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Concentration of Credit Risk and Major Customers (Tables)
 12 Months Ended
Dec. 31, 2017
Risks and Uncertainties [Abstract]  
Schedule of Concentration of Credit Risk
Concentration of credit risk is summarized below:
 
 
December 31,
 
 
2017
 
2016
Thermal coal utilities
 
$
69,550

 
$
62,525

Coal brokers and distributors
 
56,146

 
28,955

Other
 
5,849

 
4,227

Total Accounts Receivable Trade
 
$
131,545

 
$
95,707