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Fair Value of Financial Instruments (Tables)
 12 Months Ended
Dec. 31, 2016
Fair Value Disclosures [Abstract]  
Fair Value, Assets Measured on Recurring Basis [Table Text Block]
The financial instruments measured at fair value on a recurring basis are summarized below:
 
Fair Value Measurements at
December 31, 2016
 
Fair Value Measurements at
December 31, 2015
Description
Level 1
 
Level 2
 
Level 3
 
Level 1
 
Level 2
 
Level 3
Gas Derivatives
$
—

 
$
(188,156
)
 
$
—

 
$
—

 
$
266,558

 
$
—

Murray Energy Guarantees
$
—

 
$
—

 
$
(1,362
)
 
$
—

 
$
—

 
$
(1,228
)