirety, after three years.
	A summary of activity under our Stock Incentive Plan during the year ended December 31, 2014 is presented below:
	Options	Number		Weighted Average Exercise Price			Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value
	Outstanding at January 1, 2014	619,833		$	24.77
	Exercised	(61,495	)	6.55
	Forfeited/expired	(14,167	)	23.76
	Outstanding, fully vested and exercisable at December 31, 2014 (1)	544,171		$	26.85		2.78	$	3,794
	-1	As the result of actions in 2011 that were determined to be a "change of control" under the Stock Incentive Plan, all options will remain exercisable for their respective remaining term, regardless of whether the awardees remain employees of Century.
	Service-based share awards
	Outstanding at January 1, 2014	442,737
	Granted	258,662
	Vested	(200,965	)
	Forfeited	(35,949	)
	Outstanding at December 31, 2014	464,485
		Year ended December 31,
		2014			2013			2012
	Weighted average per share fair value of service-based share grants	$	15.31		$	8.19		$	8.14
	Total intrinsic value of option exercises	1,011			13			—
	Fair Value Measurement of Share-Based Compensation Awards – We estimate the fair value of each stock option award using the Black-Scholes model on the date of grant.  We have not granted any stock options since 2009. For our service-based awards, the fair value of our service-based awards is equal to the closing stock price on the date of grant. Other assumptions to estimate the fair value have no impact on the fair value of the service-based award. If we grant stock options in future periods, we will disclose the relevant assumptions used in the Black-Scholes model to estimate their fair value.
	The following table summarizes the compensation cost recognized for the years ended December 31, 2014, 2013 and 2012 for all options, service-based share and performance-based share awards.  No share-based compensation cost was capitalized during these periods and there were no significant modifications (other than the accelerated vesting in 2011 described above) of any share-based awards in 2014, 2013 and 2012.
		Year ended December 31,
		2014			2013			2012
	Share-based compensation expense reported:
	Performance-based share expense	$	1,090		$	475		$	27
	Service-based share expense	244			603			586
	Stock option expense	—			—			—
	Total share-based compensation expense before income tax	1,334			1,078			613
	Income tax	—			—			—
	Total share-based compensation expense, net of income tax	$	1,334		$	1,078		$	613
	As of December 31, 2014, we had unrecognized compensation expense of $1,826 before taxes.  This expense will be recognized over a weighted average period of 1.00 years.

Earnings_per_share

Earnings per share	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Earnings (loss) per share	Earnings (loss) per share
	Basic earnings (loss) per share ("EPS") amounts are calculated by dividing net income (loss) allocated to common stockholders by the weighted average number of common shares outstanding.  Diluted EPS amounts assume the issuance of common stock for all potentially dilutive common shares outstanding.
	The following table shows the basic and diluted earnings (loss) per share for 2014, 2013, and 2012:
		For the year ended December 31, 2014
		Net income			Shares (000)		Per-Share
	Net income	$	112,494
	Amount allocated to common stockholders	91.81		%
	Basic EPS:
	Net income allocated to common stockholders	103,283			88,823		$	1.16
	Effect of Dilutive Securities:
	Share-based compensation plans				605
	Diluted EPS:
	Net income allocated to common stockholders with assumed conversion	$	103,283		89,428		$	1.15
		For the year ended December 31, 2013
		Net loss			Shares (000)		Per-Share
	Net loss	$	(40,313	)
	Amount allocated to common stockholders (1)	100		%
	Basic and Diluted EPS:
	Net loss allocated to common stockholders	$	(40,313	)	88,612		$	(0.45	)
		For the year ended December 31, 2012
		Net loss			Shares (000)		Per-Share
	Net loss	$	(35,610	)
	Amount allocated to common stockholders (1)	100		%
	Basic and Diluted EPS:
	Net loss allocated to common stockholders	$	(35,610	)	88,534		$	(0.40	)
	-1	We have not allocated net losses between common and preferred stockholders, as the holders of our preferred shares do not have a contractual obligation to share in the loss.
	Securities excluded from the calculation of diluted EPS:
		2014		2013		2012
	Stock options (1)	320,553		619,833		626,334
	Service-based share awards (1)	—		442,737		396,133
	-1	In periods when we report a net loss, all share awards are excluded from the calculation of diluted weighted average shares outstanding because of their antidilutive effect on earnings (loss) per share.

Income_taxes

Income taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income taxes	Income taxes
	The components of pre-tax book income (loss) consist of the following:
		Year Ended December 31,
		2014			2013			2012
	U.S.	$	77,046		$	(47,080	)	$	(38,762	)
	Foreign	52,451			7,236			9,439
	Total	$	129,497		$	(39,844	)	$	(29,323	)
	Significant components of the income tax expense consist of the following:
		Year Ended December 31,
		2014			2013			2012
	Current:
	U.S. federal current expense (benefit)	$	(112	)	$	532		$	(161	)
	State current expense (benefit)	2,252			(445		)	(669		)
	Foreign current expense	15,098			6,198			9,808
	Total current expense	17,238			6,285			8,978
	Deferred:
	U.S. federal deferred benefit	(1,696		)	(3,905		)	(1,564		)
	State deferred benefit	(12		)	(207		)	—
	Foreign deferred tax expense	2,778			958			1,496
	Total deferred benefit	1,070			(3,154		)	(68		)
	Total income tax expense	$	18,308		$	3,131		$	8,910
	A reconciliation of the statutory U.S. Federal income tax rate to the effective income tax rate on income (loss) is as follows:
		2014		2013		2012
	Federal Statutory Rate	35	%	35	%	35	%
	Permanent differences	4.3		54.5		12.6
	State taxes, net of Federal benefit	(6.3	)	97.2		0.1
	Foreign earnings taxed at different rates than U.S.	(0.5	)	17.4		(369.5	)
	Valuation allowance	(25.4	)	(265.9	)	297.6
	Changes in uncertain tax reserves	0.6		40.5		(6.7	)
	Other	6.4		13.4		0.5
	Effective tax rate	14.1	%	(7.9	)%	(30.4	)%
	The effect of earnings of foreign subsidiaries includes the difference between the U.S. statutory rate and local jurisdiction tax rates, as well as the provision (benefit) for incremental U.S. taxes on unremitted earnings of foreign subsidiaries due to the removal of the election to permanently reinvest the related earnings during 2012.
	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.  Significant components of our deferred tax assets and liabilities as of December 31 are as follows:
		2014			2013
	Deferred tax assets:
	Accrued postretirement benefit cost	$	15,683		$	12,851
	Accrued liabilities	4,494			2,355
	Share-based compensation	7,350			5,327
	Derivative and hedging contracts	58,687			116,550
	Goodwill	10,521			12,421
	Equity contra - other comprehensive loss	81,567			61,216
	Dual consolidated losses and capital losses	7,509			14,512
	Net operating losses and tax credits	646,158			637,721
	Foreign basis differences	668			—
	Other	1,239			1,533
	Total deferred tax assets	833,876			864,486
	Valuation allowance	(748,283		)	(765,023		)
	Net deferred tax assets	$	85,593		$	99,463
	Deferred tax liabilities:
	Tax over financial statement depreciation	$	(142,627	)	$	(145,945	)
	Pension	(14,222		)	(11,543		)
	Unremitted foreign earnings	(30,308		)	(35,344		)
	Foreign basis differences	—			(790		)
	Total deferred tax liabilities	(187,157		)	(193,622		)
	Net deferred tax liability	$	(101,564	)	$	(94,159	)
	Under ASC 740 "Accounting for Income Taxes", a valuation allowance must be established when it is more likely than not that all or a portion of a deferred tax asset will not be realized.  The amount of valuation allowance is based upon our best estimate of our ability to realize the net deferred tax assets.  A valuation allowance can subsequently be reversed when we believe that the assets are realizable on a more likely than not basis.
	The changes in the valuation allowance are as follows:
		2014			2013
	Beginning balance, valuation allowance	$	765,023		$	656,352
	Change in valuation allowance	(16,740		)	108,671
	Ending balance, valuation allowance	$	748,283		$	765,023
	As a result of certain realization requirements of ASC Topic 718 "Compensation - Stock Compensation", the table of deferred tax assets and liabilities shown above does not include net operating loss deferred tax assets at December 31, 2014 and 2013 that arose directly from tax deductions related to equity compensation in excess of compensation recognized for financial reporting. Net operating losses of $7,499 will increase equity if and when such deferred tax assets are ultimately realized.
	The significant components of our NOL carryforwards are as follows:
		2014			2013
Federal (1)	$	1,306,482		$	1,287,118
State (2)	2,078,105			2,077,890
Foreign (3)	446,234			459,457
-1	The federal NOL begins to expire in 2028.
-2	The state NOLs begin to expire in 2027.
-3	The Icelandic NOL begins to expire in 2017; Dutch NOL begins to expire in 2022.
A reconciliation of the beginning and ending amounts of gross unrecognized tax benefits (excluding interest) is as follows:
	2014			2013			2012
Balance as of January 1,	$	1,200		$	17,600		$	15,900
Additions based on tax positions related to the current year	1,100			700			2,700
Decreases due to lapse of applicable statute of limitations	(300		)	(2,800		)	(800		)
Settlements	—			(14,300		)	(200		)
Balance as of December 31,	$	2,000		$	1,200		$	17,600
Included in the above balances are tax positions whose tax characterization is highly certain but for which there is uncertainty about the timing of tax return inclusion.  Because of the impact of deferred tax accounting, other than interest and penalties, the timing would not impact the annual effective tax rate but could accelerate the payment of cash to the taxing authority to an earlier period.  The remaining amounts of unrecognized tax benefits would affect our effective tax rate if recognized.  It is our policy to recognize potential accrued interest and penalties related to unrecognized tax benefits in income tax expense.
The components of our unrecognized tax positions are as follows:
	2014			2013			2012
Highly certain tax positions	$	1,900		$	1,100		$	16,900
Other unrecognized tax benefits	100			100			700
Gross unrecognized tax benefits	$	2,000		$	1,200		$	17,600
Accrued interest and penalties related to unrecognized tax benefits	$	—		$	100		$	100
Century and its subsidiaries file income tax returns in the U.S. federal jurisdiction, various state and local jurisdictions, and several foreign jurisdictions.
In April 2013, we received notice from the Internal Revenue Service ("IRS") that the Congressional Joint Committee on Taxation finalized their review of the US Federal examinations for the income tax years 2008, 2009, and 2010 and refund years of 2004, 2005, 2006, and 2007 without exception to the conclusions reached by the IRS. This Joint Committee is a special nonpartisan Congressional committee involved with the analysis and drafting of federal tax legislation and, as part of its mandate, reviews all federal tax refund claims over a certain amount. As a result of this determination, we have reduced the reserve for the unrecognized tax benefits related to prior years by approximately $14,300. The reduction did not result in an impact to the effective tax rate since the reduction was offset by an increase in our valuation allowance. During the second quarter of 2013, we received refunds from the IRS of $5,009 following the Joint Committee review.
Our federal income tax returns have been reviewed by the IRS through 2010.  However, we have NOL's beginning in 2008 that are available for carryforward to future years.  Under US tax law, NOL's may be adjusted by the IRS until the statute of limitations expires for the year in which the NOL is used.  Accordingly, our 2008 and later NOL's may be reviewed until they are used or expire.  Material state and local income tax matters have been concluded for years through 2007.  The majority of our state returns beginning in 2008 are subject to examination.
As of December 31, 2014, we had federal net operating loss carryforwards of $1,306,482, after adjusting for losses carried back to previous tax years, which could offset future taxable income.  Our ability to utilize our deferred tax assets to offset future federal taxable income may be significantly limited if we experience an "ownership change" as defined in Section 382 of the Internal Revenue Code of 1986, as amended (the "Code"). In general, an ownership change would occur if our "five-percent shareholders," as defined under the Code, collectively increase their ownership in us by more than 50 percentage points over a rolling three-year period.  Future transactions in our stock that may not be in our control may cause us to experience such an ownership change and thus limit our ability to utilize net operating losses, tax credits and other tax assets to offset future taxable income.
Our Icelandic tax returns are subject to examination beginning with the 2009 tax year. A review of our 2010 through 2012 tax years was recently completed by the Directorate of Internal Revenue of Iceland and no further action is expected for this matter.
We do not expect a significant change in the balance of unrecognized tax benefits within the next twelve months.

Commitments_and_contingencies

Commitments and contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments and contingencies	Commitments and contingencies
	Environmental Contingencies
	Based upon all available information, we believe our current environmental liabilities do not have, and are not likely to have, a material adverse effect on our financial condition, results of operations or liquidity. Because of the issues and uncertainties described below and the inability to predict the requirements of future environmental laws, there can be no assurance that future capital expenditures and costs for environmental compliance at currently or formerly owned or operated properties will not result in liabilities that may have a material adverse effect on our financial condition, results of operations or liquidity.
	It is our policy to accrue for costs associated with environmental assessments and remedial efforts when it becomes probable that a liability has been incurred and the costs can be reasonably estimated. The aggregate environmental-related accrued liabilities were $1,101 and $999 at December 31, 2014 and 2013, respectively. All accrued amounts have been recorded without giving effect to any possible future recoveries. With respect to costs for ongoing environmental compliance, including maintenance and monitoring, such costs are expensed as incurred.
	In July 2006, we were named as a defendant, together with certain affiliates of Alcan Inc., in a lawsuit brought by Alcoa Inc. seeking to determine responsibility for certain environmental indemnity obligations related to the sale of a cast aluminum plate manufacturing facility located in Vernon, California, which we purchased from Alcoa Inc. in December 1998, and sold to Alcan Rolled Products-Ravenswood LLC in July 1999. The complaint also seeks costs and attorney fees. The matter is in a preliminary stage in the U.S. District Court for the District of Delaware, and we cannot predict the ultimate outcome of this action or estimate a range of possible losses related to this matter at this time.
	Matters relating to the St. Croix Alumina Refining Facility
	We are a party to a United States Environmental Protection Agency Administrative Order on Consent (the "Order") pursuant to which certain past and present owners of an alumina refining facility at St. Croix, Virgin Islands (the "St. Croix Alumina Refinery") have agreed to carry out a Hydrocarbon Recovery Plan to remove and manage hydrocarbons floating on groundwater underlying the facility.  Pursuant to the Hydrocarbon Recovery Plan, recovered hydrocarbons and groundwater are delivered to the adjacent petroleum refinery where they are received and managed. In connection with the sale of the facility by Lockheed Martin Corporation ("Lockheed") to one of our affiliates, Virgin Islands Alumina Corporation ("Vialco"), in 1989, Lockheed, Vialco and Century entered into the Lockheed-Vialco Asset Purchase Agreement. The indemnity provisions contained in the Lockheed-Vialco Asset Purchase Agreement allocate responsibility for certain environmental matters. Lockheed has tendered indemnity to Vialco. We have likewise tendered indemnity to Lockheed. Through December 31, 2014, we have expended approximately $1,033 on the Hydrocarbon Recovery Plan.  At this time, we are not able to estimate the amount of any future potential payments under this indemnification to comply with the Order, but we do not anticipate that any such amounts will have a material adverse effect on our financial condition, results of operations or liquidity, regardless of the final outcome. Vialco sold the St. Croix Alumina Refinery to St. Croix Alumina, LLC, a subsidiary of Alcoa in 1995.
	In December 2010, Century was among several defendants named in a lawsuit filed by plaintiffs who either worked, resided or owned property in the area downwind from the St. Croix Alumina Refinery. In March 2011, Century was also named a defendant in a nearly identical suit brought by certain additional plaintiffs. The plaintiffs in both suits allege damages caused by the presence of red mud and other particulates coming from the alumina facility and are seeking unspecified monetary damages, costs and attorney fees as well as certain injunctive relief. We have tendered indemnity and defense to St. Croix Alumina LLC and Alcoa Alumina & Chemical LLC under the terms of an acquisition agreement relating to the facility and have filed motions to dismiss plaintiffs’ claims, but the Superior Court of the Virgin Islands, Division of St. Croix has not yet ruled on the motions. At this time, it is not practicable to predict the ultimate outcome of or to estimate a range of possible losses for any of the foregoing actions relating to the St. Croix Alumina Refinery.
	Legal Contingencies
	In addition to the foregoing matters, we have pending against us or may be subject to various lawsuits, claims and proceedings related primarily to employment, commercial, stockholder, safety and health matters.
	In evaluating whether to accrue for losses associated with legal contingencies, it is our policy to take into consideration factors such as the facts and circumstances asserted, our historical experience with contingencies of a similar nature, the likelihood of our prevailing and the severity of any potential loss.  For some matters, no accrual is established because we have assessed our risk of loss to be remote.  Where the risk of loss is probable and the amount of the loss can be reasonably estimated, we record an accrual, either on an individual basis or with respect to a group of matters involving similar claims, based on the factors set forth above.
	When we have assessed that a loss associated with legal contingencies is reasonably possible, we determine if estimates of possible losses or ranges of possible losses are in excess of related accrued liabilities, if any. Based on current knowledge, management has ascertained estimates for losses that are reasonably possible and management does not believe that any reasonably possible outcomes in excess of our accruals, if any, either individually or in aggregate, would be material to our financial condition, results of operations, or liquidity. We reevaluate and update our assessments and accruals as matters progress over time.
	In June 2014, we reached a settlement with OR pursuant to the terms of which, among other things, Nordural Grundartangi ehf agreed to pay $3,600 to OR and OR withdrew and released each of Nordural Grundartangi ehf and Nordural Helguvik ehf from and against all claims related to the reduction in the power purchased under the existing power contracts. This settlement amount was paid in July 2014. As part of the settlement, Nordural Helguvik ehf and OR also entered into a Supplemental Power Contract pursuant to which OR agreed to provide supplemental power to Grundartangi or Helguvik from time to time during the remaining term of the existing Nordural Helguvik ehf power contract with OR.
	Ravenswood Retiree Medical Benefits changes
	In November 2009, CAWV filed a class action complaint for declaratory judgment against the USWA, the USWA’s local and certain CAWV retirees, individually and as class representatives, seeking a declaration of CAWV’s rights to modify/terminate retiree medical benefits.  Later in November 2009, the USWA and representatives of a retiree class filed a separate suit against CAWV, Century Aluminum Company, Century Aluminum Master Welfare Benefit Plan, and various John Does with respect to the foregoing.  These actions, entitled Dewhurst, et al. v. Century Aluminum Co., et al., and Century Aluminum of West Virginia, Inc. v. United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied Industrial and Service Workers International Union, AFL-CIO/CLC, et al., have been consolidated and venue has been set in the District Court for the Southern District of West Virginia.
	In January 2010, the USWA filed a motion for preliminary injunction to prevent us from implementing any modifications to the retiree medical benefits while these lawsuits are pending, which was dismissed by the trial court, and affirmed upon appeal. CAWV has filed a motion for summary judgment of these actions. The case in chief is currently proceeding in the trial court, subject to the court’s ruling on the motion for summary judgment.
	PBGC Settlement
	In June 2011, the PBGC informed us that it believed a "cessation of operations" under ERISA had occurred at our Ravenswood facility as a result of the curtailment of operations at the facility. Although we disagree that a "cessation of operations" occurred, we entered into a settlement agreement with the PBGC in April 2013 to resolve the matter. Pursuant to the terms of the agreement, we will make additional contributions (above any minimum required contributions) to our defined benefit pension plans totaling approximately $17,400 over the term of the agreement. During 2013, we made contributions pursuant to this agreement of approximately $6,700. Under certain circumstances, in periods of lower primary aluminum prices relative to our cost of operations, we may defer one or more of these payments, but we would be required to provide the PBGC with acceptable security for any deferred payments. In the first quarter of 2014, we elected to defer contributions for 2014 under the PBGC agreement and have provided the PBGC with the appropriate security.
	Power Commitments and Contingencies
	Hawesville
	Effective August 2013, we entered into a power supply arrangement with Kenergy and Big Rivers which provides market-based power to the Hawesville smelter. The power supply arrangement has an effective term through December 2023. Under this arrangement, the power companies purchase power on the open market and pass it through to Hawesville at Midcontinent Independent System Operator ("MISO") pricing plus transmission and other costs incurred by Kenergy. In connection with this power arrangement, CAKY has received approval from applicable regional transmission organizations and regulatory bodies regarding grid stability and energy import capability. Effective January 1, 2015, new agreements were approved by the Kentucky Public Service Commission pursuant to which EDF Trading North America, LLC ("EDF") replaced Big Rivers as our market participant with MISO under this arrangement.
	Sebree
	Effective February 2014, we entered into a power supply arrangement with Kenergy and Big Rivers which provides market based power to the Sebree smelter. The power supply arrangement has an effective term through December 2023. Similar to the arrangement at Hawesville, the power companies purchase power on the open market and pass it through to Sebree at MISO pricing plus transmission and other costs incurred by Kenergy.  Effective January 1, 2015, new agreements were approved by the Kentucky Public Service Commission pursuant to which EDF replaced Big Rivers as our market participant with MISO under this arrangement.
	Mt. Holly
	Mt. Holly has a power purchase agreement (the "Santee Cooper Agreement") with the South Carolina Public Service Authority ("Santee Cooper") with an effective term through December 2015.  The Santee Cooper Agreement provides power for Mt. Holly’s full production capacity requirements at prices based on published rate schedules (which are subject to change), with adjustments for fuel prices and other items.  The Santee Cooper Agreement restricts Mt. Holly’s ability to reduce its power consumption (or the associated payment obligations) below contracted levels and to terminate the agreement, unless, in each case, the LME falls below certain negotiated levels.
	On June 30, 2014, Mt. Holly gave notice to Santee Cooper under the Santee Cooper Agreement to reduce the contract demand to zero effective December 31, 2015. We are continuing discussions with Santee Cooper and other parties regarding power arrangements for Mt. Holly following December 31, 2015.
	Ravenswood
	CAWV has a power purchase agreement (the "APCo Agreement") with the Appalachian Power Company ("APCo").  CAWV currently purchases a limited amount of power from APCo as necessary to maintain its curtailed smelter.  Power is supplied under the APCo Agreement at prices set forth in published tariffs (which are subject to change), with certain adjustments.
	Grundartangi
	Nordural Grundartangi ehf has power purchase agreements with HS Orka hf ("HS"), Landsvirkjun and Orkuveita Reykjavikur ("OR") to provide power to its Grundartangi smelter.  These power purchase agreements, which will expire on various dates from 2019 through 2036 (subject to extension), provide power at LME-based variable rates.  Each power purchase agreement contains take-or-pay obligations with respect to a significant percentage of the total committed and available power under such agreement.
	In the fourth quarter of 2011, an additional 47.5 MW of power became available under a power purchase agreement with OR. This power can be used at either Grundartangi or Helguvik and a portion is currently being utilized at Grundartangi.
	In June 2012, Nordural Grundartangi ehf entered into a supplemental power contract with Landsvirkjun. The supplemental power contract, which will expire in October 2029 (or upon the occurrence of certain earlier events), will provide Nordural Grundartangi ehf with supplemental power, as Nordural Grundartangi ehf may request from time to time, at LME-based variable rates. Nordural Grundartangi ehf has agreed to make certain prepayments to Landsvirkjun for power expected to be used at a later date in connection with the contract, which will reduce the price paid for power at the time of consumption. As of December 31, 2014, these power prepayments totaled approximately $2,062.
	Helguvik
	Nordural Helguvik ehf has power purchase agreements with HS and OR to provide power to the Helguvik project.  These power purchase agreements provide power at LME-based variable rates and contain take-or-pay obligations with respect to a significant percentage of the total committed and available power under such agreements.  The power purchase agreements with HS and OR to provide power to Helguvik contain certain conditions to HS’s and OR’s obligations. HS (with respect to all phases) and OR (with respect to all phases other than the first phase) have alleged that certain of these conditions have not been satisfied. The first stage of power under the OR power purchase agreement (approximately 47.5 MW) became available in the fourth quarter of 2011 and is currently being utilized at Grundartangi.  In July 2014, HS commenced arbitration proceedings against Nordural Helguvik ehf seeking, among other things, an order declaring, (i) that the conditions to the power contract have not been fulfilled and, (ii) that the power contract is therefore no longer valid. Nordural Helguvik ehf believes HS' renewed claims are without merit and intends to defend itself against them. Nordural Helguvik ehf is in discussions with both HS and OR with respect to such conditions and other matters pertaining to these agreements.
	In June 2014, Nordural Helguvik ehf entered into a supplemental power contract with OR. The supplemental power contract will expire in October 2036 (or upon the occurrence of certain earlier events) and will provide Grundartangi or Helguvik with supplemental power at LME-based rates, as may be requested from Grundartangi or Helguvik from time to time.
	Other Commitments and Contingencies
	Labor Commitments
	The bargaining unit employees at our Grundartangi, Vlissingen, Hawesville, Sebree and Ravenswood facilities are represented by labor unions, representing 59% of our total workforce.
	81% of Grundartangi’s work force is represented by five labor unions, governed by a labor agreement that establishes wages and work rules for covered employees. This agreement expired on December 31, 2014. Since such time, we have been operating under the terms of the expired agreement while we engage in negotiations with the unions regarding the terms of a new agreement. 80% of Vlissingen's work force is represented by the FME, governed by a labor agreement that expires on May 1, 2015. The FME negotiates working conditions with trade unions on behalf of its members.
	54% of our U.S. based work force is represented by USWA. CAKY’s Hawesville employees represented by the USWA are under a collective bargaining agreement that expires on March 31, 2015. CAKY is currently in negotiations with the USWA for a new agreement. In July 2014, Century Sebree entered into a new collective bargaining agreement with the USWA for its employees at the Sebree smelter.  The agreement is effective through October 28, 2019. The labor agreement for CAWV’s Ravenswood plant employees represented by the USWA expired on August 31, 2010.

