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Fair value measurements
12 Months Ended
Dec. 31, 2017
Fair Value Disclosures [Abstract]  
Fair value measurements
Fair value measurements

We measure certain of our assets and liabilities at fair value. Fair value represents 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. 

In general, reporting entities should apply valuation techniques to measure fair value that maximize the use of observable inputs and minimize the use of unobservable inputs. Observable inputs are developed using market data and reflect assumptions that market participants would use when pricing the asset or liability. Unobservable inputs are developed using the best information available about the assumptions that market participants would use when pricing the asset or liability.  

The fair value hierarchy provides transparency regarding the inputs we use to measure fair value. We categorize each fair value measurement in its entirety into the following three levels, based on the lowest level input that is significant to the entire measurement:
Level 1 Inputs – quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity can access at the measurement date.
Level 2 Inputs – quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly.
Level 3 Inputs – unobservable inputs for the asset or liability.
Recurring Fair Value Measurements
 
As of December 31, 2017
 
 
Level 1
 
Level 2
 
Level 3
 
Total
ASSETS:
 
 
 
 
 
 
 
 
Cash equivalents
 
$
142,819

 
$

 
$

 
$
142,819

Trust assets (1)
 
1,757

 

 

 
1,757

Surety bonds
 
1,618

 

 

 
1,618

     Derivative instruments
 

 

 
1,724

 
1,724

TOTAL
 
$
146,194

 
$

 
$
1,724

 
$
147,918

LIABILITIES:
 
 

 
 

 
 

 
 

Contingent obligation – net (2)
 
$

 
$

 
$

 
$

Derivative instruments
 

 

 
1,200

 
1,200

TOTAL
 
$

 
$

 
$
1,200

 
$
1,200

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 (1)
 
3,147

 

 

 
3,147

Surety bonds
 
1,874

 

 

 
1,874

Derivative instruments
 

 

 
925

 
925

TOTAL
 
$
84,035

 
$

 
$
925

 
$
84,960

LIABILITIES:
 
 

 
 

 
 

 
 

Contingent obligation – net (2)
 
$

 
$

 
$

 
$

Derivative instruments
 

 

 
253

 
253

TOTAL
 
$

 
$

 
$
253

 
$
253



(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.  
(2) 
See Note 5 Debt for additional information about the contingent obligation.




The following section describes the valuation techniques and inputs used for fair value measurements categorized within Level 2 or Level 3 of the fair value hierarchy:
Level 2 and Level 3 Fair Value Measurements:
Asset / Liability
 
Level
 
Valuation Techniques
 
Inputs
Fixed for floating swaps
 
3
 
Discounted cash flows
 
Quoted LME forward market, management's estimates of future U.S. Midwest premium
Power price swap
 
3
 
Discounted cash flows
 
Quoted Nordpool forward market, discount rate
Contingent obligation
 
3
 
Discounted cash flows
 
Quoted LME forward market, management’s estimates of the LME forward market prices for periods beyond the quoted periods, management’s estimate of future level of operations and discount rate

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.