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Inventories (Tables)
12 Months Ended
Dec. 31, 2017
Inventories  
Schedule of inventories, net
20172016
Materials and supplies$68,461$67,933
Less: Obsolescence allowance(1,094)(956)
Material and supplies, net67,36766,977
Coal inventory5,5371,706
Inventories, net$72,904$68,683