Forward_delivery_contracts_and

Forward delivery contracts and financial instruments	12 Months Ended
	Dec. 31, 2014
Forward Delivery Contracts and Financial Instruments [Abstract]
Forward delivery contracts and financial instruments	Forward delivery contracts and financial instruments
	As a producer of primary aluminum, we are exposed to fluctuating raw material and primary aluminum prices.  From time to time we enter into fixed and market priced contracts for the sale of primary aluminum and the purchase of raw materials in future periods.
	Forward Physical Delivery Agreements
	Primary Aluminum Sales Contracts
	Contract	Customer	Volume	Term	Pricing
	Glencore Grundartangi Metal Agreement (1)	Glencore	All primary aluminum produced at Grundartangi, net of tolling and other sales commitments	January 1, 2014 through December 31, 2017	Variable, based on LME and European Duty Paid premium and product premiums, as applicable
	-1	The Glencore Grundartangi Metal Agreement is for all metal produced at Grundartangi from 2014 through 2017 less commitments under existing tolling and other sales contracts.  Grundartangi currently estimates that it will sell Glencore approximately 205,000 tonnes of aluminum under this agreement in 2015.
	See Note 22 Subsequent events for additional information about a new aluminum supply agreement with Glencore.
	Tolling Contracts
	Contract	Customer	Volume	Term	Pricing
	Glencore Toll Agreement	Glencore	90,000 tonnes per year ("tpy")	Through July 2016	Variable, based on LME and European Duty Paid premium
	Apart from the Glencore Grundartangi Metal Agreement, the Southwire Metal Agreement (which expired at the end of 2014) and the Glencore Sweep Agreement (a contract for all metal produced in the U.S. in 2013, less existing sales agreements and valued-added metal sales, which expired at the end of 2013), we had the following forward delivery contractual commitments:
	Other forward delivery contracts
		December 31, 2014		December 31, 2013
		(in tonnes)
	Other forward delivery contracts – total	6,108		118,373
	Other forward delivery contracts – Glencore	4,058		20,008
	We had no outstanding primary aluminum forward financial sales contracts at December 31, 2014. We had no fixed price forward financial contracts to purchase aluminum at December 31, 2014.

Asset_retirement_obligations_A

Asset retirement obligations (“ARO”)	12 Months Ended
	Dec. 31, 2014
Asset Retirement Obligation Disclosure [Abstract]
Asset retirement obligations (“ARO”)	Asset retirement obligations ("ARO")
	Our asset retirement obligations consist primarily of costs associated with the disposal of spent pot liner used in the reduction cells of our domestic facilities.
	The reconciliation of the changes in the asset retirement obligations is presented below:
		Year ended December 31,
		2014			2013
	Beginning balance, ARO liability	$	27,113		$	16,124
	Additional ARO liability incurred	2,548			1,730
	ARO liabilities settled	(4,731		)	(2,580		)
	Accretion expense	1,517			1,733
	Additional ARO liability from Sebree acquisition	—			10,106
	Additional ARO liability from Mt. Holly acquisition	10,503			—
	Ending balance, ARO liability	$	36,950		$	27,113
	Certain conditional AROs related to the disposal costs of fixed assets at our primary aluminum facilities have not been recorded because they have an indeterminate settlement date.  These conditional AROs will be initially recognized in the period in which sufficient information exists to estimate their fair value.

Supplemental_cash_flow_informa

Supplemental cash flow information	12 Months Ended
	Dec. 31, 2014
Supplemental Cash Flow Information [Abstract]
Supplemental cash flow information	Supplemental cash flow information
		Year Ended December 31,
		2014		2013		2012
	Cash paid for:
	Interest	$	19,066	$	20,539	$	20,212
	Income/withholding taxes (1)	12,189		28,654		41,455
	Non-cash investing activities:
	Accrued capital costs	$	744	$	9,409	$	(683	)
	-1	We paid withholding taxes in Iceland on intercompany dividends of $5,491, $18,067 and $22,633 during the years ended December 31, 2014, 2013 and 2011, respectively. Our tax payments in Iceland for withholding taxes, income taxes and any associated refunds are denominated in ISK.

Quarterly_Information_Unaudite

Quarterly Information (Unaudited)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Data [Abstract]
Quarterly information (unaudited)	Quarterly information (Unaudited)
	Financial results by quarter for the years ended December 31, 2014 and 2013 are as follows:
		Net sales		Gross profit (loss)			Net income (loss)			Net income (loss) allocated to common stockholders			Basic			Diluted earnings (loss) per share
													earnings (loss) per share
	2014
	4th Quarter (1)	$	551,239	$	89,996		$	61,849		$	56,824		$	0.64		$	0.63
	3rd Quarter (2)	500,632		75,714			50,405			46,277			0.52			0.52
	2nd Quarter (3)	458,324		38,504			20,344			18,675			0.21			0.21
	1st Quarter (4)	420,847		(1,758		)	(20,104		)	(20,104		)	(0.23		)	(0.23		)
	2013
	4th Quarter (5)	$	401,174	$	15,285		$	(9,675	)	$	(9,675	)	$	(0.11	)	$	(0.11	)
	3rd Quarter (6)	399,928		12,354			(9,507		)	(9,507		)	(0.11		)	(0.11		)
	2nd Quarter (7)	331,937		(5,698		)	(29,384		)	(29,384		)	(0.33		)	(0.33		)
	1st Quarter (8)	321,274		17,582			8,253			7,567			0.09			0.09
	-1	The fourth quarter of 2014 net income included a benefit of $7,943 for the gain on remeasurement of contingent consideration and a benefit of $1,318 for gain on remeasurement of our equity investment in Mt. Holly. Results were negatively impacted by $4,964 in non-cash, non-recurring pension charges and by $2,616 related to the separation of former senior executives.
	-2	The third quarter of 2014 net income reflects higher aluminum prices and lower power prices in the Midwestern U.S.
	-3	The second quarter of 2014 net income reflects higher aluminum prices and lower power prices in the Midwestern U.S. Results were negatively impacted by a charge of $500 for the finalization of a legal settlement.
	-4	The first quarter of 2014 cost of sales included a benefit of $5,534 related to deferred power contract liability amortization. Results were negatively impacted by a $3,100 charge for increased legal reserves.
	-5	The fourth quarter of 2013 cost of sales included a benefit of $16,570 related to deferred power contract liability amortization. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a credit of $9,040. The financial results also include an $8,400 charge relating to the separation of our former CEO.
	-6	The third quarter of 2013 cost of sales included an $11,720 benefit for deferred power contract liability amortization. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a credit of $5,762.
	-7	The second quarter of 2013 amounts differ from our reported second quarter results due to purchase price accounting adjustments related to the Sebree acquisition which were retroactively applied to the second quarter of 2013. The second quarter of 2013 net loss included a gain on bargain purchase of $5,253 and power contract amortization of $2,741 associated with the Sebree acquisition. Results were negatively impacted by a charge of $3,272 for the early extinguishment of our 8.0% Notes and a charge for severance and other expenses of $1,750 related to our corporate headquarters relocation. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a charge of $10,211.
	-8	The first quarter of 2013 net income included a net benefit of $2,225 related to a litigation reserve adjustment and an unrealized gain of $15,722 related to a LME-based contingent obligation. Results were negatively impacted by severance and other expenses of $2,213 related to our corporate headquarters relocation. The net effect of reporting inventory on a lower of cost or market basis was a charge to cost of goods sold of $5,838 in the quarter.

Business_Segments

Business Segments	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Business segments	Business segments
	Century Aluminum is a producer of primary aluminum, which trades as a global commodity. We are organized as a holding company with each of our operating primary aluminum smelters managed and operated as a separate facility reporting to our corporate headquarters. Each of our operating primary aluminum smelters meets the definition of an operating segment based on factors delineated in ASC 280 "Segment Reporting." We evaluated the similar economic and other characteristics, including nearly identical products, production processes, customers and distribution and have aggregated our four operating segments into one reportable segment, primary aluminum, based on these factors. In addition, all of our primary aluminum smelters share several key economic factors inherent in their common products and production processes. For example, all of our facilities' revenue is based on the LME price for primary aluminum.
	A reconciliation of our consolidated assets to the total of primary aluminum segment assets is provided below.
	Segment assets (1)	2014		2013		2012
	Primary	$	1,971,900	$	1,770,749	$	1,730,321
	Corporate, unallocated	42,135		39,447		46,005
	Total assets	$	2,014,035	$	1,810,196	$	1,776,326
	-1	Segment assets include accounts receivable, due from affiliates, prepaid and other current assets, inventory, intangible assets and property, plant and equipment — net; the remaining assets are unallocated corporate assets.
	Geographic information
	Included in the consolidated financial statements are the following amounts related to geographic locations:
		2014		2013		2012
	Net sales:
	United States	$	1,370,570	$	1,022,081	$	821,976
	Iceland	560,472		432,232		450,135
	Long-lived assets: (1)
	United States	$	487,536	$	392,424	$	368,897
	Iceland	831,507		853,636		869,809
	Other	95,752		93,075		50,223
	-1	Includes long-lived assets other than financial instruments.
	Major customer information
	The following table shows our major customers whose sales revenue exceeded 10% of our net sales.  A loss of any of these customers could have a material adverse effect on our results of operations.  The net sales revenue for these customers is as follows:
		Year Ended December 31,
		2014		2013		2012
	Glencore	$	1,262,101	$	511,051	$	552,299
	Southwire	226,740		312,102		346,311
	RTA	—		223,353		—
	BHP Billiton	—		191,445		202,500

Related_Party_Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2014
Related Party Transactions [Abstract]
Related party transactions	Related party transactions
	The significant related party transactions occurring during the years ended December 31, 2014, 2013 and 2012 are described below.
	Sales to Glencore
	We sold primary aluminum under spot and long-term sales contracts with Glencore at prices based on the LME price for primary aluminum, as adjusted to reflect the Midwest premium (a premium typically added for deliveries of aluminum within the U.S.) and product premiums. In addition, we received tolling fees from Glencore under tolling agreements that provide for delivery of primary aluminum produced at Grundartangi. The fee paid by Glencore under these tolling agreements is based on the LME price for primary aluminum, as adjusted to reflect the exemption from the European Duty Paid premium for Icelandic primary aluminum. We believe that all of the transactions with Glencore were at prices that approximate market. See Note 16 Forward contracts and financial instruments for additional information about our forward physical delivery contracts and tolling agreements with Glencore.
	We had a long-term contract to sell Glencore primary aluminum, at a variable price based on the LME, adjusted by a negotiated U.S. Midwest market premium with a cap and floor as applied to the current U.S. Midwest premium, which expired at the end of 2013.  In addition, we had a contract to sell Glencore all U.S. produced primary aluminum, less existing sales agreements and high-purity metal sales, which expired at the end of 2013. We sold high-purity metal in 2013 on a spot basis at variable prices based on the LME, plus U.S. Midwest premium and product premiums.
	See Note 22 Subsequent events for additional information about a new aluminum supply agreement with Glencore.
	Purchases from Glencore
	We purchase alumina from Glencore on both a spot and long-term contract basis. We believe that all of the alumina purchased under these long-term contracts was purchased at prices which approximated market. For alumina purchased from Glencore on a spot basis, we determined the market price for the spot alumina we purchased based on a survey of suppliers at the time that had the ability to deliver spot alumina on the specified terms.  Based on this survey, we believe that all of the alumina purchased on a spot basis from Glencore was purchased at prices that approximate market.
	Alumina contract and amendments.  We are party to a long-term alumina supply agreement with Glencore, in which Glencore has agreed to supply us with alumina through 2017 at prices indexed to the LME price of primary aluminum. In 2014, upon mutual agreement, approximately half of the purchases under this agreement was priced based on a published alumina index. For 2015, we have agreed to price all of the purchases under this agreement based on a published alumina index. We had additional agreements to buy alumina from Glencore, which expired at the end of 2014 and 2013.  In 2014, 2013 and 2012, the pricing on these alumina purchase agreements for Grundartangi was indexed to the LME price for primary aluminum. We believe that the alumina purchased from Glencore under these contracts was purchased at prices that approximate market.
	Primary aluminum put options
	During 2011, we entered into primary aluminum put option contracts with Glencore that settled in 2012.  We paid cash premiums to enter into these contracts.  We believe that the cash premiums paid to Glencore under these contracts were purchased at prices that approximate market.
	Transactions with BHH
	We own a 40% stake in BHH, a carbon anode and cathode facility located in the Guangxi Zhuang Autonomous Region of south China.  We have a long-term agreement with BHH to provide carbon anodes to Grundartangi through December 31, 2015.  We believe that the carbon anodes purchased from BHH were purchased at prices that approximate market.
	Summary
	A summary of the aforementioned related party transactions for the years ended December 31, 2014, 2013 and 2012 is as follows:
		Year Ended December 31,
		2014		2013		2012
	Net sales to Glencore	$	1,262,101	$	511,051	$	552,299
	Purchases from Glencore	285,167		173,693		145,589
	Purchases from BHH	47,804		86,678		39,337

Subsequent_events

Subsequent events	12 Months Ended
	Dec. 31, 2014
Subsequent Events [Abstract]
Subsequent events	Subsequent Events
	We have evaluated all subsequent events through the date the financial statements were issued.
	Aluminum Purchase Agreement
	We have entered into a new aluminum supply agreement with Glencore pursuant to which we have agreed to sell, and Glencore has agreed to purchase, substantially all of our primary aluminum production in North America for 2015 and 2016 at variable prices determined by reference to the Midwest Transaction Price plus additional product premiums.
	Century Aluminum Expands Share Repurchase Program
	On February 26, 2015, we announced that our Board of Directors has increased the size of our ongoing share repurchase program by $20,000. In 2015 through February 27, 2015, we repurchased $5,840 of our common stock. Together with this increase and the 2015 repurchases, we had a total of $24,276 authorized for future share repurchases. See Note 7 Shareholders' equity for additional information about the stock repurchase program.

Schedule_II_Valuation_and_Qual

Schedule II - Valuation and Qualifying Accounts (Notes)	12 Months Ended
	Dec. 31, 2014
Valuation and Qualifying Accounts [Abstract]
Schedule of Valuation and Qualifying Accounts Disclosure	SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS
		Balance at Beginning of Period		Charged To Cost and Expense		Charged to other accounts			Deductions		Balance at End of Period
		(Dollars in thousands)
	Year ended December 31, 2012
	Allowance for doubtful trade accounts receivable	$	734	$	—	$	—		$	—	$	734
	Deferred tax asset - valuation allowance	$	773,714	$	—	$	(117,362	)	$	—	$	656,352
	Year ended December 31, 2013
	Allowance for doubtful trade accounts receivable	$	734	$	—	$	—		$	—	$	734
	Deferred tax asset - valuation allowance	$	656,352	$	—	$	108,671		$	—	$	765,023
	Year ended December 31, 2014
	Allowance for doubtful trade accounts receivable	$	734	$	—	$	266		$	—	$	1,000
	Deferred tax asset - valuation allowance	$	765,023	$	—	$	(16,740	)	$	—	$	748,283

