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Fair value measurements | 3 Months Ended | 12 Months Ended
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Mar. 31, 2017 | Dec. 31, 2016
Fair Value Disclosures [Abstract] |  |
Fair value measurements | Fair value measurements The following section describes the valuation methodology used to measure our financial assets and liabilities that were accounted for at fair value and are categorized based on the fair value hierarchy described in Accounting Standards Codification ("ASC") 820, "Fair Value Measurements and Disclosures."
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 financial sales | 2 | Quoted market prices
Fixed for floating swaps | 3 | Quoted market prices, management's estimates of future U.S. Midwest premium
E.ON contingent obligation | 3 | Quoted market prices, 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.
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. 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 date of the event or change in circumstances that caused the transfer. 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.
Recurring Fair Value Measurements | As of March 31, 2017
| Level 1 | Level 2 | Level 3 | Total
ASSETS: |  |  |  |
Cash equivalents | $ | 103,286 |  | $ | — |  | $ | — |  | $ | 103,286 |
Trust assets | 3,138 |  | — |  | — |  | 3,138 |
Surety bonds | 1,618 |  | — |  | — |  | 1,618 |
Derivatives | — |  | — |  | 1,610 |  | 1,610 |
TOTAL | $ | 108,042 |  | $ | — |  | $ | 1,610 |  | $ | 109,652 |
LIABILITIES: |  |  |  |
E.ON contingent obligation - net | $ | — |  | $ | — |  | $ | — |  | $ | — |
Derivatives | — |  | 13,015 |  | 1,900 |  | 14,915 |
TOTAL | $ | — |  | $ | 13,015 |  | $ | 1,900 |  | $ | 14,915 |
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 |
Derivatives | — |  | — |  | 925 |  | 925 |
TOTAL | $ | 84,035 |  | $ | — |  | $ | 925 |  | $ | 84,960 |
LIABILITIES: |  |  |  |
E.ON contingent obligation – net | $ | — |  | $ | — |  | $ | — |  | $ | — |
Derivatives | — |  | — |  | 253 |  | 253 |
TOTAL | $ | — |  | $ | — |  | $ | 253 |  | $ | 253 |
| 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." 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
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.
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. 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 date of the event or change in circumstances that caused the transfer.
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 The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14172-108612 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14064-108612 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 21 -URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13537-108611 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 16 -URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13504-108611 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13433-108611 + Details
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