Derivative Instruments (Narrative) (Details)  | 
6 Months Ended | 
|---|---|
| 
 Jun. 30, 2016  
MMBTU / d  
$ / MMBTU 
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| Derivative [Line Items] | |
| Derivative, Extension Option Term | 12 months | 
| January 2017 - December 2017 | |
| Derivative [Line Items] | |
| Daily Volume | MMBTU / d | 30,000 | 
| Weighted Average Price (in usd per MMBtu) | $ / MMBTU | 3.33 | 
| January 2017 - December 2017 | Short | |
| Derivative [Line Items] | |
| Daily Volume | MMBTU / d | 30,000 | 
| Weighted Average Price (in usd per MMBtu) | $ / MMBTU | 3.33 | 
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- Definition Derivative, Extension Option Term No definition available. 
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- Definition Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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- Definition Average fixed price related to the group of price risk swap derivatives. No definition available. 
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- Details 
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- Details 
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