Recovered_Sheet1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation — The consolidated financial statements include the accounts of Century Aluminum Company and our subsidiaries, after elimination of all intercompany transactions and accounts. Our interest in the BHH joint venture are accounted for under the equity method. For BHH, we report our investment in its results of operations on a one-quarter lag.
Reclassification	Reclassification — Certain immaterial amounts reported in previous years have been reclassified to conform to the current period presentation.
Revenue recognition	Revenue recognition — Revenue is recognized when title and risk of loss pass to customers in accordance with contract terms.  In some instances, we invoice our customers prior to physical shipment of goods.  In such instances, revenue is recognized only when the customer has specifically requested such treatment and has made a commitment to purchase the product.  The goods must be complete, ready for shipment and physically separated from other inventory with risk of ownership passing to the customer.  We must retain no performance obligations
Cash and Cash Equivalents	Cash and Cash Equivalents — Cash and cash equivalents are comprised of cash, money market funds and short-term investments having original maturities of three months or less. The carrying amount of cash equivalents approximates fair value.
Accounts Receivable	Accounts Receivable — The accounts receivable are net of an allowance for uncollectible accounts of $1,000 and $734 at December 31, 2014 and 2013, respectively.
Inventories	Inventories — Our inventories are stated at the lower of cost or market ("LCM"), using the first-in, first-out ("FIFO") method.
Property, Plant and Equipment	Property, Plant and Equipment — Property, plant and equipment is stated at cost.  Additions, renewals and improvements are capitalized.  Asset and accumulated depreciation accounts are relieved for dispositions with resulting gains or losses included in other income – net.  Maintenance and repairs are expensed as incurred.  We capitalize interest for the construction of qualifying assets.  Depreciation of plant and equipment is provided for by the straight-line method over the following estimated useful lives:
	Building and improvements    10 to 45 years
	Machinery and equipment         5 to 35 years
Impairment of long-lived assets	Impairment of long-lived assets — We review our property, plant and equipment for potential impairment whenever events or circumstances indicate that the carrying amount of these assets (asset group) may not be recoverable.  The carrying amount of the assets (asset group) is not recoverable if it exceeds the sum of the undiscounted cash flows expected to result from the use and eventual disposition of the assets (asset group). In that case, an impairment loss would be recognized for the amount in which the carrying amount exceeds the fair value of the assets (asset group), with the fair value determined using the anticipated cash flows discounted at a rate commensurate with the risk involved. We estimate the future cash flows using management’s assumptions about the expected future use of the assets (asset group), the remaining useful life, expenditures to maintain the service potential, market and other cost assumptions.
	Determination as to whether and how much an asset is impaired involves significant management judgment involving highly uncertain matters, including estimating the future sales volumes, future selling prices and cost, alternative uses for the asset, and estimated proceeds from the disposal of the asset.  However, the impairment reviews and calculations are based on estimates and assumptions that take into account our business plans and long-term investment decisions at the time of such impairment reviews. We did not recognize any impairment losses on our long-lived fixed assets during 2014, 2013 or 2012.
Business Acquisitions	Business Acquisitions — We account for business acquisitions by applying the acquisition method in accordance with Financial Accounting Standards Board ("FASB") Accounting Standards Codification ("ASC") 805 "Business Combinations." We allocate the purchase price to the assets acquired and liabilities assumed based on their estimated fair values on the date of the acquisition. The difference between the fair value of the net assets acquired and the purchase price is recorded as either goodwill or a bargain purchase gain. We record the operating results of our acquired businesses in our consolidated statements of operations from the date of acquisition.
Other Assets	Other Assets — Other assets consist primarily of Century’s investments in joint ventures, deferred financing costs, assets held in a Rabbi trust to fund the non-qualified supplemental executive retirement benefits ("SERB") pension benefit obligation, prepaid power costs, internal use software and operating maintenance supplies not expected to be consumed within the year. Our equity share of the undistributed earnings (loss) increases (decreases) the investment in the joint ventures.  Deferred financing costs are amortized on a straight-line basis over the life of the related financial instrument.
	Prior to the Acquisition, we accounted for our interest in the Mt. Holly partnership using the equity method of accounting.  Additionally, our undivided interest in certain property, plant and equipment of Mt. Holly was held outside of the partnership and the undivided interest in these assets of the facility was accounted for in accordance with the ASC 810-10-45-14 "Investor Balance Sheet and Income Statement Display under the Equity Method for Investments in Certain Partnerships and Other Ventures."  Accordingly, prior to the Acquisition, the undivided interest in these assets and the related depreciation were accounted for on a proportionate gross basis.
Income Taxes	Income Taxes — We account for income taxes using the asset and liability method, whereby deferred income taxes reflect the net tax effect of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes.  In evaluating our ability to realize deferred tax assets, we use judgment in considering the relative impact of negative and positive evidence. The weight given to the potential effect of negative and positive evidence is commensurate with the extent to which it can be objectively verified.  Based on the weight of evidence, both negative and positive, if it is more likely than not that some portion or all of a deferred tax asset will not be realized, a valuation allowance is established.  Accordingly, we have a valuation allowance against all of our net federal and state deferred tax assets.  We have a valuation allowance against a portion of our Icelandic and all of our Hong Kong and the Netherlands net operating loss ("NOL") deferred tax assets due to our belief that it is more likely than not that these assets will not be realized.  During 2012, we removed our election to permanently reinvest foreign earnings. See Note 14 Income taxes for additional information.
Defined Benefit Pension and Other Postretirement Benefits]	Defined Benefit Pension and Other Postretirement Benefits — We sponsor defined benefit pension and other postretirement benefit ("OPEB") plans for certain of our domestic hourly and salaried employees. We recognize expenses, assets and liabilities based on actuarial assumptions. We contribute to our defined benefit pension plans based upon actuarial and economic assumptions designed to achieve adequate funding of the projected benefit obligations and to meet the minimum funding requirements.  In addition, we maintain the SERB plan for certain current and former executive officers.  We account for these plans in accordance with ASC 715 "Compensation — Retirement Benefits." We use a measurement date of December 31st to determine the pension and OPEB liabilities.
Postemployment Benefits
	Postemployment Benefits — We provide certain postemployment benefits to certain former and inactive employees and their dependents during the period following employment, but before retirement. These benefits include salary continuance, supplemental unemployment and disability healthcare.  We recognize the estimated future cost of providing postemployment benefits on an accrual basis over the active service life of the employee.
Derivatives and hedging	Derivatives and hedging — We enter into fixed and market priced contracts for the sale of primary aluminum and the purchase of raw materials in future periods.  We also enter into fixed price financial sales contracts and put option contracts to manage our exposure to changing primary aluminum prices.
	Certain physical delivery and financial sales contracts for primary aluminum that are not designated cash flow hedges or do not qualify for cash flow hedge treatment are marked-to-market quarterly.  Fluctuations in the London Metal Exchange ("LME") price of primary aluminum may have a significant impact on gains and losses included in our financial statements from period to period.  We recognize the unrealized and realized gains and losses associated with these contracts in net gain (loss) on forward and derivative contracts.
	See Note 4 Fair value measurements and Note 5 Derivatives and hedging instruments for additional information about these contracts.
Foreign Currency	Foreign Currency – We are exposed to foreign currency risk due to fluctuations in the value of the U.S. dollar as compared to the euro, the Icelandic krona ("ISK") and the Chinese yuan.  Grundartangi and Vlissingen use the U.S. dollar as their functional currency, however a portion of the operating expenses of their respective facilities are denominated and payable in currencies other than the U.S. dollar.  Grundartangi’s labor costs, part of its maintenance costs and other local services are denominated in ISK and a portion of its anode costs are denominated in euros.  Labor costs, maintenance costs and other local services at Vlissingen are denominated in euros. Transactions denominated in currencies other than the functional currency are recorded based on exchange rates at the time such transactions arise and any transaction gains and losses are reflected in other income – net in the consolidated statements of operations. As a result, an increase or decrease in the value of those currencies relative to the U.S. dollar would affect Grundartangi’s and Vlissingen's operating margins.  In addition, our joint venture investment in BHH uses the Chinese yuan as its functional currency.  For our joint venture investments, we record gains and losses associated with foreign currency exchange rates in equity in earnings of joint ventures.
Financial Instruments	Financial Instruments — Our receivables, certain life insurance policies, payables, borrowings under our revolving credit facilities and debt related to industrial revenue bonds ("IRBs") are carried at amounts that approximate fair value.  The following table provides the carrying amounts and approximate fair values (based on the last available trading data) of our 7.5% senior secured notes due 2021 (the "7.5% Notes due 2021") and our 7.5% senior unsecured notes due 2014 (the "7.5% Notes due 2014"). See Note 4 Fair value measurements for additional information about these financial instruments.
		December 31, 2014				December 31, 2013
		Carrying amount		Fair value		Carrying amount		Fair value
	7.5% Notes due 2021	$	246,888	$	256,408	$	246,528	$	244,375
	7.5% Notes due 2014	—		—		2,603		2,487
Earnings per share	Earnings per share — Basic earnings (loss) per share ("EPS") amounts are calculated by dividing earnings (loss) available to common stockholders by the weighted average number of common shares outstanding.  Diluted EPS amounts assume the issuance of common stock for all potentially dilutive common shares outstanding.
	Our Series A Convertible Preferred Stock has similar characteristics to a "participating security" as described by ASC 260 "Earnings per Share" and we calculate the amount of net income (loss) allocated to common stockholders and basic EPS using the Two-Class Method earnings allocation formula, allocating undistributed income to our preferred shareholder consistent with their participation rights, and diluted EPS using the If-Converted Method when applicable.
	Our Series A Convertible Preferred Stock is a non-cumulative perpetual participating convertible preferred stock with no set dividend preferences.  The holders of our convertible preferred stock do not have a contractual obligation to share in our losses.  In periods where we report net losses, we do not allocate these losses to the convertible preferred stock for the computation of basic or diluted EPS.
Asset Retirement Obligations	Asset Retirement Obligations — We are subject to environmental regulations which create certain legal obligations related to the normal operations of our domestic primary aluminum smelter operations. Our asset retirement obligations ("AROs") consist primarily of costs associated with the disposal of spent pot liner used in the reduction cells of our domestic facilities. AROs are recorded on a discounted basis, at the time the obligation is incurred (when the pot liner is put in service) and accreted over time for the change in the present value of the liability. We capitalize the asset retirement costs by increasing the carrying amount of the related long-lived assets and depreciating these assets over their remaining useful lives.
	Certain conditional asset retirement obligations ("CAROs") related to the disposal costs of fixed assets at our primary aluminum facilities have not been recorded because they have an indeterminate settlement date.  CAROs are a legal obligation to perform an asset retirement activity in which the timing and (or) method of settlement are conditional on a future event that may or may not be within our control. We would recognize a CARO in the period in which sufficient information exists to reasonably estimate the fair value of the liability. These CAROs relate to the remediation of our primary aluminum facilities for certain regulated assets and hazardous material, such as landfills and asbestos and various other materials.
Concentration of Credit Risk	Concentrations of Credit Risk — Financial instruments, which potentially expose us to concentrations of credit risk, consist principally of trade receivables.  Our limited customer base increases our concentrations of credit risk with respect to trade receivables. We routinely assess the financial strength of our customers and collectability of our trade receivables.
Use of Estimates	Use of Estimates — The preparation of financial statements in conformity with generally accepted accounting principles in the United States ("GAAP") requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Share-Based Compensation	Share-Based Compensation — We measure the cost of employee services received in exchange for an award of equity instruments based on the grant-date fair value of the award. We recognize the cost over the period during which an employee is required to provide service in exchange for the award—the requisite service period (usually the vesting period). No compensation cost is recognized for equity instruments for which employees do not render the requisite service.
	The grant-date fair value of service-based share awards is equal to the closing stock price on the date of the grant. Stock option grant-date fair value is estimated using the Black-Scholes option-pricing model adjusted for the unique characteristics of those instruments. We have not issued any stock options since 2009. If an equity award is modified after the grant date, incremental compensation cost will be recognized in an amount equal to the excess of the fair value of the modified award over the fair value of the original award immediately before the modification.
	We issue shares to satisfy the requirements of our share-based compensation plans. At this time, we do not plan to issue treasury shares to support our share-based compensation plans, but we may in the future.
	We award performance units to certain officers and employees. The performance units may be settled in cash or common stock at the discretion of the Board. These awards have historically been settled in cash, and we expect that to continue.
Recently Issued Accounting Standards	Recently Issued Accounting Standards – We evaluate the impact of FASB Accounting Standards Updates ("ASUs") issued.  When the adoption or planned adoption of recently issued ASUs will potentially have a material impact on our consolidated financial position, results of operations and cash flows, we disclose the quantitative and qualitative effects of the adoption in our consolidated financial statements.
	In May 2014, the FASB and International Accounting Standards Board ("IASB") issued their final standard on revenue from contracts with customers. The standard, issued as ASU 2014-09 "Revenue From Contracts with Customers" by the FASB, outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance.
	Compared with current GAAP, the ASU requires significantly expanded disclosures about revenue recognition. The ASU is effective for Century for our fiscal year 2017 and thereafter. Early adoption is not permitted. We are currently evaluating the impact of adoption on our consolidated financial position, results of operations and cash flows.

Fair_value_measurements_Polici

Fair value measurements (Policies)	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value Level 3 Transfer Policy	It is our policy to recognize transfers into and transfers out of Level 3 as of the actual date of the event or change in circumstances that caused the transfer.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Financial Instruments	The following table provides the carrying amounts and approximate fair values (based on the last available trading data) of our 7.5% senior secured notes due 2021 (the "7.5% Notes due 2021") and our 7.5% senior unsecured notes due 2014 (the "7.5% Notes due 2014"). See Note 4 Fair value measurements for additional information about these financial instruments.
		December 31, 2014				December 31, 2013
		Carrying amount		Fair value		Carrying amount		Fair value
	7.5% Notes due 2021	$	246,888	$	256,408	$	246,528	$	244,375
	7.5% Notes due 2014	—		—		2,603		2,487

Business_acquisitions_Tables

Business acquisitions (Tables)	12 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Schedule of purchase price allocation	The following table summarizes the preliminary fair value of the assets acquired and the liabilities assumed as of the acquisition date:
		Acquisition Date Fair Value as of December 1, 2014
	Consideration:
	Purchase price	$	67,500
	Pension funding (1)	46,546
	Contingent consideration	13,780
	Economic, working capital and other closing adjustments (1)	(12,324		)
	Settlement of partnership accounts	(23,172		)
	Fair value of existing equity investment	56,723
	Total consideration	$	149,053
	Assets Acquired:
	Inventories	$	26,105
	Due from Alumax	20,786
	Prepaid and other current assets	2,527
	Intangible asset	2,580
	Pension asset (1)	30,842
	Property, plant and equipment – net	127,089
	Total assets acquired	$	209,929
	Liabilities Assumed:
	Accounts payable, trade	$	41,471
	Accrued and other current liabilities	8,335
	Accrued postretirement benefit costs (1)	2,857
	Other liabilities	8,213
	Deferred taxes	4,804
	Total liabilities assumed	$	65,680
	Goodwill	$	4,804
	-1	These amounts represents our preliminary estimates based on our current expectation of the pension, working capital, economic and other closing adjustments. These estimates are subject to review and approval by both parties. The final determination and payment of the settlement amounts is expected in the second quarter of 2015.
	The following table summarizes the fair value of the assets acquired and the liabilities assumed as of the acquisition date:
		Acquisition Date Fair Value
	Consideration:
	Cash	$	48,083
	Deferred purchase price	1,910
	Assets Acquired:
	Inventories	$	59,018
	Prepaid and other current assets	2,273
	Property, plant and equipment – net	55,520
	Total assets acquired	$	116,811
	Liabilities Assumed:
	Accrued and other current liabilities	$	43,316
	Accrued pension benefit costs	996
	Accrued postretirement benefit costs	6,544
	Other liabilities	7,476
	Deferred taxes	3,233
	Total liabilities assumed	$	61,565
	Gain on bargain purchase:	$	5,253
Acquisitions, pro forma information	The following unaudited pro forma financial information for the years ended December 31, 2014 and December 31, 2013 reflects our results of continuing operations as if the acquisition of the remaining interest in Mt. Holly had been completed on January 1, 2013. This unaudited pro forma financial information is provided for informational purposes only and is not necessarily indicative of what the actual results of operations would have been had the transactions taken place on January 1, 2013, nor is it indicative of the future consolidated results of operations or financial position of the combined companies.
		Year ended December 31,
		2014			2013
	Pro forma revenues	$	2,176,552		$	1,707,838
	Pro forma earnings (loss) from continuing operations	125,847			(38,819		)
	Pro forma earnings (loss) per common share, basic	1.3			(0.44		)
	Pro forma earnings (loss) per common share, diluted	1.29			(0.44		)
	From the acquisition date of December 1, 2014 through December 31, 2014, the revenue and earnings that were attributable to the acquired Alcoa’s 50.3% stake in Mt. Holly included in the consolidated statement of operations is as follows:
		Year ended December 31,
		2014
	Mt. Holly revenue	$	25,911
	Mt. Holly income from continuing operations (1)	3,024
	-1	The income attributable to the acquired Alcoa’s 50.3% stake in Mt. Holly excludes the gain on the fair value of the contingent consideration and the gain on remeasurement of the equity investment.
	From the acquisition date of June 1, 2013 through December 31, 2013, the revenue and earnings that were attributable to Sebree included in the consolidated statement of operations is as follows:
		Year ended December 31, 2013
	Sebree revenue	$	247,178
	Sebree income from continuing operations (1)	8,705
	-1	Our net income for the years ended December 31, 2014 and 2013, includes a non-recurring credit for the amortization of the deferred power contract liability of $5,534 and $31,031, respectively, related to the amortization of an unfavorable power contract assumed as part of the Sebree acquisition resulting in a credit to our depreciation and amortization expense within cost of goods sold on the consolidated statement of operations for the first quarter of 2014. The power contract terminated on January 31, 2014.
	The following unaudited pro forma financial information for the year ended December 31, 2013 reflects our results of continuing operations as if the acquisition of Sebree had been completed on January 1, 2012. This unaudited pro forma financial information is provided for informational purposes only and is not necessarily indicative of what the actual results of operations would have been had the transactions taken place on January 1, 2012, nor is it indicative of the future consolidated results of operations or financial position of the combined companies.
		Year ended December 31,
		2013			2012
	Pro forma revenues	$	1,662,707		$	1,755,196
	Pro forma loss from continuing operations	(83,035		)	(260,505		)
	Pro forma loss per common share, basic	(0.94		)	(2.94		)
	Pro forma loss per common share, diluted	(0.94		)	(2.94		)
Schedule of separately recognized transactions
	Amounts Recognized Separately from the Acquisition:	Line item	Amount recognized
	Amounts Due from Alumax	Accrued and other current liabilities	$	20,786
	Alumina Supply Agreements	Inventory	14,880

Fair_value_measurements_Tables

Fair value measurements (Tables)	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Schedule of valuation methodology for assets and liabilities at fair value	The following section describes the valuation methodology used to measure our financial assets and liabilities that were accounted for at fair value.
	Overview of Century’s valuation methodology
		Level	Significant inputs
	Cash equivalents	1	Quoted market prices
	Trust assets (1)	1	Quoted market prices
	Surety bonds	1	Quoted market prices
	E.ON contingent obligation	3	Quoted LME forward market, management’s estimates of the LME forward market prices for periods beyond the quoted periods and management’s estimate of future level of operations at CAKY
	Primary aluminum sales contract	3	Management’s estimates of future U.S. Midwest premium and risk-adjusted discount rates
	Midwest premium contracts	3	Management’s estimates of future U.S. Midwest premium
	-1	Trust assets are currently invested in money market funds. These trust assets are held to fund the non-qualified supplemental executive pension benefit obligations for certain of our officers.  The trust has sole authority to invest the funds in secure interest producing investments consisting of short-term securities issued or guaranteed by the United States government or cash and cash equivalents.
Financial assets and liabilities at fair value on a recurring basis	The following table sets forth our financial assets and liabilities that were accounted for at fair value on a recurring basis by the level of input within the ASC 820 fair value hierarchy.  As required by GAAP for fair value measurements and disclosures, financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement.  Our assessment of the significance of a particular input to the fair value measurement requires judgment, and may affect the valuation of fair value assets and liabilities and the placement within the fair value hierarchy levels. There were no transfers between Level 1 and 2 during the periods presented. There were no transfers into or out of Level 3 during the periods presented. It is our policy to recognize transfers into and transfers out of Level 3 as of the actual date of the event or change in circumstances that caused the transfer.
	Recurring Fair Value Measurements	As of December 31, 2014
		Level 1			Level 2			Level 3		Total
	ASSETS:
	Cash equivalents	$	137,712		$	—		$	—	$	137,712
	Trust assets	8,067			—			—		8,067
	Surety bonds	1,987			—			—		1,987
	TOTAL	$	147,766		$	—		$	—	$	147,766
	LIABILITIES:
	E.ON contingent obligation – net (1)	$	—		$	—		$	—	$	—
	TOTAL	$	—		$	—		$	—	$	—
	Recurring Fair Value Measurements	As of December 31, 2013
		Level 1			Level 2			Level 3		Total
	ASSETS:
	Cash equivalents	$	49,658		$	—		$	—	$	49,658
	Trust assets	11,151			—			—		11,151
	Surety bonds	2,002			—			—		2,002
	Midwest premium contracts	—			—			140		140
	TOTAL	$	62,811		$	—		$	140	$	62,951
	LIABILITIES:
	E.ON contingent obligation – net (1)	$	—		$	—		$	—	$	—
	Primary aluminum sales contract	—			—			140		140
	TOTAL	$	—		$	—		$	140	$	140
	-1	See Note 6 Debt for additional information about the E.ON contingent obligation.
Change in level 3 fair value measurements
	Change in Level 3 Fair Value Measurements during the years ended December 31,
		Derivative liabilities - net
		2014			2013
	Beginning balance, January 1,	$	—		$	(16,539	)
	Total gain (loss) included in earnings	(940		)	16,539
	Settlements	940			—
	Ending balance, December 31,	$	—		$	—
	Amount of gain included in earnings attributable to the change in unrealized losses relating to assets and liabilities held at December 31,	$	—		$	16,539

Derivative_and_hedging_instrum1

Derivative and hedging instruments (Tables)	12 Months Ended
	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Fair value of derivative assets and liabilities by balance sheet location	The following table provides the fair value and balance sheet classification of our derivatives:
	Fair Value of Derivative Assets and Liabilities
			December 31,
		Balance sheet location	2014			2013
	DERIVATIVE ASSETS:
	Midwest premium contracts	Prepaid and other current assets	$	—		$	140
	TOTAL		$	—		$	140
	DERIVATIVE LIABILITIES:
	Primary aluminum sales contract	Accrued and other current liabilities	$	—		$	140
	E.ON contingent obligation - net (1)	Other liabilities	—			—
	TOTAL		$	—		$	—
	-1	See Note 6 Debt for additional information about the E.ON contingent obligation.
Derivatives not designated as hedging instruments
	Derivatives not designated as hedging instruments:
		Gain (loss) recognized in income from derivatives
		Location	December 31, 2014			December 31, 2013
	E.ON contingent obligation – net	Net gain (loss) on forward and derivative contracts	$	1,412		$	16,781
	Primary aluminum sales contract	Related party sales	292			1,353
	Midwest premium contracts	Net gain (loss) on forward and derivative contracts	(1,080		)	140
	Primary aluminum sales contract	Net gain (loss) on forward and derivative contracts	(153		)	(323		)
	E.ON contingent obligation - net	Interest expense	(1,412		)	(1,412		)
Outstanding forward contracts not designed as hedging instruments	We had the following outstanding forward contracts that were not designated as hedging instruments:
		December 31, 2014		December 31, 2013
	Primary aluminum sales contract premium (tonnes) (1)	—		1,782
	Midwest premium contracts (tonnes)	—		6,000
	-1	Represents the remaining physical deliveries under the Glencore Metal Agreement.

