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Fair value measurements (Tables) | 3 Months Ended
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Mar. 31, 2012
Fair Value Disclosures [Abstract] |
Schedule of valuation methodology used to measure 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
Primary aluminum put option contracts | 2 | Quoted London Metal Exchange (“LME”) forward market prices, historical volatility measurements and risk-adjusted discount rates
Natural gas forward financial contracts | 2 | Quoted natural gas forward market prices for primary aluminum and risk-adjusted discount rates
Power contract | 3 | Quoted LME forward market prices, power tariff prices, management’s estimate of future power usage and risk-adjusted discount rates
E.ON U.S. (“E.ON”) contingent obligation | 3 | Quoted LME forward market prices for primary aluminum, management’s estimates of the LME forward market prices for primary aluminum for periods beyond the quoted periods and management’s estimate of future level of operations at Century Aluminum of Kentucky, our wholly owned subsidiary (“CAKY”)
Primary aluminum sales premium contracts | 3 | Management’s estimates of future U.S. Midwest premium and risk-adjusted discount rates
(1) | Trust assets are currently invested in money market funds. 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 | 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.
Recurring Fair Value Measurements | As of March 31, 2012
| Level 1 | Level 2 | Level 3 | Total
ASSETS: |  |  |  |
Cash equivalents | $ | 175,321 |  | $ | — |  | $ | — |  | $ | 175,321 |
Trust assets | 15,572 |  | — |  | — |  | 15,572 |
Surety bond – workers comp insurance | 2,391 |  | — |  | — |  | 2,391 |
Primary aluminum put option contracts | — |  | 2,981 |  | — |  | 2,981 |
Power contract | — |  | — |  | 53 |  | 53 |
TOTAL | $ | 193,284 |  | $ | 2,981 |  | $ | 53 |  | $ | 196,318 |
LIABILITIES: |  |  |  |
Natural gas forward financial purchase contracts | $ | — |  | $ | 236 |  | $ | — |  | $ | 236 |
E.ON contingent obligation – net | — |  | — |  | 14,310 |  | 14,310 |
Primary aluminum sales contract – premium collar | — |  | — |  | 1,169 |  | 1,169 |
TOTAL | $ | — |  | $ | 236 |  | $ | 15,479 |  | $ | 15,715 |
Recurring Fair Value Measurements | As of December 31, 2011
| Level 1 | Level 2 | Level 3 | Total
ASSETS: |  |  |  |
Cash equivalents | $ | 176,284 |  | $ | — |  | $ | — |  | $ | 176,284 |
Trust assets | 15,889 |  | — |  | — |  | 15,889 |
Surety bonds – workers comp insurance | 2,391 |  | — |  | — |  | 2,391 |
Primary aluminum put option contracts | — |  | 9,331 |  | — |  | 9,331 |
Power contract | — |  | — |  | 106 |  | 106 |
TOTAL | $ | 194,564 |  | $ | 9,331 |  | $ | 106 |  | $ | 204,001 |
LIABILITIES: |  |  |  |
Natural gas forward financial purchase contracts | $ | — |  | $ | 281 |  | $ | — |  | $ | 281 |
E.ON contingent obligation – net | — |  | — |  | 13,958 |  | 13,958 |
Primary aluminum sales contract – premium collar | — |  | — |  | 908 |  | 908 |
TOTAL | $ | — |  | $ | 281 |  | $ | 14,866 |  | $ | 15,147 |
Change in level 3 fair value measurements |
Change in Level 3 Fair Value Measurements during the three months ended March 31,
| Derivative liabilities - net
| 2012 | 2011
Beginning balance, January 1, | $ | (14,760 | ) | $ | (13,802 | )
Total loss (realized/unrealized) included in earnings | (613 | ) | (473 | )
Settlements | (53 | ) | (36 | )
Ending balance, March 31, | $ | (15,426 | ) | $ | (14,311 | )
Amount of total loss included in earnings attributable to the change in unrealized losses (gains) relating to assets and liabilities held at March 31, | $ | 613 |  | $ | 473 |

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- Definition Schedule of Valuation Methodology for Assets and Liabilities at Fair Value [Table Text Block] + References No definition available. + Details
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- Definition Tabular disclosure of liabilities, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, by class that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3). Where the quoted price in an active market for the identical liability is not available, the Level 1 input is the quoted price of an identical liability when traded as an asset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19190-110258 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 157 -Paragraph 32 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 157 -Paragraph 6 -Footnote 4 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a),(b) -URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258 + Details
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- Definition Tabular disclosure of assets and liabilities, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Topic 820 -SubTopic 10 -Publisher FASB -Number -Article -Subparagraph -Name Accounting Standards Codification -Paragraph 1 -Section 50 -URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19190-110258 + Details
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