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Unrecorded Unconditional Purchase Obligation (Details) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Purchase Commitment [Member]    
Unrecorded Unconditional Purchase Obligation [Line Items]    
Less than 1 year $ 209,797  
1 - 3 years 285,224  
3 - 5 years 243,534  
More than 5 years 622,509  
Total Purchase Obligations 1,361,064  
Murray Energy [Member]    
Unrecorded Unconditional Purchase Obligation [Line Items]    
Contractual Obligation $ 1,362 $ 1,228