Debt_Tables

Debt (Tables)	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Schedule of Debt
		December 31,
		2014			2013
	Debt classified as current liabilities:
	Hancock County industrial revenue bonds ("IRBs") due 2028, interest payable quarterly (variable interest rates (not to exceed 12%)) (1)	$	7,815		$	7,815
	7.5% senior unsecured notes due August 15, 2014, interest payable semiannually (2)(3)	—			2,603
	Iceland revolving credit facility (3)(4)	—			6,000
	Debt classified as non-current liabilities:
	7.5% senior secured notes due June 1, 2021, net of debt discount of $3,112 and $3,472, respectively, interest payable semiannually	246,888			246,528
	Total	$	254,703		$	262,946
	-1	The IRBs are classified as current liabilities because they are remarketed weekly and could be required to be repaid upon demand if there is a failed remarketing. The IRB interest rate at December 31, 2014 was 0.24%.
	-2	The amount outstanding was repaid upon maturity.
	-3	These items are recorded in accrued and other current liabilities based on the repayment terms and expected maturity.
	-4	Borrowings under the Iceland revolving credit facility bear variable interest based on LIBOR plus the applicable margin per annum. The interest rate at December 31, 2013 was 3.92%.
Schedule of line of credit facilities	Status of our Iceland revolving credit facility:
		December 31, 2014
	Credit Facility maximum amount	$	50,000
	Borrowing availability	49,940
	Outstanding borrowings	—
	Status of our U.S. revolving credit facility:
		December 31, 2014
	Credit facility maximum amount	$	150,000
	Borrowing availability, net of outstanding letters of credit	38,617
	Outstanding borrowings	—
	Letter of credit sub-facility amount (1)	130,000
	Outstanding letters of credit issued	111,383
	-1	In connection with the acquisition of Mt. Holly, the U.S. revolving credit facility was amended to increase the letter of credit sub-facility from $80,000 to $100,000. On December 1, 2014, we entered into an additional amendment to the U.S. revolving credit facility, increasing our letter of credit sub-facility to $130,000 for the period from December 1, 2014 through March 1, 2015.
Debt Instrument Redemption	Redemption Rights.  Prior to June 1, 2016, we may redeem the 7.5% Notes due 2021, in whole or in part, at a redemption price equal to 100% of the principal amount plus a make-whole premium, and if redeemed during the twelve-month period beginning on June 1 of the years indicated below, at the following redemption prices plus accrued and unpaid interest:
	Year	Percentage
	2016	105.62%
	2017	103.75%
	2018	101.88%
	2019 and thereafter	100.00%
Offsetting of financial instruments and derivatives	The following table provides information about the balance sheet location and gross amounts offset:
	Offsetting of financial instruments and derivatives
		Balance sheet location	31-Dec-14			31-Dec-13
	E.ON contingent obligation – principal	Other liabilities	$	(12,902	)	$	(12,902	)
	E.ON contingent obligation – accrued interest	Other liabilities	(5,291		)	(3,879		)
	E.ON contingent obligation – derivative asset	Other liabilities	18,193			16,781
			$	—		$	—

Shareholders_equity_Tables

Shareholders’ equity (Tables)	12 Months Ended
	Dec. 31, 2014
Stockholders' Equity Note [Abstract]
Common and Preferred Stock Activity	The Common and Preferred Stock Activity table below contains additional information about preferred stock conversions during 2014, 2013 and 2012:
	Common and Preferred Stock Activity:	Preferred stock		Common stock
	(in shares)	Series A convertible		Treasury	Outstanding
	Balance as of December 31, 2011	80,718		4,386,521	88,844,327
	Repurchase of common stock	—		400,000	(400,000	)
	Conversion of convertible preferred stock	(435	)	—	43,556
	Issuance for share-based compensation plans	—		—	60,754
	Balance as of December 31, 2012	80,283		4,786,521	88,548,637
	Conversion of convertible preferred stock	(663	)	—	66,244
	Issuance for share-based compensation plans	—		—	95,396
	Balance as of December 31, 2013	79,620		4,786,521	88,710,277
	Conversion of convertible preferred stock	(1,479	)	—	147,952
	Issuance for share-based compensation plans	—		—	206,353
	Balance as of December 31, 2014	78,141		4,786,521	89,064,582

Inventories_Tables

Inventories (Tables)	12 Months Ended
	Dec. 31, 2014
Inventory, Net [Abstract]
Schedule of Inventories	Inventories, at December 31, consist of the following:
		2014		2013
	Raw materials	$	78,599	$	69,776
	Work-in-process	33,941		22,183
	Finished goods	19,969		17,661
	Operating and other supplies	150,971		129,995
	Inventories (1)	$	283,480	$	239,615
	-1	Includes inventory acquired in connection with the Mt. Holly acquisition. See Note 2 Business acquisitions for additional information about the Mt. Holly acquisition.

Property_Plant_and_Equipment_T

Property, Plant, and Equipment (Tables)	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Property, plant and equipment	Property, plant and equipment, at December 31, consist of the following:
		2014			2013
	Land and improvements	$	51,748		$	16,021
	Buildings and improvements	403,784			340,609
	Machinery and equipment	1,395,221			1,464,532
	Construction in progress	182,393			221,101
		2,033,146			2,042,263
	Less accumulated depreciation	(741,928		)	(794,602		)
	Property, plant and equipment - net	$	1,291,218		$	1,247,661

Supplemental_financial_stateme1

Supplemental financial statement info (Tables)	12 Months Ended
	Dec. 31, 2014
Additional financial information disclosures [Abstract]
Components of Prepaid and other current assets
	Components of Prepaid and other current assets:	2014			2013
	Prepaid and other assets	$	19,601		$	15,051
	Income/withholding tax receivable – current	5,389			11,437
	VAT receivable	4,778			5,648
	Derivative assets	—			140
		$	29,768		$	32,276
Components of Other assets
	Components of Other assets:	2014			2013
	Investment in BHH and other equity investments	$	34,478		$	35,767
	Pension asset related to Mt. Holly	30,842			—
	Cash surrender value of life insurance and trust assets	26,636			27,857
	Maintenance and operating supplies – non-current	17,771			17,827
	Other assets	13,850			10,023
		$	123,577		$	91,474
Components of Accrued and other current liabilities
	Components of Accrued and other current liabilities:	2014			2013
	Accrued payable to Alcoa for Mt. Holly acquisition	$	39,208		$	—
	Accrued compensation and related benefits	19,602			11,829
	Income taxes payable	14,302			6,198
	Other accrued and current liabilities	10,573			14,842
	Accrued vacation pay	9,101			9,135
	Asset retirement obligations – current	6,006			4,230
	Deferred tax liability – current	2,241			1,555
	Accrued severance pay	2,050			11,438
	Accrued bond interest	1,563			1,636
	Revolving credit facility	—			6,000
	Current portion of long-term debt	—			2,603
		$	104,646		$	69,466
Components of Other liabilities
	Components of Other liabilities:	2014			2013
	Asset retirement obligations – non-current	$	30,944		$	22,884
	Other liabilities	9,275			7,576
	Contingent consideration	5,837			—
	Accrued workers’ compensation cost – non-current	7,216			7,283
	E.ON contingent liability and accrued interest	—			—
		$	53,272		$	37,743
Components of Accumulated Other Comprehensive Loss
	Components of Accumulated Other Comprehensive Loss:	2014			2013
	Defined benefit plan liabilities	$	(128,664	)	$	(92,177	)
	Equity in investee other comprehensive income (1)	—			(12,650		)
	Unrealized loss on financial instruments	(1,249		)	(1,064		)
	Other comprehensive loss before income tax effect	(129,913		)	(105,891		)
	Income tax effect (2)	12,231			14,059
	Accumulated other comprehensive loss	$	(117,682	)	$	(91,832	)
	-1	The amount includes our equity in the other comprehensive income of Mt. Holly until it was acquired.
	-2	The allocation of the income tax effect to the components of other comprehensive income is as follows:
		2014			2013
	Defined benefit plan liabilities	$	12,812		$	14,256
	Equity in investee other comprehensive income	—			418
	Unrealized loss on financial instruments	(581		)	(615		)
	The following table summarizes the changes in the accumulated balances for each component of accumulated other comprehensive loss ("AOCI"):
		Defined benefit plan and other postretirement liabilities			Equity in investee other comprehensive income			Unrealized loss on financial instruments			Total, net of tax
	Balance, December 31, 2011	$	(124,948	)	$	(7,918	)	$	(1,722	)	$	(134,588	)
	Other comprehensive income (loss) before reclassifications	(16,691		)	(4,306		)	(218		)	(21,215		)
	Net amount reclassified to net loss	4,198			—			413			4,611
	Balance, December 31, 2012	(137,441		)	(12,224		)	(1,527		)	(151,192		)
	Other comprehensive income (loss) before reclassifications	56,795			(8		)	—			56,787
	Net amount reclassified to net loss	2,725			—			(152		)	2,573
	Balance, December 31, 2013	(77,921		)	(12,232		)	(1,679		)	(91,832		)
	Other comprehensive income (loss) before reclassifications	(42,926		)	(419		)	—			(43,345		)
	Net amount reclassified to net income	4,995			—			(151		)	4,844
	Elimination of equity in investee resulting from acquisition	—			12,651			—			12,651
	Balance, December 31, 2014	$	(115,852	)	$	—		$	(1,830	)	$	(117,682	)
Reclassification out of AOCI	Reclassifications out of AOCI were included in the consolidated statements of operations as follows:
			Gains (Losses) Reclassified from AOCI to the Consolidated Statements of Operations
	AOCI Components	Location	2014			2013			2012
	Defined benefit plan and other postretirement liabilities	Cost of goods sold	$	6,237		$	3,264		$	4,670
		Selling, general and administrative expenses	569			990			1,055
		Income tax expense	(1,811		)	(1,529		)	(1,527		)
		Net of tax	$	4,995		$	2,725		$	4,198
	Equity in investee other comprehensive income	Cost of goods sold	$	—		$	—		$	—
		Income tax expense	(419		)	(70		)	(70		)
		Net of tax	$	(419	)	$	(70	)	$	(70	)
	Unrealized loss on financial instruments	Cost of goods sold	$	(185	)	$	(186	)	$	381
		Income tax expense	34			34			32
		Net of tax	$	(151	)	$	(152	)	$	413

Pension_and_Other_Postretireme1

Pension and Other Postretirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Schedule of Changes in Projected Benefit Obligations	The change in benefit obligations and change in plan assets as of December 31 are as follows:
		Pension							OPEB
		2014			2013				2014			2013
	Change in benefit obligation:
	Benefit obligation at beginning of year	$	238,319		$	174,954			$	134,652		$	149,263
	Service cost	5,605			4,735				1,591			2,527
	Interest cost	11,629			8,908				6,420			5,681
	Plan amendments	(5,308		)	—				—			—
	Medicare Part D	—			—				273			—
	Actuarial loss (gain)	32,772			(21,539		)		17,669			(24,170		)
	Acquisition	84,743			82,988				2,857			6,544
	Benefits paid	(11,895		)	(11,727		)		(4,681		)	(5,193		)
	Settlements	(19,573		)	—				—			—
	Benefit obligation at end of year	$	336,292		$	238,319			$	158,781		$	134,652
Schedule of Changes in Fair Value of Plan Assets
		Pension							OPEB
		2014			2013				2014			2013
	Change in plan assets:
	Fair value of plan assets at beginning of year	$	199,304		$	96,234			$	—		$	—
	Actual return on plan assets	16,118			21,675				—			—
	Acquisition	115,982			81,992				—			—
	Employer contributions	5,584			11,130				4,681			5,193
	Benefits paid	(11,895		)	(11,727		)		(4,681		)	(5,193		)
	Settlements	(19,573		)	—				—			—
	Fair value of assets at end of year	$	305,520		$	199,304			$	—		$	—
Schedule of Amounts Recognized in Balance Sheet
		Pension							OPEB
		2014			2013				2014			2013
	Funded status of plans:
	Funded status	$	(30,772	)	$	(39,015	)		$	(158,781	)	$	(134,652	)
	Amounts recognized in the Consolidated Balance Sheets:
	Non-current assets	$	30,842		$	2,547			$	—		$	—
	Current liabilities	(1,744		)	(1,714		)		(6,118		)	(5,368		)
	Non-current liabilities	(59,870		)	(39,848		)		(152,663		)	(129,284		)
	Net amount recognized	$	(30,772	)	$	(39,015	)		$	(158,781	)	$	(134,652	)
	Amounts recognized in accumulated other comprehensive loss (pre-tax):
	Net loss	$	63,360		$	45,642			$	79,720		$	65,754
	Prior service cost (benefit)	1,335			376				(15,751		)	(19,595		)
		$	64,695		$	46,018			$	63,969		$	46,159
Schedule of Accumulated and Projected Benefit Obligations	Our pension plans’ projected benefit obligation, accumulated benefit obligation, and fair value of plan assets as of December 31 are as follows:
		Projected Benefit Obligation							Accumulated Benefit Obligation							Fair Value of Plan assets
		2014			2013				2014			2013				2014			2013
	Sebree hourly pension plan	$	90,320		$	80,369			$	90,320		$	80,369			$	84,432		$	82,916
	CAWV hourly pension plan	61,989			66,866				61,989			66,852				55,273			64,905
	Salaried pension plan	71,017			66,686				68,247			60,870				49,367			51,483
	CASC pension plan	85,605			—				82,556			—				116,448			—
	SERB plan	27,361			24,398				25,851			23,369				—			—
	Total	$	336,292		$	238,319			$	328,963		$	231,460			$	305,520		$	199,304
Schedule of Net Benefit Cost	Net Periodic Benefit Cost:
		Year Ended December 31,
		Pension										OPEB
		2014			2013			2012				2014			2013			2012
	Service cost	$	5,605		$	4,735		$	2,802			$	1,591		$	2,527		$	1,790
	Interest cost	11,629			8,908			6,871				6,420			5,681			5,512
	Expected return on plan assets	(14,694		)	(10,592		)	(6,962		)		—			—			—
	Amortization of prior service costs	77			113			137				(3,844		)	(3,995		)	(4,250		)
	Amortization of net loss	1,907			3,152			3,642				3,704			5,022			6,195
	Net periodic benefit cost	4,524			6,316			6,490				7,871			9,235			9,247
	Settlements	4,701			—			—				—			—			—
	Curtailment cost	263			(18		)	—				—			(20		)	—
	Total net periodic benefit cost	$	9,488		$	6,298		$	6,490			$	7,871		$	9,215		$	9,247
Schedule of Amounts Recognized in Other Comprehensive Income (Loss)	Other changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Loss (pre-tax):
		Year Ended December 31,
		Pension							OPEB
		2014			2013				2014			2013
	Net loss (gain)	$	24,326		$	(32,624	)		$	17,669		$	(24,171	)
	Prior service cost (benefit)	1,299			—				—			—
	Amortization of net loss, including recognition due to settlement	(6,608		)	(3,152		)		(3,704		)	(5,022		)
	Amortization of prior service benefit (cost), including recognition due to curtailment	(340		)	(95		)		3,844			4,015
	Total amount recognized in other comprehensive loss	18,677			(35,871		)		17,809			(25,178		)
	Net periodic benefit cost	9,488			6,298				7,871			9,215
	Total recognized in net periodic benefit cost and other comprehensive loss	$	28,165		$	(29,573	)		$	25,680		$	(15,963	)
Schedule of Amounts in Accumulated Other Comprehensive Income (Loss) to be Recognized over Next Fiscal Year
	Amounts in accumulated other comprehensive loss expected to be recognized as components of net periodic benefit cost during 2015:
		Pension				OPEB
	Amortization of net loss	$	3,601			$	4,712
	Amortization of prior service cost (benefit)	99				(3,845		)
Weighted average assumptions used in calculating benefit obligation and net periodic benefit cost	Weighted average assumptions used to determine benefit obligations at December 31:
		Pension			OPEB
		2014	2013		2014	2013
	Discount rate	4.05%	4.89%		4.00%	4.99%
	Rate of compensation increase (1)	3%/4%	3%/4%		3%/4%	3%/4%
	Measurement date	12/31/14	12/31/13		12/31/14	12/31/13
	-1	The rate of compensation increase is 3% per year for first four years and 4% per year for year five and thereafter.
	Weighted average assumptions used to determine net periodic benefit cost for the years ended December 31:
		Pension							OPEB
		2014		2013		2012			2014		2013		2012
	Measurement date	12/31/13		12/31/12		12/31/11			12/31/13		12/31/12		12/31/11
	Fiscal year end	12/31/14		12/31/13		12/31/12			12/31/14		12/31/13		12/31/12
	Discount rate	4.89	%	4	%	4.25	%		4.99	%	4.01	%	3.83	%
	Rate of compensation increase (1)	3%/4%		3%/4%		3%/4%			3%/4%		3%/4%		3%/4%
	Expected return on plan assets	7.25	%	7.25	%	8	%		—		—		—
	-1	For 2014, the rate of compensation increase is 3% per year for first four years and 4% per year for year five and thereafter. For 2013 and 2012, the rate of compensation increase is 3% per year for first five years and 4% per year for year six and thereafter.
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates	A one-percentage-point change in the assumed health care cost trend rate would have had the following effects in 2014:
		1% Increase				1% Decrease
	Effect on total of service and interest cost	$	1,258			$	(1,019	)
	Effect on accumulated postretirement benefit obligation	24,815				(20,140		)
Schedule of Matching Contribution to Defined Contribution Plans	Employee and matching contributions are considered fully vested immediately upon participation in the plan.
		2014			2013			2012
	Company matching contribution to defined contribution (401(k)) plans	$	1,547		$	1,138		$	748
Schedule of Allocation of Plan Assets	The Pension Plans’ long-term strategic asset allocation policy targets are as follows:
		Pension Plan Asset Allocation
		Policy Target		December 31, 2014		December 31, 2013
	Equities:
	U.S. equities	50	%	42	%	43	%
	International equities	15	%	18	%	20	%
	Fixed income	35	%	40	%	37	%
				100	%	100	%
	Fair Value of Pension Plans’ assets included under the fair value hierarchy:
	As of December 31, 2014	Level 1			Level 2			Level 3			Total
	Equities:
	U.S. equities	$	79,148		$	—		$	—		$	79,148
	International equities	33,720			—			—			33,720
	Fixed income	76,204			—			—			76,204
	Plan receivable (1)	—			—			116,448			116,448
	Total	$	189,072		$	—		$	116,448		$	305,520
	As of December 31, 2013
	Equities:
	U.S. equities	$	86,323		$	—		$	—		$	86,323
	International equities	40,093			—			—			40,093
	Fixed income	72,888			—			—			72,888
	Total	$	199,304		$	—		$	—		$	199,304
	-1	Represents the receivable to the Century Aluminum of South Carolina defined benefit plan related to pension funding obligations under the Stock Purchase Agreement. Amount is subject to final approval by the parties which is expected in the second quarter of 2015.
Schedule Of Expected Benefit Plan Contributions	We expect to make the following contributions for 2015:
		2015
	Expected pension plan contributions	$	5,306
	Expected OPEB benefits payments	6,118
Schedule of Expected Benefit Payments	The following table provides the estimated future benefit payments for the pension and other postretirement benefit plans:
		Pension Benefits				OPEB Benefits
	2015	$	17,487			$	6,118
	2016	17,965				6,605
	2017	18,191				7,212
	2018	19,958				7,691
	2019	19,830				8,216
	2020 – 2024	97,247				43,357
Schedule of Multiemployer Plans	Century’s participation in the plan for the year ended December 31, 2014, is outlined in the table below.
	Fund	Steelworkers Pension Trust
	EIN / PN	23-6648508/499
	Pension Protection Act Zone Status 2014 (1)	Green
	Pension Protection Act Zone Status 2013 (1)	Green
	Subject to Financial Improvement/Rehabilitation Plan	No
	Contributions of Century Aluminum 2014	$2,164
	Contributions of Century Aluminum 2013	$2,171
	Contributions of Century Aluminum 2012	$2,282
	Withdrawal from Plan Probable	No
	Surcharge Imposed	No
	Expiration Date of Collective Bargaining Agreement	April 1, 2015
	-1	The most recent Pension Protection Act zone status available in 2014 and 2013 is for the plan's year-end December 31, 2013 and December 31, 2012, respectively.  The zone status is based on information that Century received from the plan as well as publicly available information per the Department of Labor and is certified by the plan’s actuary. Among other factors, plans in the green zone are at least 80 percent funded.

Share_Based_Compensation_Table

Share Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2014
Share-based Compensation [Abstract]
Options, fully vested and exercisable	A summary of activity under our Stock Incentive Plan during the year ended December 31, 2014 is presented below:
	Options	Number		Weighted Average Exercise Price			Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value
	Outstanding at January 1, 2014	619,833		$	24.77
	Exercised	(61,495	)	6.55
	Forfeited/expired	(14,167	)	23.76
	Outstanding, fully vested and exercisable at December 31, 2014 (1)	544,171		$	26.85		2.78	$	3,794
	-1	As the result of actions in 2011 that were determined to be a "change of control" under the Stock Incentive Plan, all options will remain exercisable for their respective remaining term, regardless of whether the awardees remain employees of Century.
Service-based share awards activity
	Service-based share awards
	Outstanding at January 1, 2014	442,737
	Granted	258,662
	Vested	(200,965	)
	Forfeited	(35,949	)
	Outstanding at December 31, 2014	464,485
		Year ended December 31,
		2014			2013			2012
	Weighted average per share fair value of service-based share grants	$	15.31		$	8.19		$	8.14
	Total intrinsic value of option exercises	1,011			13			—
Share-based compensation expense	The following table summarizes the compensation cost recognized for the years ended December 31, 2014, 2013 and 2012 for all options, service-based share and performance-based share awards.  No share-based compensation cost was capitalized during these periods and there were no significant modifications (other than the accelerated vesting in 2011 described above) of any share-based awards in 2014, 2013 and 2012.
		Year ended December 31,
		2014			2013			2012
	Share-based compensation expense reported:
	Performance-based share expense	$	1,090		$	475		$	27
	Service-based share expense	244			603			586
	Stock option expense	—			—			—
	Total share-based compensation expense before income tax	1,334			1,078			613
	Income tax	—			—			—
	Total share-based compensation expense, net of income tax	$	1,334		$	1,078		$	613

Earnings_per_share_Tables

Earnings per share (Tables)	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Basic and diluted earnings (loss) per share	The following table shows the basic and diluted earnings (loss) per share for 2014, 2013, and 2012:
		For the year ended December 31, 2014
		Net income			Shares (000)		Per-Share
	Net income	$	112,494
	Amount allocated to common stockholders	91.81		%
	Basic EPS:
	Net income allocated to common stockholders	103,283			88,823		$	1.16
	Effect of Dilutive Securities:
	Share-based compensation plans				605
	Diluted EPS:
	Net income allocated to common stockholders with assumed conversion	$	103,283		89,428		$	1.15
		For the year ended December 31, 2013
		Net loss			Shares (000)		Per-Share
	Net loss	$	(40,313	)
	Amount allocated to common stockholders (1)	100		%
	Basic and Diluted EPS:
	Net loss allocated to common stockholders	$	(40,313	)	88,612		$	(0.45	)
		For the year ended December 31, 2012
		Net loss			Shares (000)		Per-Share
	Net loss	$	(35,610	)
	Amount allocated to common stockholders (1)	100		%
	Basic and Diluted EPS:
	Net loss allocated to common stockholders	$	(35,610	)	88,534		$	(0.40	)
	-1	We have not allocated net losses between common and preferred stockholders, as the holders of our preferred shares do not have a contractual obligation to share in the loss.
Antidilutive securities excluded from calculation of diluted EPS
	Securities excluded from the calculation of diluted EPS:
		2014		2013		2012
	Stock options (1)	320,553		619,833		626,334
	Service-based share awards (1)	—		442,737		396,133
	-1	In periods when we report a net loss, all share awards are excluded from the calculation of diluted weighted average shares outstanding because of their antidilutive effect on earnings (loss) per share.

