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Fair value measurements (Tables) | 12 Months Ended
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Dec. 31, 2016
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
Forward sales contracts | 2 | Quoted market prices
Fixed for floating swaps | 3 | Quoted LME forward market, management's estimates of future U.S. Midwest premium
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
(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 |
Recurring Fair Value Measurements | As of December 31, 2016
| Level 1 | Level 2 | Level 3 | Total
ASSETS: |  |  |  |
Cash equivalents | $ | 79,014 |  | $ | — |  | $ | — |  | $ | 79,014 |
Trust assets | 3,147 |  | — |  | — |  | 3,147 |
Surety bonds | 1,874 |  | — |  | — |  | 1,874 |
Derivative instruments | — |  | — |  | 925 |  | 925 |
TOTAL | $ | 84,035 |  | $ | — |  | $ | 925 |  | $ | 84,960 |
LIABILITIES: |  |  |  |  |  |  |  |
E.ON contingent obligation – net (1) | $ | — |  | $ | — |  | $ | — |  | $ | — |
Derivative instruments | — |  | — |  | 253 |  | 253 |
TOTAL | $ | — |  | $ | — |  | $ | 253 |  | $ | 253 |
Recurring Fair Value Measurements | As of December 31, 2015
| Level 1 | Level 2 | Level 3 | Total
ASSETS: |  |  |  |
Cash equivalents | $ | 102,675 |  | $ | — |  | $ | — |  | $ | 102,675 |
Trust assets | 5,226 |  | — |  | — |  | 5,226 |
Surety bonds | 1,870 |  | — |  | — |  | 1,870 |
TOTAL | $ | 109,771 |  | $ | — |  | $ | — |  | $ | 109,771 |
LIABILITIES: |  |  |  |  |  |  |  |
E.ON contingent obligation – net (1) | $ | — |  | $ | — |  | $ | — |  | $ | — |
TOTAL | $ | — |  | $ | — |  | $ | — |  | $ | — |
(1) | See Note 6 Debt for additional information about the E.ON contingent obligation.

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- Definition Tabular disclosure of the inputs and valuation techniques used to measure fair value, and a discussion of changes in valuation techniques and related inputs, if any, applied during the period to each separate class of assets, liabilities, and financial instruments classified in shareholders' equity that are measured on a recurring and/or nonrecurring basis. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=66048111&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 -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19190-110258 + Details
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