Income_taxes_Tables

Income taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Components of pre-tax book income (loss)
	The components of pre-tax book income (loss) consist of the following:
		Year Ended December 31,
		2014			2013			2012
	U.S.	$	77,046		$	(47,080	)	$	(38,762	)
	Foreign	52,451			7,236			9,439
	Total	$	129,497		$	(39,844	)	$	(29,323	)
Significant components of the income before income tax expense
	Significant components of the income tax expense consist of the following:
		Year Ended December 31,
		2014			2013			2012
	Current:
	U.S. federal current expense (benefit)	$	(112	)	$	532		$	(161	)
	State current expense (benefit)	2,252			(445		)	(669		)
	Foreign current expense	15,098			6,198			9,808
	Total current expense	17,238			6,285			8,978
	Deferred:
	U.S. federal deferred benefit	(1,696		)	(3,905		)	(1,564		)
	State deferred benefit	(12		)	(207		)	—
	Foreign deferred tax expense	2,778			958			1,496
	Total deferred benefit	1,070			(3,154		)	(68		)
	Total income tax expense	$	18,308		$	3,131		$	8,910
Reconciliation of the statutory U.S. Federal income tax rate to the effective income tax rate on income (loss)
	A reconciliation of the statutory U.S. Federal income tax rate to the effective income tax rate on income (loss) is as follows:
		2014		2013		2012
	Federal Statutory Rate	35	%	35	%	35	%
	Permanent differences	4.3		54.5		12.6
	State taxes, net of Federal benefit	(6.3	)	97.2		0.1
	Foreign earnings taxed at different rates than U.S.	(0.5	)	17.4		(369.5	)
	Valuation allowance	(25.4	)	(265.9	)	297.6
	Changes in uncertain tax reserves	0.6		40.5		(6.7	)
	Other	6.4		13.4		0.5
	Effective tax rate	14.1	%	(7.9	)%	(30.4	)%
Significant components of deferred tax assets and liabilities	Significant components of our deferred tax assets and liabilities as of December 31 are as follows:
		2014			2013
	Deferred tax assets:
	Accrued postretirement benefit cost	$	15,683		$	12,851
	Accrued liabilities	4,494			2,355
	Share-based compensation	7,350			5,327
	Derivative and hedging contracts	58,687			116,550
	Goodwill	10,521			12,421
	Equity contra - other comprehensive loss	81,567			61,216
	Dual consolidated losses and capital losses	7,509			14,512
	Net operating losses and tax credits	646,158			637,721
	Foreign basis differences	668			—
	Other	1,239			1,533
	Total deferred tax assets	833,876			864,486
	Valuation allowance	(748,283		)	(765,023		)
	Net deferred tax assets	$	85,593		$	99,463
	Deferred tax liabilities:
	Tax over financial statement depreciation	$	(142,627	)	$	(145,945	)
	Pension	(14,222		)	(11,543		)
	Unremitted foreign earnings	(30,308		)	(35,344		)
	Foreign basis differences	—			(790		)
	Total deferred tax liabilities	(187,157		)	(193,622		)
	Net deferred tax liability	$	(101,564	)	$	(94,159	)
Changes in valuation allowance	The changes in the valuation allowance are as follows:
		2014			2013
	Beginning balance, valuation allowance	$	765,023		$	656,352
	Change in valuation allowance	(16,740		)	108,671
	Ending balance, valuation allowance	$	748,283		$	765,023
Significant components of Net Operating Loss Carryforwards	The significant components of our NOL carryforwards are as follows:
		2014			2013
	Federal (1)	$	1,306,482		$	1,287,118
	State (2)	2,078,105			2,077,890
	Foreign (3)	446,234			459,457
	-1	The federal NOL begins to expire in 2028.
	-2	The state NOLs begin to expire in 2027.
	-3	The Icelandic NOL begins to expire in 2017; Dutch NOL begins to expire in 2022.
Reconciliation of beginning and ending amounts of gross unrecognized tax benefits	A reconciliation of the beginning and ending amounts of gross unrecognized tax benefits (excluding interest) is as follows:
		2014			2013			2012
	Balance as of January 1,	$	1,200		$	17,600		$	15,900
	Additions based on tax positions related to the current year	1,100			700			2,700
	Decreases due to lapse of applicable statute of limitations	(300		)	(2,800		)	(800		)
	Settlements	—			(14,300		)	(200		)
	Balance as of December 31,	$	2,000		$	1,200		$	17,600
Significant components of unrecognized tax positions	The components of our unrecognized tax positions are as follows:
		2014			2013			2012
	Highly certain tax positions	$	1,900		$	1,100		$	16,900
	Other unrecognized tax benefits	100			100			700
	Gross unrecognized tax benefits	$	2,000		$	1,200		$	17,600
	Accrued interest and penalties related to unrecognized tax benefits	$	—		$	100		$	100

Forward_delivery_contracts_and1

Forward delivery contracts and financial instruments (Tables)	12 Months Ended
	Dec. 31, 2014
Forward Delivery Contracts and Financial Instruments [Abstract]
Schedule of Forward Physical Delivery Agreements	Forward Physical Delivery Agreements
	Primary Aluminum Sales Contracts
	Contract	Customer	Volume	Term	Pricing
	Glencore Grundartangi Metal Agreement (1)	Glencore	All primary aluminum produced at Grundartangi, net of tolling and other sales commitments	January 1, 2014 through December 31, 2017	Variable, based on LME and European Duty Paid premium and product premiums, as applicable
	-1	The Glencore Grundartangi Metal Agreement is for all metal produced at Grundartangi from 2014 through 2017 less commitments under existing tolling and other sales contracts.  Grundartangi currently estimates that it will sell Glencore approximately 205,000 tonnes of aluminum under this agreement in 2015.
	See Note 22 Subsequent events for additional information about a new aluminum supply agreement with Glencore.
	Tolling Contracts
	Contract	Customer	Volume	Term	Pricing
	Glencore Toll Agreement	Glencore	90,000 tonnes per year ("tpy")	Through July 2016	Variable, based on LME and European Duty Paid premium
	Apart from the Glencore Grundartangi Metal Agreement, the Southwire Metal Agreement (which expired at the end of 2014) and the Glencore Sweep Agreement (a contract for all metal produced in the U.S. in 2013, less existing sales agreements and valued-added metal sales, which expired at the end of 2013), we had the following forward delivery contractual commitments:
	Other forward delivery contracts
		December 31, 2014		December 31, 2013
		(in tonnes)
	Other forward delivery contracts – total	6,108		118,373
	Other forward delivery contracts – Glencore	4,058		20,008

Asset_retirement_obligations_A1

Asset retirement obligations (“ARO”) (Tables)	12 Months Ended
	Dec. 31, 2014
Asset Retirement Obligation Disclosure [Abstract]
Schedule of changes in asset retirement obligations	The reconciliation of the changes in the asset retirement obligations is presented below:
		Year ended December 31,
		2014			2013
	Beginning balance, ARO liability	$	27,113		$	16,124
	Additional ARO liability incurred	2,548			1,730
	ARO liabilities settled	(4,731		)	(2,580		)
	Accretion expense	1,517			1,733
	Additional ARO liability from Sebree acquisition	—			10,106
	Additional ARO liability from Mt. Holly acquisition	10,503			—
	Ending balance, ARO liability	$	36,950		$	27,113

Supplemental_cash_flow_informa1

Supplemental cash flow information (Tables)	12 Months Ended
	Dec. 31, 2014
Supplemental Cash Flow Information [Abstract]
Supplemental Cash Flow Information
		Year Ended December 31,
		2014		2013		2012
	Cash paid for:
	Interest	$	19,066	$	20,539	$	20,212
	Income/withholding taxes (1)	12,189		28,654		41,455
	Non-cash investing activities:
	Accrued capital costs	$	744	$	9,409	$	(683	)
	-1	We paid withholding taxes in Iceland on intercompany dividends of $5,491, $18,067 and $22,633 during the years ended December 31, 2014, 2013 and 2011, respectively. Our tax payments in Iceland for withholding taxes, income taxes and any associated refunds are denominated in ISK.

Quarterly_Information_Unaudite1

Quarterly Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Data [Abstract]
Schedule of Quarterly Financial Information	Financial results by quarter for the years ended December 31, 2014 and 2013 are as follows:
		Net sales		Gross profit (loss)			Net income (loss)			Net income (loss) allocated to common stockholders			Basic			Diluted earnings (loss) per share
													earnings (loss) per share
	2014
	4th Quarter (1)	$	551,239	$	89,996		$	61,849		$	56,824		$	0.64		$	0.63
	3rd Quarter (2)	500,632		75,714			50,405			46,277			0.52			0.52
	2nd Quarter (3)	458,324		38,504			20,344			18,675			0.21			0.21
	1st Quarter (4)	420,847		(1,758		)	(20,104		)	(20,104		)	(0.23		)	(0.23		)
	2013
	4th Quarter (5)	$	401,174	$	15,285		$	(9,675	)	$	(9,675	)	$	(0.11	)	$	(0.11	)
	3rd Quarter (6)	399,928		12,354			(9,507		)	(9,507		)	(0.11		)	(0.11		)
	2nd Quarter (7)	331,937		(5,698		)	(29,384		)	(29,384		)	(0.33		)	(0.33		)
	1st Quarter (8)	321,274		17,582			8,253			7,567			0.09			0.09
	-1	The fourth quarter of 2014 net income included a benefit of $7,943 for the gain on remeasurement of contingent consideration and a benefit of $1,318 for gain on remeasurement of our equity investment in Mt. Holly. Results were negatively impacted by $4,964 in non-cash, non-recurring pension charges and by $2,616 related to the separation of former senior executives.
	-2	The third quarter of 2014 net income reflects higher aluminum prices and lower power prices in the Midwestern U.S.
	-3	The second quarter of 2014 net income reflects higher aluminum prices and lower power prices in the Midwestern U.S. Results were negatively impacted by a charge of $500 for the finalization of a legal settlement.
	-4	The first quarter of 2014 cost of sales included a benefit of $5,534 related to deferred power contract liability amortization. Results were negatively impacted by a $3,100 charge for increased legal reserves.
	-5	The fourth quarter of 2013 cost of sales included a benefit of $16,570 related to deferred power contract liability amortization. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a credit of $9,040. The financial results also include an $8,400 charge relating to the separation of our former CEO.
	-6	The third quarter of 2013 cost of sales included an $11,720 benefit for deferred power contract liability amortization. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a credit of $5,762.
	-7	The second quarter of 2013 amounts differ from our reported second quarter results due to purchase price accounting adjustments related to the Sebree acquisition which were retroactively applied to the second quarter of 2013. The second quarter of 2013 net loss included a gain on bargain purchase of $5,253 and power contract amortization of $2,741 associated with the Sebree acquisition. Results were negatively impacted by a charge of $3,272 for the early extinguishment of our 8.0% Notes and a charge for severance and other expenses of $1,750 related to our corporate headquarters relocation. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a charge of $10,211.
	-8	The first quarter of 2013 net income included a net benefit of $2,225 related to a litigation reserve adjustment and an unrealized gain of $15,722 related to a LME-based contingent obligation. Results were negatively impacted by severance and other expenses of $2,213 related to our corporate headquarters relocation. The net effect of reporting inventory on a lower of cost or market basis was a charge to cost of goods sold of $5,838 in the quarter.

Business_Segments_Tables

Business Segments (Tables)	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Reconciliation of assets from segment to consolidated	A reconciliation of our consolidated assets to the total of primary aluminum segment assets is provided below.
	Segment assets (1)	2014		2013		2012
	Primary	$	1,971,900	$	1,770,749	$	1,730,321
	Corporate, unallocated	42,135		39,447		46,005
	Total assets	$	2,014,035	$	1,810,196	$	1,776,326
	-1	Segment assets include accounts receivable, due from affiliates, prepaid and other current assets, inventory, intangible assets and property, plant and equipment — net; the remaining assets are unallocated corporate assets.
Schedule of revenue from external customers and long-lived assets, by geographical areas	Included in the consolidated financial statements are the following amounts related to geographic locations:
		2014		2013		2012
	Net sales:
	United States	$	1,370,570	$	1,022,081	$	821,976
	Iceland	560,472		432,232		450,135
	Long-lived assets: (1)
	United States	$	487,536	$	392,424	$	368,897
	Iceland	831,507		853,636		869,809
	Other	95,752		93,075		50,223
	-1	Includes long-lived assets other than financial instruments.
Schedule of revenue by major customers by reporting segments	The following table shows our major customers whose sales revenue exceeded 10% of our net sales.  A loss of any of these customers could have a material adverse effect on our results of operations.  The net sales revenue for these customers is as follows:
		Year Ended December 31,
		2014		2013		2012
	Glencore	$	1,262,101	$	511,051	$	552,299
	Southwire	226,740		312,102		346,311
	RTA	—		223,353		—
	BHP Billiton	—		191,445		202,500

Related_Party_Transactions_Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2014
Related Party Transactions [Abstract]
Schedule of Related Party Transactions	A summary of the aforementioned related party transactions for the years ended December 31, 2014, 2013 and 2012 is as follows:
		Year Ended December 31,
		2014		2013		2012
	Net sales to Glencore	$	1,262,101	$	511,051	$	552,299
	Purchases from Glencore	285,167		173,693		145,589
	Purchases from BHH	47,804		86,678		39,337

Recovered_Sheet2

Summary of significant accounting policies Schedule of Equity Method Investment, Equity method investee (Details)	Dec. 31, 2014
Mt. Holly Partnership Aluminum Reduction Facility [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	49.70%
Mt. Holly Property, Plant and Equipment Owned By Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	49.70%
Baise Haohi Carbon Co Ltd [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	40.00%

Summary_of_significant_account2

Summary of significant accounting policies Summary of significant accounting policies (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Accounting Policies [Abstract]
Glencore beneficial ownership	41.80%
Glencore economic ownership	46.50%
Allowance for doubtful accounts receivable	$1,000	$734

Summary_of_significant_account3

Summary of significant accounting policies Schedule of Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2014
Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life minimum (in years)	10
Estimated useful life maximum (in years)	45
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life minimum (in years)	5
Estimated useful life maximum (in years)	35

Summary_of_significant_account4

Summary of significant accounting policies Long-term Debt Instruments (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Thousands, unless otherwise specified
Debt Instrument [Line Items]
Carrying amount of current portion of long term debt	$0		$2,603
Senior secured notes due June 01, 2021 [Member]
Debt Instrument [Line Items]
Interest rate (as a percent)	7.50%
Senior unsecured notes due August 15, 2014 [Member]
Debt Instrument [Line Items]
Interest rate (as a percent)	7.50%
Long-term Debt [Member] | Senior secured notes due June 01, 2021 [Member]
Debt Instrument [Line Items]
Carrying amount of secured long term debt	246,888		246,528
Fair value of long term debt	256,408		244,375
Interest rate (as a percent)	7.50%		7.50%
Short-term Debt [Member] | Senior unsecured notes due August 15, 2014 [Member]
Debt Instrument [Line Items]
Carrying amount of current portion of long term debt	0	[1],[2]	2,603
Fair value of current portion of long term debt	$0		$2,487
Interest rate (as a percent)	7.50%		7.50%
[1]	The amount outstanding was repaid upon maturity.
[2]	These items are recorded in accrued and other current liabilities based on the repayment terms and expected maturity.

Business_acquisitions_Acquisit

Business acquisitions Acquisition of Mt. Holly aluminum smelter additional (Details) (Mt. Holly Smelter [Member])	Dec. 01, 2014
	t
Mt. Holly Smelter [Member]
Business Acquisition [Line Items]
Percentage of voting interests acquired (percentage)	50.30%
Percentage of ownership after acquisition (percentage)	100.00%
Employees	600
Primary aluminum capacity (in tonnes)	231,000
Equity interest in acquiree (percentage)	49.70%

Business_acquisitions_Acquisit1

Business acquisitions Acquisition of Mt. Holly aluminum smelter (Details) (USD $)	3 Months Ended	12 Months Ended				0 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012	Dec. 01, 2014
Business Acquisition [Line Items]
Purchase price cash paid		$1,042		$48,058	$0
Gain on fair value of contingent consideration	7,943	7,943		0	0
Gain on remeasurement of equity investment	1,318	1,318		0	0
Contingent consideration	5,837	5,837		0
Pension asset (1)	30,842	30,842		0
Mt. Holly Smelter [Member]
Business Acquisition [Line Items]
Purchase price cash paid		53,831
Acquisition-related costs	1,087	1,087
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High						22,500
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, Low						12,500
Gain on fair value of contingent consideration		7,943
Gain on remeasurement of equity investment		1,318
Purchase price						67,500
Pension funding (1)						46,546	[1]
Contingent consideration						13,780
Economic, working capital and other closing adjustments (1)						-12,324	[1]
Settlement of partnership accounts						-23,172
Fair value of existing equity investment						56,723
Total consideration						149,053
Inventories						26,105
Due from Alumax						20,786
Prepaid and other current assets						2,527
Intangible asset						2,580
Pension asset (1)						30,842	[1]
Property, plant and equipment – net						127,089
Total assets acquired						209,929
Accounts payable, trade						41,471
Accrued and other current liabilities						8,335
Accrued postretirement benefit costs						2,857	[1]
Other liabilities						8,213
Deferred taxes						4,804
Total liabilities assumed						65,680
Goodwill						4,804
Mt. Holly revenue		25,911
Mt. Holly income from continuing operations (1)		3,024	[2]
Pro forma revenues		2,176,552		1,707,838
Pro forma earnings (loss) from continuing operations		125,847		-38,819
Pro forma earnings (loss) per common share, basic		$1.30		($0.44)
Pro forma earnings (loss) per common share, diluted		$1.29		($0.44)
Amounts Due from Alumax	20,786	20,786
Alumina Supply Agreements	$14,880	$14,880
[1]	These amounts represents our preliminary estimates based on our current expectation of the pension, working capital, economic and other closing adjustments. These estimates are subject to review and approval by both parties. The final determination and payment of the settlement amounts is expected in the second quarter of 2015.
[2]	The income attributable to the acquired Alcoa’s 50.3% stake in Mt. Holly excludes the gain on the fair value of the contingent consideration and the gain on remeasurement of the equity investment.

Business_acquisitions_Sebree_e

Business acquisitions Sebree employees (Details) (Sebree Smelter [Member])	Jun. 01, 2013
Sebree Smelter [Member]
Business Acquisition [Line Items]
Employees	500

Business_acquisitions_Acquisit2

Business acquisitions Acquisition of Sebree aluminum smelter (Details) (USD $)	3 Months Ended					12 Months Ended				3 Months Ended	19 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012	Jun. 30, 2014	Dec. 31, 2014	Jun. 01, 2013
												t
Business Acquisition [Line Items]
Purchase price cash paid						$1,042	$48,058		$0
Gain on fair value of contingent consideration	7,943					7,943	0		0
Gain on bargain purchase					5,253	0	5,253		0
Sebree power contract amortization		5,534	16,570	11,720	2,741	5,534	31,031		0
Sebree Smelter [Member]
Business Acquisition [Line Items]
Primary aluminum capacity (in tonnes)												205,000
Purchase price												61,000
Purchase price cash paid											49,035
Gain on fair value of contingent consideration										965
Gain on bargain purchase											5,253
Cash											48,083
Deferred purchase price											1,910
Inventories	59,018					59,018					59,018
Prepaid and other current assets	2,273					2,273					2,273
Property, plant and equipment – net	55,520					55,520					55,520
Total assets acquired	116,811					116,811					116,811
Accrued and other current liabilities	43,316					43,316					43,316
Accrued pension benefit costs	996					996					996
Accrued postretirement benefit costs	6,544					6,544					6,544
Other liabilities	7,476					7,476					7,476
Deferred taxes	3,233					3,233					3,233
Total liabilities assumed	61,565					61,565					61,565
Sebree revenue							247,178
Sebree income from continuing operations (1)							8,705	[1]
Sebree power contract amortization						5,534	31,031
Pro forma revenues							1,662,707		1,755,196
Pro forma loss from continuing operations							($83,035)		($260,505)
Pro forma loss per common share, basic							($0.94)		($2.94)
Pro forma loss per common share, diluted							($0.94)		($2.94)
[1]	Our net income for the years ended December 31, 2014 and 2013, includes a non-recurring credit for the amortization of the deferred power contract liability of $5,534 and $31,031, respectively, related to the amortization of an unfavorable power contract assumed as part of the Sebree acquisition resulting in a credit to our depreciation and amortization expense within cost of goods sold on the consolidated statement of operations for the first quarter of 2014. The power contract terminated on January 31, 2014.

Asset_purchase_Details

Asset purchase (Details) (Carbon Anodes Production Facility [Member], USD $)	Dec. 31, 2014	Jun. 11, 2012
In Thousands, unless otherwise specified	t
Carbon Anodes Production Facility [Member]
Asset purchase [Line Items]
Assets acquired		$12,500
Century Vlissingen Anode capacity (tonnes)	75,000
Century Vlissingen Expected Anode capacity (tonnes)	150,000

Fair_value_measurements_Detail

Fair value measurements (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Derivative Liabilities - Net [Member]
Level 3 fair value measurements [Roll Forward]
Beginning balance, January 1,	$0		($16,539)
Total gain (loss) included in earnings	-940		16,539
Settlements	940		0
Ending balance, December 31,	0		0
Amount of gain included in earnings attributable to the change in unrealized losses relating to assets and liabilities held at December 31,	0		16,539
Fair Value, Measurements, Recurring [Member]
ASSETS:
Cash equivalents	137,712		49,658
Trust assets	8,067		11,151
Surety bonds	1,987		2,002
Midwest premium contracts			140
TOTAL	147,766		62,951
LIABILITIES:
E.ON contingent obligation – net (1)	0	[1]	0	[1]
Primary aluminum sales contract			140
TOTAL	0		140
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
ASSETS:
Cash equivalents	137,712		49,658
Trust assets	8,067		11,151
Surety bonds	1,987		2,002
Midwest premium contracts			0
TOTAL	147,766		62,811
LIABILITIES:
E.ON contingent obligation – net (1)	0	[1]	0	[1]
Primary aluminum sales contract			0
TOTAL	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
ASSETS:
Cash equivalents	0		0
Trust assets	0		0
Surety bonds	0		0
Midwest premium contracts			0
TOTAL	0		0
LIABILITIES:
E.ON contingent obligation – net (1)	0	[1]	0	[1]
Primary aluminum sales contract			0
TOTAL	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
ASSETS:
Cash equivalents	0		0
Trust assets	0		0
Surety bonds	0		0
Midwest premium contracts			140
TOTAL	0		140
LIABILITIES:
E.ON contingent obligation – net (1)	0	[1]	0	[1]
Primary aluminum sales contract			140
TOTAL	$0		$140
Senior secured notes due June 01, 2021 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.50%
Senior unsecured notes due August 15, 2014 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.50%
[1]	See Note 6 Debt for additional information about the E.ON contingent obligation.

Derivative_and_hedging_instrum2

Derivative and hedging instruments (Details) (Not Designated as Hedging Instrument [Member], USD $)	Dec. 31, 2014		Dec. 31, 2013
In Thousands, unless otherwise specified
Fair value of derivative assets and liabilities by balance sheet location [Abstract]
DERIVATIVE ASSETS	$0		$140
DERIVATIVE LIABILITIES	0		0
Midwest Premium Contracts [Member]
Outstanding forward contracts not designated as hedging instruments [Abstract]
Midwest premium contracts (tonnes)	0		6,000
Midwest Premium Contracts [Member] | Prepaid and Other Current Assets [Member]
Fair value of derivative assets and liabilities by balance sheet location [Abstract]
DERIVATIVE ASSETS	0		140
E.ON Contingent Obligation [Member] | Other Liabilities [Member]
Fair value of derivative assets and liabilities by balance sheet location [Abstract]
DERIVATIVE LIABILITIES	0	[1]	0	[1]
Primary Aluminum Sales Contracts [Member] | Accrued and Other Current Liabilities [Member]
Fair value of derivative assets and liabilities by balance sheet location [Abstract]
DERIVATIVE LIABILITIES	$0		$140
Primary Aluminum Sales Contract Premium [Member]
Outstanding forward contracts not designated as hedging instruments [Abstract]
Primary aluminum sales contract premium (tonnes) (1)	0	[2]	1,782	[2]
[1]	See Note 6 Debt for additional information about the E.ON contingent obligation.
[2]	Represents the remaining physical deliveries under the Glencore Metal Agreement.

Derivative_and_hedging_instrum3

Derivative and hedging instruments Part 2 (Details) (Not Designated as Hedging Instrument [Member], USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
E.ON Contingent Obligation [Member] | Net Gain (Loss) on Forward and Derivative Contracts [Member]
Derivatives not designated as hedging instruments [Abstract]
Gain (loss) recognized in income from derivatives	$1,412	$16,781
E.ON Contingent Obligation [Member] | Interest Expense [Member]
Derivatives not designated as hedging instruments [Abstract]
Gain (loss) recognized in income from derivatives	-1,412	-1,412
Midwest Premium Contracts [Member] | Net Gain (Loss) on Forward and Derivative Contracts [Member]
Derivatives not designated as hedging instruments [Abstract]
Gain (loss) recognized in income from derivatives	-1,080	140
Primary Aluminum Sales Contracts [Member] | Net Gain (Loss) on Forward and Derivative Contracts [Member]
Derivatives not designated as hedging instruments [Abstract]
Gain (loss) recognized in income from derivatives	-153	-323
Primary Aluminum Sales Contracts [Member] | Related Party Sales [Member]
Derivatives not designated as hedging instruments [Abstract]
Gain (loss) recognized in income from derivatives	$292	$1,353

Debt_Details

Debt (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Debt Instrument [Line Items]
Industrial revenue bonds	$7,815		$7,815
Current portion of long-term debt	0		2,603
Revolving credit facility	0		6,000
Debt	254,703		262,946
Industrial revenue bonds due 2028 [Member] | Short-term Debt [Member]
Debt Instrument [Line Items]
Industrial revenue bonds	7,815	[1]	7,815	[1]
Variable interest rates, maximum (as a percent)	12.00%		12.00%
Interest rate (as a percent)	0.24%
Maturity date	1-Apr-28		1-Apr-28
Net of debt discount	0		0
Senior unsecured notes due August 15, 2014 [Member]
Debt Instrument [Line Items]
Interest rate (as a percent)	7.50%
Senior unsecured notes due August 15, 2014 [Member] | Short-term Debt [Member]
Debt Instrument [Line Items]
Current portion of long-term debt	0	[2],[3]	2,603
Interest rate (as a percent)	7.50%		7.50%
Maturity date	15-Aug-14		15-Aug-14
Net of debt discount	0		0
Iceland revolving credit facility [Member] | Short-term Debt [Member]
Debt Instrument [Line Items]
Revolving credit facility	0	[3],[4]	6,000	[3],[4]
Interest rate (as a percent)			3.92%
Senior secured notes due June 01, 2021 [Member]
Debt Instrument [Line Items]
Interest rate (as a percent)	7.50%
Senior secured notes due June 01, 2021 [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Secured Long-term Debt, Noncurrent	246,888		246,528
Interest rate (as a percent)	7.50%		7.50%
Maturity date	1-Jun-21		1-Jun-21
Net of debt discount	$3,112		$3,472
[1]	The IRBs are classified as current liabilities because they are remarketed weekly and could be required to be repaid upon demand if there is a failed remarketing. The IRB interest rate at December 31, 2014 was 0.24%.
[2]	The amount outstanding was repaid upon maturity.
[3]	These items are recorded in accrued and other current liabilities based on the repayment terms and expected maturity.
[4]	Borrowings under the Iceland revolving credit facility bear variable interest based on LIBOR plus the applicable margin per annum. The interest rate at December 31, 2013 was 3.92%.

Debt_Credit_Facility_Details

Debt Credit Facility (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Long-term Debt [Member] | U.S revolving credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$150,000
Line of Credit Facility, Remaining Borrowing Capacity	38,617
Line of Credit Facility, Amount Outstanding	0
Long-term Debt [Member] | U.S. letter of credit [Member]
Line of Credit Facility [Line Items]
Line Of Credit Facility Additional Borrowings Under Letter Of Credit Sub Facility Amount	130,000	[1]
Line Of Credit Facility Additional Borrowings Under Letter Of Credit Sub Facility Original Amount	80,000	[1]
Line Of Credit Facility Additional Borrowings Under Letter Of Credit Sub Facility Future Amended Amount	100,000	[1]
Outstanding letters of credit issued under the revolving credit facility	111,383
Long-term Debt [Member] | Iceland revolving credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	50,000
Line of Credit Facility, Amount Outstanding	0
Line of Credit Facility, Prepayment terms	Grundartangi may, by giving no less than five business days prior written notice to Landsbankinn, prepay any outstanding borrowings without penalty or premium (except incurred breakage costs) in whole or in part.
Line of Credit Facility, Current Borrowing Capacity	$49,940
U.S revolving credit facility [Member] | Long-term Debt [Member]
Line of Credit Facility [Line Items]
Credit Facility, term (in years)	5 years
Short-term Debt [Member] | Iceland revolving credit facility [Member]
Line of Credit Facility [Line Items]
Credit Facility, term (in years)	3 years
[1]	In connection with the acquisition of Mt. Holly, the U.S. revolving credit facility was amended to increase the letter of credit sub-facility from $80,000 to $100,000. On December 1, 2014, we entered into an additional amendment to the U.S. revolving credit facility, increasing our letter of credit sub-facility to $130,000 for the period from December 1, 2014 through March 1, 2015.

Debt_80_Note_Details

Debt 8.0% Note (Details) (Long-term Debt [Member], Senior secured notes due May 15, 2014 [Member], USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2014
Long-term Debt [Member] | Senior secured notes due May 15, 2014 [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
Secured Long-term Debt, Noncurrent	$0	$0

Debt_75_Notes_Due_2021_Details

Debt 7.5% Notes Due 2021 (Details) (Senior secured notes due June 01, 2021 [Member], USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Jun. 04, 2013
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.50%
Long-term Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$250,000
Proceeds from Issuance of Debt	$246,330
Debt Instrument, Interest Rate, Stated Percentage	7.50%	7.50%
Debt Instrument, Collateral, Equity Interests in Foreign Subsidiaries	65.00%

Debt_75_Notes_Redemption_Detai

Debt 7.5% Notes Redemption (Details) (Long-term Debt [Member], Senior secured notes due June 01, 2021 [Member])	12 Months Ended
	Dec. 31, 2014
Debt Instrument, Redemption [Line Items]
Debt Redemptions Rights After Change Of Control	101.00%
Debt Instrument, Redemption, Period One [Member]
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
Debt Instrument, Redemption, Period Two [Member]
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	105.63%
Debt Instrument, Redemption, Period Three [Member]
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	103.75%
Debt Instrument, Redemption, Period Four [Member]
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	101.88%
Debt Instrument, Redemption, Period Five [Member]
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%

Debt_75_Notes_due_May_2014_Det

Debt 7.5% Notes due May 2014 (Details) (Senior unsecured notes due August 15, 2014 [Member], Long-term Debt [Member], USD $)	1 Months Ended
In Thousands, unless otherwise specified	Aug. 31, 2004
Senior unsecured notes due August 15, 2014 [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of Debt	$250,000

Debt_EON_contingent_obligation

Debt E.ON contingent obligation (Details) (USD $)	3 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Unrealized gain (loss) on E.ON obligation	$15,722	$1,412	$16,781	$0
E.ON Contingent Obligation		0	0
Long-term Debt [Member] | Contingent obligation [Member]
Debt Instrument [Line Items]
Payment terms		72 monthly payments
Unrealized gain (loss) on E.ON obligation		1,412	16,781
Debt Instrument, Interest Rate, Stated Percentage		10.94%
Other Liabilities [Member] | Contingent obligation [Member]
Debt Instrument [Line Items]
E.ON contingent obligation – principal		-12,902	-12,902
E.ON contingent obligation – accrued interest		-5,291	-3,879
E.ON contingent obligation – derivative asset		18,193	16,781
E.ON Contingent Obligation		$0	$0

Debt_Industrial_Revenue_Bonds_

Debt Industrial Revenue Bonds (Details) (Short-term Debt [Member], Industrial revenue bonds due 2028 [Member])	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Short-term Debt [Member] | Industrial revenue bonds due 2028 [Member]
Short-term Debt [Line Items]
Variable interest rates, maximum (as a percent)	12.00%	12.00%

Debt_Principal_payments_on_lon

Debt Principal payments on long term debt (Details) (Long-term Debt [Member], USD $)	Dec. 31, 2014
Long-term Debt [Member]
Debt Instrument [Line Items]
Principal payments on long term debt during next 5 years	$0

Shareholders_equity_Details

Shareholders' equity (Details) (USD $)	12 Months Ended	41 Months Ended	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Aug. 01, 2011	Jul. 31, 2008
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of common stock (in shares)		4,786,521
Common stock, shares authorized (in shares)		195,000,000	195,000,000	195,000,000
Stock repurchase program, authorized amount					$60,000
Treasury stock acquired, Aggregate purchase price	4,033	49,924
Stock repurchase program, Remaining authorized repurchase amount		$10,076	10,076
Series A Preferred stock, shares authorized (in shares)		5,000,000	5,000,000	5,000,000
Series A Preferred stock, shares issued (in shares)		160,000	160,000	160,000		160,000
Preferred Stock, Par or Stated Value Per Share		$0.01	0.01	0.01
Preferred Stock, Liquidation Preference Per Share		$0.01	0.01
Conversion of convertible preferred stock (in shares)		100	100
Series A Convertible Preferred Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, Beginning balance	80,718		79,620	80,283
Repurchase of common stock (in shares)	0
Conversion of convertible preferred stock (in shares)	-435		-1,479	-663
Issuance for share-based compensation plans (in shares)	0		0	0
Shares, Ending balance	80,283	78,141	78,141	79,620
Treasury stock, at cost [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, Beginning balance	4,386,521		4,786,521	4,786,521
Repurchase of common stock (in shares)	400,000
Conversion of convertible preferred stock (in shares)	0		0	0
Issuance for share-based compensation plans (in shares)	0		0	0
Shares, Ending balance	4,786,521	4,786,521	4,786,521	4,786,521
Common stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, Beginning balance	88,844,327		88,710,277	88,548,637
Repurchase of common stock (in shares)	-400,000
Conversion of convertible preferred stock (in shares)	43,556		147,952	66,244
Issuance for share-based compensation plans (in shares)	60,754		206,353	95,396
Shares, Ending balance	88,548,637	89,064,582	89,064,582	88,710,277

Inventories_Details

Inventories (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Thousands, unless otherwise specified
Inventory, Net [Abstract]
Raw materials	$78,599		$69,776
Work-in-process	33,941		22,183
Finished goods	19,969		17,661
Operating and other supplies	150,971		129,995
Inventories (1)	$283,480	[1]	$239,615	[1]
[1]	Includes inventory acquired in connection with the Mt. Holly acquisition. See Note 2 Business acquisitions for additional information about the Mt. Holly acquisition.

Property_Plant_and_Equipment_P

Property, Plant, and Equipment Property, Plant, and Equipment (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Property, Plant and Equipment [Abstract]
Land and improvements	$51,748	$16,021
Buildings and improvements	403,784	340,609
Machinery and equipment	1,395,221	1,464,532
Construction in progress	182,393	221,101
Property, plant and equipment, gross	2,033,146	2,042,263
Less accumulated depreciation	-741,928	-794,602
Property, plant and equipment - net	$1,291,218	$1,247,661

Property_Plant_and_Equipment_P1

Property, Plant, and Equipment Property, Plant, and Equipment (Detail Textual) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Property, plant and equipment — net	$1,291,218	$1,247,661
Construction in progress	182,393	221,101
Depreciation	70,731	66,570	62,570
Mt. Holly Property, plant and equipment, gross		179,702
Mt. Holly Property Property, plant and equipment, accumulated depreciation		119,275
Ravenswood Aluminum Smelter [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment — net	45,683
Helguvik Project [Member]
Property, Plant and Equipment [Line Items]
Construction in progress	$147,587

Supplemental_financial_stateme2

Supplemental financial statement info Components of Prepaid and Other Current Assets (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Prepaid and other assets	$19,601	$15,051
Income/withholding tax receivable – current	5,389	11,437
VAT receivable	4,778	5,648
Derivative assets	0	140
Total Prepaid and other current assets	$29,768	$32,276

Supplemental_financial_stateme3

Supplemental financial statement info Components of Other Assets (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Investment in BHH and other equity investments	$34,478	$35,767
Pension asset related to Mt. Holly	30,842	0
Cash surrender value of life insurance and trust assets	26,636	27,857
Maintenance and operating supplies – non-current	17,771	17,827
Other assets	13,850	10,023
Total Other assets	$123,577	$91,474

Supplemental_financial_stateme4

Supplemental financial statement info Components of Accrued and Other Current Liabilities (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Accrued payable to Alcoa for Mt. Holly acquisition	$39,208	$0
Accrued compensation and related benefits	19,602	11,829
Income taxes payable	14,302	6,198
Other accrued and current liabilities	10,573	14,842
Accrued vacation pay	9,101	9,135
Asset retirement obligations – current	6,006	4,230
Deferred tax liability – current	2,241	1,555
Accrued severance pay	2,050	11,438
Accrued bond interest	1,563	1,636
Revolving credit facility	0	6,000
Current portion of long-term debt	0	2,603
Total Accrued and other current liabilities	$104,646	$69,466

Supplemental_financial_stateme5

Supplemental financial statement info Components of Other Liabilities (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Asset retirement obligations – non-current	$30,944	$22,884
Other liabilities	9,275	7,576
Contingent consideration	5,837	0
Accrued workers’ compensation cost – non-current	7,216	7,283
E.ON contingent liability and accrued interest	0	0
Total Other liabilities	$53,272	$37,743

Supplemental_financial_stateme6

Supplemental financial statement info Components of Accumulated Other Comprehensive Loss (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	($129,913)		($105,891)
Income tax effect (2)	12,231	[1]	14,059	[1]
Accumulated other comprehensive loss	-117,682		-91,832		-151,192	-134,588
Defined benefit plan liabilities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	-128,664		-92,177
Income tax effect (2)	12,812		14,256
Accumulated other comprehensive loss	-115,852		-77,921		-137,441	-124,948
Equity in investee other comprehensive income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	0	[2]	-12,650	[2]
Income tax effect (2)	0		418
Accumulated other comprehensive loss	0		-12,232		-12,224	-7,918
Unrealized loss on financial instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	-1,249		-1,064
Income tax effect (2)	-581		-615
Accumulated other comprehensive loss	($1,830)		($1,679)		($1,527)	($1,722)
[1]	The allocation of the income tax effect to the components of other comprehensive income is as follows: 20142013Defined benefit plan liabilities$12,812$14,256Equity in investee other comprehensive income—418Unrealized loss on financial instruments(581)(615)
[2]	The amount includes our equity in the other comprehensive income of Mt. Holly until it was acquired.

Changes_in_components_of_Accum

Changes in components of Accumulated other comprehensive loss (Details) (USD $)	3 Months Ended																12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, Accumulated Other Comprehensive Loss	($117,682)								($91,832)								($117,682)	($91,832)	($151,192)	($134,588)
Other comprehensive income (loss) before reclassifications																	-43,345	56,787	-21,215
Net amount reclassified to net income (loss)																	4,844	2,573	4,611
Elimination of equity in investee resulting from acquisition																	12,651
Cost of goods sold																	1,728,586	1,414,790	1,225,769
Selling, general and administrative expenses																	49,195	67,477	35,363
Income tax expense																	18,308	3,131	8,910
Net income (loss)	61,849	[1]	50,405	[2]	20,344	[3]	-20,104	[4]	-9,675	[5]	-9,507	[6]	-29,384	[7]	8,253	[8]	112,494	-40,313	-35,610
Defined benefit plan liabilities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, Accumulated Other Comprehensive Loss	-115,852								-77,921								-115,852	-77,921	-137,441	-124,948
Other comprehensive income (loss) before reclassifications																	-42,926	56,795	-16,691
Net amount reclassified to net income (loss)																	4,995	2,725	4,198
Elimination of equity in investee resulting from acquisition																	0
Equity in investee other comprehensive income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, Accumulated Other Comprehensive Loss	0								-12,232								0	-12,232	-12,224	-7,918
Other comprehensive income (loss) before reclassifications																	-419	-8	-4,306
Net amount reclassified to net income (loss)																	0	0	0
Elimination of equity in investee resulting from acquisition																	12,651
Unrealized loss on financial instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, Accumulated Other Comprehensive Loss	-1,830								-1,679								-1,830	-1,679	-1,527	-1,722
Other comprehensive income (loss) before reclassifications																	0	0	-218
Net amount reclassified to net income (loss)																	-151	-152	413
Elimination of equity in investee resulting from acquisition																	0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Defined benefit plan liabilities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of goods sold																	6,237	3,264	4,670
Selling, general and administrative expenses																	569	990	1,055
Income tax expense																	-1,811	-1,529	-1,527
Net income (loss)																	4,995	2,725	4,198
Reclassification out of Accumulated Other Comprehensive Income [Member] | Equity in investee other comprehensive income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of goods sold																	0	0	0
Income tax expense																	-419	-70	-70
Net income (loss)																	-419	-70	-70
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized loss on financial instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of goods sold																	-185	-186	381
Income tax expense																	34	34	32
Net income (loss)																	($151)	($152)	$413
[1]	The fourth quarter of 2014 net income included a benefit of $7,943 for the gain on remeasurement of contingent consideration and a benefit of $1,318 for gain on remeasurement of our equity investment in Mt. Holly. Results were negatively impacted by $4,964 in non-cash, non-recurring pension charges and by $2,616 related to the separation of former senior executives.
[2]	The third quarter of 2014 net income reflects higher aluminum prices and lower power prices in the Midwestern U.S.
[3]	The second quarter of 2014 net income reflects higher aluminum prices and lower power prices in the Midwestern U.S. Results were negatively impacted by a charge of $500 for the finalization of a legal settlement.
[4]	The first quarter of 2014 cost of sales included a benefit of $5,534 related to deferred power contract liability amortization. Results were negatively impacted by a $3,100 charge for increased legal reserves.
[5]	The fourth quarter of 2013 cost of sales included a benefit of $16,570 related to deferred power contract liability amortization. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a credit of $9,040. The financial results also include an $8,400 charge relating to the separation of our former CEO.
[6]	The third quarter of 2013 cost of sales included an $11,720 benefit for deferred power contract liability amortization. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a credit of $5,762.
[7]	The second quarter of 2013 amounts differ from our reported second quarter results due to purchase price accounting adjustments related to the Sebree acquisition which were retroactively applied to the second quarter of 2013. The second quarter of 2013 net loss included a gain on bargain purchase of $5,253 and power contract amortization of $2,741 associated with the Sebree acquisition. Results were negatively impacted by a charge of $3,272 for the early extinguishment of our 8.0% Notes and a charge for severance and other expenses of $1,750 related to our corporate headquarters relocation. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a charge of $10,211.
[8]	The first quarter of 2013 net income included a net benefit of $2,225 related to a litigation reserve adjustment and an unrealized gain of $15,722 related to a LME-based contingent obligation. Results were negatively impacted by severance and other expenses of $2,213 related to our corporate headquarters relocation. The net effect of reporting inventory on a lower of cost or market basis was a charge to cost of goods sold of $5,838 in the quarter.

Pension_and_Other_Postretireme2

Pension and Other Postretirement Benefits Pension Benefits (Details) (Defined Benefit Pension Plans [Member], USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Pension Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Projected benefit obligation change due to curtailments	$6,600
Curtailment cost	263	-18	0
Settlements	4,701	0	0
Projected benefit obligation change due to settlements	$19,573	$0

Pension_and_Other_Postretireme3

Pension and Other Postretirement Benefits Employer contributions (Details) (USD $)	12 Months Ended		45 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2016
Defined Benefit Pension Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Employer contributions	$5,584	$11,130
PBGC Agreement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Pension Contributions		6,700
Pension Contributions Above Required Minimum, Current Year Scheduled Amount	3,700
Scenario, Forecast [Member] | PBGC Agreement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Pension Contributions Above Required Minimum, Total			17,400
Pension Contributions Above Required Minimum, Remaining			$10,700

Pension_and_Other_Postretireme4

Pension and Other Postretirement Benefits Change in benefit obligation (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Change in benefit obligation [Roll Forward]
Benefit obligation at end of year	$336,292	$238,319
Defined Benefit Pension Plans [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year	238,319	174,954
Service cost	5,605	4,735	2,802
Interest cost	11,629	8,908	6,871
Plan amendments	-5,308	0
Medicare Part D	0	0
Actuarial loss (gain)	32,772	-21,539
Acquisition	84,743	82,988
Benefits paid	-11,895	-11,727
Settlements	-19,573	0
Benefit obligation at end of year	336,292	238,319	174,954
Other Postretirement Benefit Plans [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year	134,652	149,263
Service cost	1,591	2,527	1,790
Interest cost	6,420	5,681	5,512
Plan amendments	0	0
Medicare Part D	273	0
Actuarial loss (gain)	17,669	-24,170
Acquisition	2,857	6,544
Benefits paid	-4,681	-5,193
Settlements	0	0
Benefit obligation at end of year	$158,781	$134,652	$149,263

Pension_and_Other_Postretireme5

Pension and Other Postretirement Benefits Change in Plan Assets (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Change in fair value of plan assets [Roll Forward]
Fair value of assets at end of year	$305,520	$199,304
Defined Benefit Pension Plans [Member]
Change in fair value of plan assets [Roll Forward]
Fair value of plan assets at beginning of year	199,304	96,234
Actual return on plan assets	16,118	21,675
Acquisition	115,982	81,992
Employer contributions	5,584	11,130
Benefits paid	-11,895	-11,727
Settlements	-19,573	0
Fair value of assets at end of year	305,520	199,304
Other Postretirement Benefit Plans [Member]
Change in fair value of plan assets [Roll Forward]
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Acquisition	0	0
Employer contributions	4,681	5,193
Benefits paid	-4,681	-5,193
Settlements	0	0
Fair value of assets at end of year	$0	$0

Pension_and_Other_Postretireme6

Pension and Other Postretirement Benefits Funded status of plans (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Current liabilities	($10,159)	($8,410)
Defined Benefit Pension Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Funded status	-30,772	-39,015
Non-current assets	30,842	2,547
Current liabilities	-1,744	-1,714
Non-current liabilities	-59,870	-39,848
Net amount recognized	-30,772	-39,015
Net loss	63,360	45,642
Prior service cost (benefit)	1,335	376
Total recognized in accumulated other comprehensive loss (pre-tax)	64,695	46,018
Other Postretirement Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Funded status	-158,781	-134,652
Non-current assets	0	0
Current liabilities	-6,118	-5,368
Non-current liabilities	-152,663	-129,284
Net amount recognized	-158,781	-134,652
Net loss	79,720	65,754
Prior service cost (benefit)	-15,751	-19,595
Total recognized in accumulated other comprehensive loss (pre-tax)	$63,969	$46,159

Pension_and_Other_Postretireme7

Pension and Other Postretirement Benefits PBO, ABO, FV of Plan Assets (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Projected Benefit Obligation	$336,292	$238,319
Accumulated Benefit Obligation	328,963	231,460
Fair Value of Plan assets	305,520	199,304
Sebree Hourly Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Projected Benefit Obligation	90,320	80,369
Accumulated Benefit Obligation	90,320	80,369
Fair Value of Plan assets	84,432	82,916
CAWV Hourly Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Projected Benefit Obligation	61,989	66,866
Accumulated Benefit Obligation	61,989	66,852
Fair Value of Plan assets	55,273	64,905
Salaried pension plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Projected Benefit Obligation	71,017	66,686
Accumulated Benefit Obligation	68,247	60,870
Fair Value of Plan assets	49,367	51,483
CASC pension plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Projected Benefit Obligation	85,605	0
Accumulated Benefit Obligation	82,556	0
Fair Value of Plan assets	116,448	0
SERB plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Projected Benefit Obligation	27,361	24,398
Accumulated Benefit Obligation	25,851	23,369
Fair Value of Plan assets	$0	$0

Pension_and_Other_Postretireme8

Pension and Other Postretirement Benefits Net Periodic Benefit Cost (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Pension Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service cost	$5,605	$4,735	$2,802
Interest cost	11,629	8,908	6,871
Expected return on plan assets	-14,694	-10,592	-6,962
Amortization of prior service costs	77	113	137
Amortization of net loss	1,907	3,152	3,642
Net periodic benefit cost	4,524	6,316	6,490
Settlements	4,701	0	0
Curtailment cost	263	-18	0
Total net periodic benefit cost	9,488	6,298	6,490
Other Postretirement Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service cost	1,591	2,527	1,790
Interest cost	6,420	5,681	5,512
Expected return on plan assets	0	0	0
Amortization of prior service costs	-3,844	-3,995	-4,250
Amortization of net loss	3,704	5,022	6,195
Net periodic benefit cost	7,871	9,235	9,247
Settlements	0	0	0
Curtailment cost	0	-20	0
Total net periodic benefit cost	$7,871	$9,215	$9,247

Pension_and_Other_Postretireme9

Pension and Other Postretirement Benefits Changes in Plan Assets & Benefit Obligation Recognized in OCI (pre-taxed) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net loss (gain)	$41,995	($56,795)	$16,691
Prior service cost (benefit)	1,299	0	0
Amortization of prior service benefit (cost), including recognition due to curtailment	3,504	3,920	4,113
Defined Benefit Pension Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net loss (gain)	24,326	-32,624
Prior service cost (benefit)	1,299	0
Amortization of net loss, including recognition due to settlement	-6,608	-3,152
Amortization of prior service benefit (cost), including recognition due to curtailment	-340	-95
Total amount recognized in other comprehensive loss	18,677	-35,871
Net periodic benefit cost	9,488	6,298	6,490
Total recognized in net periodic benefit cost and other comprehensive loss	28,165	-29,573
Other Postretirement Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net loss (gain)	17,669	-24,171
Prior service cost (benefit)	0	0
Amortization of net loss, including recognition due to settlement	-3,704	-5,022
Amortization of prior service benefit (cost), including recognition due to curtailment	3,844	4,015
Total amount recognized in other comprehensive loss	17,809	-25,178
Net periodic benefit cost	7,871	9,215	9,247
Total recognized in net periodic benefit cost and other comprehensive loss	$25,680	($15,963)

Recovered_Sheet3

Pension and Other Postretirement Benefits Amoritized from AOCI during the next fiscal year (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Defined Benefit Pension Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Amortization of net loss	$3,601
Amortization of prior service cost (benefit)	99
Other Postretirement Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Amortization of net loss	4,712
Amortization of prior service cost (benefit)	($3,845)

Recovered_Sheet4

Pension and Other Postretirement Benefits Weighted Average assumptions used in calculating benefit obligations (Details)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Defined Benefit Pension Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Discount rate	4.05%		4.89%
Rate of compensation increase, first four years	3.00%	[1]	3.00%	[1]
Rate of compensation increase, year five and thereafter	4.00%	[1]	4.00%	[1]
Measurement date	12/31/14		12/31/13
Other Postretirement Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Discount rate	4.00%		4.99%
Rate of compensation increase, first four years	3.00%	[1]	3.00%	[1]
Rate of compensation increase, year five and thereafter	4.00%	[1]	4.00%	[1]
Measurement date	12/31/14		12/31/13
[1]	The rate of compensation increase is 3% per year for first four years and 4% per year for year five and thereafter.

Recovered_Sheet5

Pension and Other Postretirement Benefits Discount Rate Change in Estimate (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Basis point change to discount rate (in basis points)	25
Pension Obligation due to change in discount rate	$10,000

Recovered_Sheet6

Pension and Other Postretirement Benefits Weighted average assumptions used to determine net periodic benefit cost (Details)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Defined Benefit Pension Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Measurement date	12/31/13		12/31/12		12/31/11
Fiscal year end	12/31/14		12/31/13		12/31/12
Discount rate	4.89%		4.00%		4.25%
Rate of compensation increase, group 1	3.00%	[1]	3.00%	[1]	3.00%	[1]
Rate of compensation increase, group 2	4.00%	[1]	4.00%	[1]	4.00%	[1]
Expected return on plan assets	7.25%		7.25%		8.00%
Other Postretirement Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Measurement date	12/31/13		12/31/12		12/31/11
Fiscal year end	12/31/14		12/31/13		12/31/12
Discount rate	4.99%		4.01%		3.83%
Rate of compensation increase, group 1	3.00%	[1]	3.00%	[1]	3.00%	[1]
Rate of compensation increase, group 2	4.00%	[1]	4.00%	[1]	4.00%	[1]
Expected return on plan assets	0.00%		0.00%		0.00%
[1]	For 2014, the rate of compensation increase is 3% per year for first four years and 4% per year for year five and thereafter. For 2013 and 2012, the rate of compensation increase is 3% per year for first five years and 4% per year for year six and thereafter.

Recovered_Sheet7

Pension and Other Postretirement Benefits Assumed health care trend rates (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Medical cost inflation rate (in hundredths)	8.00%
Medical cost inflation, years 7 and thereafter (in hundredths)	5.00%
Effect of One Percentage Point Increase on Service and Interest Cost Components	$1,258
Effect of One Percentage Point Decrease on Service and Interest Cost Components	-1,019
Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation	24,815
Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation	($20,140)

Recovered_Sheet8

Pension and Other Postretirement Benefits Company matching contribution to defined contribution 401(K) plans (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Contribution Plan Disclosure [Line Items]
Company matching contribution to defined contribution (401(k)) plans	$1,547	$1,138	$748

Recovered_Sheet9

Pension and Other Postretirement Benefits Pension Plan Asset Allocation (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012	Dec. 01, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Actual Plan Asset Allocations	100.00%		100.00%
Fair Value of Plan assets	$305,520		$199,304
U.S. Equities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Target Allocation Percentage Of Assets	50.00%
Actual Plan Asset Allocations	42.00%		43.00%
Fair Value of Plan assets	79,148		86,323
International Equities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Target Allocation Percentage Of Assets	15.00%
Actual Plan Asset Allocations	18.00%		20.00%
Fair Value of Plan assets	33,720		40,093
Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Target Allocation Percentage Of Assets	35.00%
Actual Plan Asset Allocations	40.00%		37.00%
Fair Value of Plan assets	76,204		72,888
Plan receivable [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair Value of Plan assets	116,448	[1]
Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair Value of Plan assets	189,072		199,304
Fair Value, Inputs, Level 1 [Member] | U.S. Equities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair Value of Plan assets	79,148		86,323
Fair Value, Inputs, Level 1 [Member] | International Equities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair Value of Plan assets	33,720		40,093
Fair Value, Inputs, Level 1 [Member] | Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair Value of Plan assets	76,204		72,888
Fair Value, Inputs, Level 1 [Member] | Plan receivable [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair Value of Plan assets	0	[1]
Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair Value of Plan assets	0		0
Fair Value, Inputs, Level 2 [Member] | U.S. Equities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair Value of Plan assets	0		0
Fair Value, Inputs, Level 2 [Member] | International Equities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair Value of Plan assets	0		0
Fair Value, Inputs, Level 2 [Member] | Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair Value of Plan assets	0		0
Fair Value, Inputs, Level 2 [Member] | Plan receivable [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair Value of Plan assets	0	[1]
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair Value of Plan assets	116,448		0
Fair Value, Inputs, Level 3 [Member] | U.S. Equities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair Value of Plan assets	0		0
Fair Value, Inputs, Level 3 [Member] | International Equities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair Value of Plan assets	0		0
Fair Value, Inputs, Level 3 [Member] | Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair Value of Plan assets	0		0
Fair Value, Inputs, Level 3 [Member] | Plan receivable [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair Value of Plan assets	116,448	[1]
Defined Benefit Pension Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Expected return on plan assets	7.25%		7.25%	8.00%
Fair Value of Plan assets	$305,520		$199,304	$96,234
Mt. Holly Smelter [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Percentage of voting interests acquired (percentage)					50.30%
[1]	Represents the receivable to the Century Aluminum of South Carolina defined benefit plan related to pension funding obligations under the Stock Purchase Agreement. Amount is subject to final approval by the parties which is expected in the second quarter of 2015.

Recovered_Sheet10

Pension and Other Postretirement Benefits Expected Contribution Cash Flows (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Defined Benefit Pension Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	$5,306
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	17,487
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	17,965
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	18,191
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	19,958
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	19,830
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	97,247
Other Postretirement Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	6,118
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	6,118
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	6,605
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	7,212
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	7,691
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	8,216
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	$43,357

Recovered_Sheet11

Pension and Other Postretirement Benefits Participation in Multi-Employer Pension Plans (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Multiemployer Plans [Line Items]
EIN / PN	23-6648508/499
Pension Protection Act Zone Status	Green	[1]	Green	[1]
Subject to Financial Improvement/Rehabilitation Plan	No
Contributions of Century Aluminum Company	$2,164		$2,171		$2,282
Withdrawal from Plan Probable	No
Surcharge Imposed	No
Expiration Date of Collective Bargaining Agreement	1-Apr-15
Funded status of Green zone	At least 80 percent
[1]	The most recent Pension Protection Act zone status available in 2014 and 2013 is for the plan's year-end December 31, 2013 and December 31, 2012, respectively. The zone status is based on information that Century received from the plan as well as publicly available information per the Department of Labor and is certified by the plan’s actuary. Among other factors, plans in the green zone are at least 80 percent funded.

Share_Based_Compensation_Share

Share Based Compensation Share Based Compensation (Details) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options to purchase common stock (in Shares)		619,833
Service-Based Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service-based share awards outstanding (in Shares)	464,485	442,737
Amended and Restated Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Incentive Plan, shares authorized (in Shares)	10,000,000
Stock Incentive Plan, shares remaining (in Shares)	6,900,000
Stock Incentive Plan, expected term (years)	10 years
Share based compensation, vesting rights (in time period)	3 years
Options to purchase common stock (in Shares)	544,171
Amended and Restated Stock Option Plan [Member] | Non-employee director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, vesting rights (in time period)	12 months
Amended and Restated Stock Option Plan [Member] | Grant date [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Incentive Plan, vesting rights	one-third
Amended and Restated Stock Option Plan [Member] | Anniversary date [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Incentive Plan, vesting rights	one-third
Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, vesting rights (in time period)	3 years
Performance unit liability	6,251

Share_Based_Compensation_Servi

Share Based Compensation Service-Based Awards - Options (Details) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Options outstanding (in Shares)			619,833
Options outstanding, Weighted Average Exercise Price (in dollars per share)			$24.77
Options exercised (in Shares)	-61,495
Options exercised, Weighted Average Exercise Price (in dollars per share)	$6.55
Options forfeited/expired (in Shares)	-14,167
Options forfeited/expired, Weighted Average Exercise Price (in dollars per share)	$23.76
Outstanding, fully vested and exercisable (in Shares)	544,171	[1]
Outstanding, fully vested and exercisable, Weighted Average Exercise Price (in dollars per share)	$26.85	[1]
Outstanding, fully vested and exercisable, Weighted Average Remaining Contractual Term (years)	2 years 9 months 10 days	[1]
Outstanding, fully vested and exercisable, Aggregate Intrinsic Value	$3,794	[1]
[1]	As the result of actions in 2011 that were determined to be a "change of control" under the Stock Incentive Plan, all options will remain exercisable for their respective remaining term, regardless of whether the awardees remain employees of Century.

Share_Based_Compensation_Servi1

Share Based Compensation Service Based Awards Rollforward (Details) (Service-Based Share Awards [Member])	12 Months Ended
	Dec. 31, 2014
Service-Based Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service-based share awards outstanding, beginning of period (in Shares)	442,737
Granted (in Shares)	258,662
Vested (in Shares)	-200,965
Forfeited (in Shares)	-35,949
Service-based share awards outstanding, end of period (in Shares)	464,485

Share_Based_Compensation_Servi2

Share Based Compensation Service-Based Awards, Additional disclosures (Details) (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Service-Based Awards, Additional disclosures [Abstract]
Weighted average per share fair value of service-based share grants (in dollars per share)	$15.31	$8.19	$8.14
Total intrinsic value of option exercises	$1,011	$13	$0

Share_Based_Compensation_Share1

Share Based Compensation Share and performance-based compensation expense (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share and performance-based compensation expense [Abstract]
Performance-based share expense	$1,090	$475	$27
Service-based share expense	244	603	586
Stock option expense	0	0	0
Total share-based compensation expense before income tax	1,334	1,078	613
Income tax	0	0	0
Total share-based compensation expense, net of income tax	1,334	1,078	613
Unrecognized compensation expense	$1,826
Weighted average period of expense recognition (in time period)	1 year

Earnings_per_share_Details

Earnings per share (Details) (USD $)

3 Months Ended

12 Months Ended

In Thousands, except Per Share data, unless otherwise specified

Dec. 31, 2014

Sep. 30, 2014

Jun. 30, 2014

Mar. 31, 2014

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Earnings Per Share [Abstract]

Net income (loss)

$61,849

[1]

$50,405

[2]

$20,344

[3]

($20,104)

[4]

($9,675)

[5]

($9,507)

[6]

($29,384)

[7]

$8,253

[8]

$112,494

($40,313)

($35,610)

Amount allocated to common shareholders (in hundredths)

91.81%

100.00%

[9]

100.00%

[9]

Basic EPS:

Net income (loss) allocated to common stockholders

56,824

[1]

46,277

[2]

18,675

[3]

-20,104

[4]

-9,675

[5]

-9,507

[6]

-29,384

[7]

7,567

[8]

103,283

Weighted Average Number of Shares Outstanding, in Shares (000)

88,823

Earnings Per Share, Basic (in dollars per share)

$0.64

[1]

$0.52

[2]

$0.21

[3]

($0.23)

[4]

($0.11)

[5]

($0.11)

[6]

($0.33)

[7]

$0.09

[8]

$1.16

($0.45)

($0.40)

Basic and Diluted EPS:

Net income (loss) allocated to common stockholders

-40,313

-35,610

Weighted Average Number of Shares Outstanding, in Shares (000)

88,612

88,534

Earnings Per Share, Basic and Diluted (in dollars per share)

($0.45)

($0.40)

Effect of Dilutive Securities:

Share-based stock awards - in Shares (000)

605

Diluted EPS:

Net income (loss) allocated to common stockholders with assumed conversion

$103,283

Income (loss) applicable to common shareholders with assumed conversion - in Shares (000)

89,428

Earnings Per Share, Diluted (in dollars per share)

$0.63

[1]

$0.52

[2]

$0.21

[3]

($0.23)

[4]

($0.11)

[5]

($0.11)

[6]

($0.33)

[7]

$0.09

[8]

$1.15

($0.45)

($0.40)

[1]

The fourth quarter of 2014 net income included a benefit of $7,943 for the gain on remeasurement of contingent consideration and a benefit of $1,318 for gain on remeasurement of our equity investment in Mt. Holly. Results were negatively impacted by $4,964 in non-cash, non-recurring pension charges and by $2,616 related to the separation of former senior executives.

[2]

The third quarter of 2014 net income reflects higher aluminum prices and lower power prices in the Midwestern U.S.

[3]

The second quarter of 2014 net income reflects higher aluminum prices and lower power prices in the Midwestern U.S. Results were negatively impacted by a charge of $500 for the finalization of a legal settlement.

[4]

The first quarter of 2014 cost of sales included a benefit of $5,534 related to deferred power contract liability amortization. Results were negatively impacted by a $3,100 charge for increased legal reserves.

[5]

The fourth quarter of 2013 cost of sales included a benefit of $16,570 related to deferred power contract liability amortization. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a credit of $9,040. The financial results also include an $8,400 charge relating to the separation of our former CEO.

[6]

The third quarter of 2013 cost of sales included an $11,720 benefit for deferred power contract liability amortization. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a credit of $5,762.

[7]

The second quarter of 2013 amounts differ from our reported second quarter results due to purchase price accounting adjustments related to the Sebree acquisition which were retroactively applied to the second quarter of 2013. The second quarter of 2013 net loss included a gain on bargain purchase of $5,253 and power contract amortization of $2,741 associated with the Sebree acquisition. Results were negatively impacted by a charge of $3,272 for the early extinguishment of our 8.0% Notes and a charge for severance and other expenses of $1,750 related to our corporate headquarters relocation. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a charge of $10,211.

[8]

The first quarter of 2013 net income included a net benefit of $2,225 related to a litigation reserve adjustment and an unrealized gain of $15,722 related to a LME-based contingent obligation. Results were negatively impacted by severance and other expenses of $2,213 related to our corporate headquarters relocation. The net effect of reporting inventory on a lower of cost or market basis was a charge to cost of goods sold of $5,838 in the quarter.

[9]

We have not allocated net losses between common and preferred stockholders, as the holders of our preferred shares do not have a contractual obligation to share in the loss.

Earnings_per_share_Antidilutiv

Earnings per share Antidilutive securities excluded from the calculation of diluted EPS (Details)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	320,553	[1]	619,833	[1]	626,334	[1]
Service-Based Share Awards [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	[1]	442,737	[1]	396,133	[1]
[1]	In periods when we report a net loss, all share awards are excluded from the calculation of diluted weighted average shares outstanding because of their antidilutive effect on earnings (loss) per share.

Income_taxes_Details

Income taxes (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
U.S.	$77,046	($47,080)	($38,762)
Foreign	52,451	7,236	9,439
Income (loss) before income taxes and equity in earnings of joint ventures	$129,497	($39,844)	($29,323)

Income_taxes_Significant_compo

Income taxes Significant components of Income tax expense (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract]
U.S. federal current expense (benefit)	($112)	$532	($161)
State current expense (benefit)	2,252	-445	-669
Foreign current expense	15,098	6,198	9,808
Total current expense	17,238	6,285	8,978
U.S. federal deferred benefit	-1,696	-3,905	-1,564
State deferred benefit	-12	-207	0
Foreign deferred tax expense	2,778	958	1,496
Total deferred benefit	1,070	-3,154	-68
Total income tax expense	$18,308	$3,131	$8,910

Income_taxes_Reconciliation_of

Income taxes Reconciliation of statutory to effective income tax rate (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal Statutory Rate	35.00%	35.00%	35.00%
Permanent differences	4.30%	54.50%	12.60%
State taxes, net of Federal benefit	-6.30%	97.20%	0.10%
Foreign earnings taxed at different rates than U.S.	-0.50%	17.40%	-369.50%
Valuation allowance	-25.40%	-265.90%	297.60%
Changes in uncertain tax reserves	0.60%	40.50%	-6.70%
Other	6.40%	13.40%	0.50%
Effective tax rate	14.10%	-7.90%	-30.40%

Recovered_Sheet12

Income taxes Significant Components of our deferred tax assets & liabilities (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Accrued postretirement benefit cost	$15,683	$12,851
Accrued liabilities	4,494	2,355
Share-based compensation	7,350	5,327
Derivative and hedging contracts	58,687	116,550
Goodwill	10,521	12,421
Equity contra - other comprehensive loss	81,567	61,216
Dual consolidated losses and capital losses	7,509	14,512
Net operating losses and tax credits	646,158	637,721
Foreign basis differences	668	0
Other	1,239	1,533
Total deferred tax assets	833,876	864,486
Valuation allowance	-748,283	-765,023
Net deferred tax assets	85,593	99,463
Tax over financial statement depreciation	-142,627	-145,945
Pension	-14,222	-11,543
Unremitted foreign earnings	-30,308	-35,344
Foreign basis differences	0	-790
Total deferred tax liabilities	-187,157	-193,622
Net deferred tax liability	($101,564)	($94,159)

Income_taxes_Changes_in_Valuat

Income taxes Changes in Valuation Allowance (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Valuation Allowance [Line Items]
Balance, valuation allowance	$765,023	$656,352
Change in valuation allowance	-16,740	108,671
Balance, valuation allowance	$748,283	$765,023

Income_taxes_Significant_Compo1

Income taxes Significant Components of our Deferred Tax Assets & Liabilities - Additional Info (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Components of Deferred Tax Assets and Liabilities [Abstract]
Net operating losses that will increase equity if and when such deferred tax assets are realized	$7,499

Income_taxes_Net_Operating_Los

Income taxes Net Operating Losses Carryforwards (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Federal [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Dates	31-Dec-28
Operating Loss Carryforwards	$1,306,482	[1]	$1,287,118	[1]
State [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Dates	31-Dec-27
Operating Loss Carryforwards	2,078,105	[2]	2,077,890	[2]
Foreign [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$446,234	[3]	$459,457	[3]
Iceland [Member] | Foreign [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Dates	31-Dec-17
Netherlands [Member] | Foreign [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Dates	31-Dec-22
[1]	The federal NOL begins to expire in 2028.
[2]	The state NOLs begin to expire in 2027.
[3]	The Icelandic NOL begins to expire in 2017; Dutch NOL begins to expire in 2022.

Income_taxes_Gross_Unrecognize

Income taxes Gross Unrecognized Tax Benefits (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Balance as of January 1,	$1,200	$17,600	$15,900
Additions based on tax positions related to the current year	1,100	700	2,700
Decreases due to lapse of applicable statute of limitations	-300	-2,800	-800
Settlements	0	-14,300	-200
Balance as of December 31,	$2,000	$1,200	$17,600

Income_taxes_Components_of_unr

Income taxes Components of unrecognized tax positions (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Highly certain tax positions	$1,900	$1,100	$16,900
Other unrecognized tax benefits	100	100	700
Gross unrecognized tax benefits	2,000	1,200	17,600	15,900
Accrued interest and penalties related to unrecognized tax benefits	$0	$100	$100

Income_taxes_Additional_income

Income taxes Additional income tax details (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2014
Income Tax Disclosure [Abstract]
Reduction in reserve for unrecognized tax benefits related to prior years	$14,300
Proceeds from income tax refunds	5,009
Federal [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$1,287,118	[1]	$1,306,482	[1]
[1]	The federal NOL begins to expire in 2028.

Commitments_and_contingencies_

Commitments and contingencies Environmental Contingencies (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Accrual for Environmental Loss Contingencies [Abstract]
Environmental-related accrued liabilities	$1,101	$999

Commitments_and_contingencies_1

Commitments and contingencies Matters relating to the St. Croix Alumina Refining Facility (Details) (USD $)	162 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Accrual for Environmental Loss Contingencies [Abstract]
Environmental remediation expense for Hydrocarbon Recovery Plan	$1,033

Commitments_and_contingencies_2

Commitments and contingencies Legal Contingencies (Details) (USD $)	12 Months Ended	45 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2016	Dec. 31, 2014
PBGC Agreement [Member]
Loss Contingencies [Line Items]
Pension Contributions	$6,700
Scenario, Forecast [Member] | PBGC Agreement [Member]
Loss Contingencies [Line Items]
Pension Contributions Above Required Minimum, Total		17,400
Grundartangi Power Agreement [Member]
Loss Contingencies [Line Items]
Litigation Settlement, Amount			$3,600

Commitments_and_contingencies_3

Commitments and contingencies (Details) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified	LaborUnions
	MW
OR Power Purchase Agreement Abstract]
Power currently available under the power purchase agreement (in megawatts)	47.5
Power prepayments	$2,062
Labor Commitments [Abstract]
Percentage of Company's work force represented by a union (in hundredths)	59.00%
Percentage of Grundartangi work force represented by the labor unions (in hundredths)	81.00%
Number of Labor Unions Under New Labor Agreement (in number of unions)	5
Percentage of Vlissingen work force represented by the labor union (in hundredths)	80.00%
Percentage of U.S. based work force represented by a union (in hundredths)	54.00%

Forward_delivery_contracts_and2

Forward delivery contracts and financial instruments (Details)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
	t		t
Long-Term Tolling Contracts [Member] | Glencore Toll Agreement 1 [Member]
Supply Commitment [Line Items]
Annual Primary Aluminum Physical Delivery Contract_Maximum	90,000
Customer	Glencore
Volume	90,000 tonnes per year ("tpy")
Term	Through July 2016
Pricing	Variable, based on LME and European Duty Paid premium
Primary Aluminum Sales Contracts [Member] | Glencore Nordural Metal Agreement [Member]
Supply Commitment [Line Items]
Annual Primary Aluminum Physical Delivery Contract_Maximum	205,000
Customer	Glencore	[1]
Volume	All primary aluminum produced at Grundartangi, net of tolling and other sales commitments	[1]
Term	January 1, 2014 through December 31, 2017	[1]
Pricing	Variable, based on LME and European Duty Paid premium and product premiums, as applicable	[1]
Other Forward Delivery Contracts [Member]
Supply Commitment [Line Items]
Other forward delivery contracts to sell primary aluminum (in tonnes)	6,108		118,373
Glencore [Member] | Other Forward Delivery Contracts [Member]
Supply Commitment [Line Items]
Other forward delivery contracts to sell primary aluminum (in tonnes)	4,058		20,008
[1]	The Glencore Grundartangi Metal Agreement is for all metal produced at Grundartangi from 2014 through 2017 less commitments under existing tolling and other sales contracts. Grundartangi currently estimates that it will sell Glencore approximately 205,000 tonnes of aluminum under this agreement in 2015.

Asset_retirement_obligations_A2

Asset retirement obligations (“ARO”) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Asset Retirement Obligation [Roll Forward]
Beginning balance, ARO liability	$27,113	$16,124
Additional ARO liability incurred	2,548	1,730
ARO liabilities settled	-4,731	-2,580
Accretion expense	1,517	1,733
Ending balance, ARO liability	36,950	27,113
Sebree Smelter [Member]
Asset Retirement Obligation [Roll Forward]
Additional ARO liability from acquisitions	0	10,106
Mt. Holly Smelter [Member]
Asset Retirement Obligation [Roll Forward]
Additional ARO liability from acquisitions	$10,503	$0

Supplemental_cash_flow_informa2

Supplemental cash flow information (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Interest	$19,066		$20,539		$20,212
Income/withholding taxes (1)	12,189	[1]	28,654	[1]	41,455	[1]
Accrued capital costs	744		9,409		-683
Iceland [Member]
Income/withholding taxes (1)	$5,491		$18,067		$22,633
[1]	We paid withholding taxes in Iceland on intercompany dividends of $5,491, $18,067 and $22,633 during the years ended December 31, 2014, 2013 and 2011, respectively. Our tax payments in Iceland for withholding taxes, income taxes and any associated refunds are denominated in ISK.

Quarterly_Information_Unaudite2

Quarterly Information (Unaudited) Financial Results by Quarter (Details) (USD $)	3 Months Ended																12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Data [Abstract]
Net sales	$551,239	[1]	$500,632	[2]	$458,324	[3]	$420,847	[4]	$401,174	[5]	$399,928	[6]	$331,937	[7]	$321,274	[8]	$1,931,042	$1,454,313	$1,272,111
Gross profit (loss)	89,996	[1]	75,714	[2]	38,504	[3]	-1,758	[4]	15,285	[5]	12,354	[6]	-5,698	[7]	17,582	[8]	202,456	39,523	46,342
Net income (loss)	61,849	[1]	50,405	[2]	20,344	[3]	-20,104	[4]	-9,675	[5]	-9,507	[6]	-29,384	[7]	8,253	[8]	112,494	-40,313	-35,610
Net income (loss) allocated to common stockholders	$56,824	[1]	$46,277	[2]	$18,675	[3]	($20,104)	[4]	($9,675)	[5]	($9,507)	[6]	($29,384)	[7]	$7,567	[8]	$103,283
Basic earnings (loss) per share (in dollars per share)	$0.64	[1]	$0.52	[2]	$0.21	[3]	($0.23)	[4]	($0.11)	[5]	($0.11)	[6]	($0.33)	[7]	$0.09	[8]	$1.16	($0.45)	($0.40)
Diluted earnings (loss) per share (in dollars per share)	$0.63	[1]	$0.52	[2]	$0.21	[3]	($0.23)	[4]	($0.11)	[5]	($0.11)	[6]	($0.33)	[7]	$0.09	[8]	$1.15	($0.45)	($0.40)
[1]	The fourth quarter of 2014 net income included a benefit of $7,943 for the gain on remeasurement of contingent consideration and a benefit of $1,318 for gain on remeasurement of our equity investment in Mt. Holly. Results were negatively impacted by $4,964 in non-cash, non-recurring pension charges and by $2,616 related to the separation of former senior executives.
[2]	The third quarter of 2014 net income reflects higher aluminum prices and lower power prices in the Midwestern U.S.
[3]	The second quarter of 2014 net income reflects higher aluminum prices and lower power prices in the Midwestern U.S. Results were negatively impacted by a charge of $500 for the finalization of a legal settlement.
[4]	The first quarter of 2014 cost of sales included a benefit of $5,534 related to deferred power contract liability amortization. Results were negatively impacted by a $3,100 charge for increased legal reserves.
[5]	The fourth quarter of 2013 cost of sales included a benefit of $16,570 related to deferred power contract liability amortization. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a credit of $9,040. The financial results also include an $8,400 charge relating to the separation of our former CEO.
[6]	The third quarter of 2013 cost of sales included an $11,720 benefit for deferred power contract liability amortization. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a credit of $5,762.
[7]	The second quarter of 2013 amounts differ from our reported second quarter results due to purchase price accounting adjustments related to the Sebree acquisition which were retroactively applied to the second quarter of 2013. The second quarter of 2013 net loss included a gain on bargain purchase of $5,253 and power contract amortization of $2,741 associated with the Sebree acquisition. Results were negatively impacted by a charge of $3,272 for the early extinguishment of our 8.0% Notes and a charge for severance and other expenses of $1,750 related to our corporate headquarters relocation. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a charge of $10,211.
[8]	The first quarter of 2013 net income included a net benefit of $2,225 related to a litigation reserve adjustment and an unrealized gain of $15,722 related to a LME-based contingent obligation. Results were negatively impacted by severance and other expenses of $2,213 related to our corporate headquarters relocation. The net effect of reporting inventory on a lower of cost or market basis was a charge to cost of goods sold of $5,838 in the quarter.

Quarterly_Information_Unaudite3

Quarterly Information (Unaudited) 2014 Financial Results Overview (Details) (USD $)	3 Months Ended							12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Data [Abstract]
Gain on fair value of contingent consideration	$7,943							$7,943	$0	$0
Gain on remeasurement of equity investment	1,318							1,318	0	0
Pension charges	4,964
Litigation settlement expense	2,616	500		8,400
Sebree power contract amortization			5,534	16,570	11,720	2,741		5,534	31,031	0
Increase (Decrease) in litigation reserve			$3,100				$2,225

Quarterly_Information_Unaudite4

Quarterly Information (Unaudited) 2013 Financial Results Overview (Details) (USD $)	3 Months Ended							12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Data [Abstract]
Sebree power contract amortization			$5,534	$16,570	$11,720	$2,741		$5,534	$31,031	$0
Lower of cost or market inventory adjustments				9,040	5,762	10,211	5,838		9,040
Litigation settlement expense	2,616	500		8,400
Loss on early extinguishment of debt						3,272		0	-3,272	0
Relocation expense						1,750	2,213
Increase (Decrease) in litigation reserve			3,100				2,225
Unrealized gain (loss) on E.ON obligation							15,722	1,412	16,781	0
Gain on bargain purchase						$5,253		$0	$5,253	$0

Business_Segments_Details

Business Segments (Details)	12 Months Ended
	Dec. 31, 2014
	segments
Segment Reporting [Abstract]
Number of Operating Segments	4
Number of Reportable Segments	1

Business_Segments_Segment_Asse

Business Segments Segment Assets (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
In Thousands, unless otherwise specified
Segment Reporting Information [Line Items]
Primary	$1,971,900	[1]	$1,770,749	[1]	$1,730,321	[1]
Corporate, unallocated	42,135	[1]	39,447	[1]	46,005	[1]
TOTAL	$2,014,035	[1]	$1,810,196	[1]	$1,776,326	[1]
[1]	Segment assets include accounts receivable, due from affiliates, prepaid and other current assets, inventory, intangible assets and property, plant and equipment — net; the remaining assets are unallocated corporate assets.

Business_Segments_Geography_Se

Business Segments Geography, Segment Reporting (Details) (USD $)

3 Months Ended

12 Months Ended

In Thousands, unless otherwise specified

Dec. 31, 2014

Sep. 30, 2014

Jun. 30, 2014

Mar. 31, 2014

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Revenues from External Customers and Long-Lived Assets [Line Items]

Net sales

$551,239

[1]

$500,632

[2]

$458,324

[3]

$420,847

[4]

$401,174

[5]

$399,928

[6]

$331,937

[7]

$321,274

[8]

$1,931,042

$1,454,313

$1,272,111

United States [Member]

Revenues from External Customers and Long-Lived Assets [Line Items]

Net sales

1,370,570

1,022,081

821,976

Long-Lived Assets

487,536

[9]

392,424

[9]

487,536

[9]

392,424

[9]

368,897

[9]

Iceland [Member]

Revenues from External Customers and Long-Lived Assets [Line Items]

Net sales

560,472

432,232

450,135

Long-Lived Assets

831,507

[9]

853,636

[9]

831,507

[9]

853,636

[9]

869,809

[9]

Others [Member]

Revenues from External Customers and Long-Lived Assets [Line Items]

Long-Lived Assets

$95,752

[9]

$93,075

[9]

$95,752

[9]

$93,075

[9]

$50,223

[9]

[1]

The fourth quarter of 2014 net income included a benefit of $7,943 for the gain on remeasurement of contingent consideration and a benefit of $1,318 for gain on remeasurement of our equity investment in Mt. Holly. Results were negatively impacted by $4,964 in non-cash, non-recurring pension charges and by $2,616 related to the separation of former senior executives.

[2]

The third quarter of 2014 net income reflects higher aluminum prices and lower power prices in the Midwestern U.S.

[3]

The second quarter of 2014 net income reflects higher aluminum prices and lower power prices in the Midwestern U.S. Results were negatively impacted by a charge of $500 for the finalization of a legal settlement.

[4]

The first quarter of 2014 cost of sales included a benefit of $5,534 related to deferred power contract liability amortization. Results were negatively impacted by a $3,100 charge for increased legal reserves.

[5]

The fourth quarter of 2013 cost of sales included a benefit of $16,570 related to deferred power contract liability amortization. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a credit of $9,040. The financial results also include an $8,400 charge relating to the separation of our former CEO.

[6]

The third quarter of 2013 cost of sales included an $11,720 benefit for deferred power contract liability amortization. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a credit of $5,762.

[7]

The second quarter of 2013 amounts differ from our reported second quarter results due to purchase price accounting adjustments related to the Sebree acquisition which were retroactively applied to the second quarter of 2013. The second quarter of 2013 net loss included a gain on bargain purchase of $5,253 and power contract amortization of $2,741 associated with the Sebree acquisition. Results were negatively impacted by a charge of $3,272 for the early extinguishment of our 8.0% Notes and a charge for severance and other expenses of $1,750 related to our corporate headquarters relocation. During the quarter, inventory that had previously been written down to its market basis was consumed into cost of goods sold and inventory at the end of the quarter was written down to its market basis. The net impact of these valuation adjustments on costs of goods sold was a charge of $10,211.

[8]

The first quarter of 2013 net income included a net benefit of $2,225 related to a litigation reserve adjustment and an unrealized gain of $15,722 related to a LME-based contingent obligation. Results were negatively impacted by severance and other expenses of $2,213 related to our corporate headquarters relocation. The net effect of reporting inventory on a lower of cost or market basis was a charge to cost of goods sold of $5,838 in the quarter.

[9]

Includes long-lived assets other than financial instruments.

Business_Segments_Major_Custom

Business Segments Major Customers (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue, Major Customer [Line Items]
Major customer, percentage revenue, net	10.00%
Glencore [Member]
Revenue, Major Customer [Line Items]
Major customer, Revenue, net	$1,262,101	$511,051	$552,299
Southwire [Member]
Revenue, Major Customer [Line Items]
Major customer, Revenue, net	226,740	312,102	346,311
RTA [Member]
Revenue, Major Customer [Line Items]
Major customer, Revenue, net	0	223,353	0
BHP Billiton [Member]
Revenue, Major Customer [Line Items]
Major customer, Revenue, net	$0	$191,445	$202,500

Related_Party_Transactions_Det

Related Party Transactions (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Related Party Transaction [Line Items]
Net sales to Glencore	$1,262,101	$511,051	$552,299
Glencore [Member]
Related Party Transaction [Line Items]
Net sales to Glencore	1,262,101	511,051	552,299
Purchases from Glencore	285,167	173,693	145,589
Noncontrolling Interest [Member]
Related Party Transaction [Line Items]
Purchases from BHH	$47,804	$86,678	$39,337
BHH [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage	40.00%

Subsequent_events_Subsequent_e

Subsequent events Subsequent events (Details) (USD $)	12 Months Ended	41 Months Ended	2 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2014	Feb. 27, 2015	Feb. 26, 2015
Subsequent Event [Line Items]
Treasury stock acquired, Aggregate purchase price	$4,033	$49,924
Stock repurchase program, Remaining authorized repurchase amount		10,076
Share repurchase program expansion [Member]
Subsequent Event [Line Items]
Stock Repurchase Program, Additional authorized amount				20,000
Treasury stock acquired, Aggregate purchase price			5,840
Stock repurchase program, Remaining authorized repurchase amount				$24,276

Schedule_II_Valuation_and_Qual1

Schedule II - Valuation and Qualifying Accounts (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance, valuation allowance	$748,283	$765,023	$656,352
Allowance for doubtful trade accounts receivable [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance, valuation allowance	1,000	734	734	734
Charged to Cost and Expense	0	0	0
Charged to Other Accounts	266	0	0
Deductions	0	0	0
Deferred tax asset - valuation allowance [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance, valuation allowance	748,283	765,023	656,352	773,714
Charged to Cost and Expense	0	0	0
Charged to Other Accounts	-16,740	108,671	-117,362
Deductions	$0	$0	$0