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INVENTORIES (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
INVENTORIES [Abstract]      
Excess of current costs over carrying value of inventories $ 19,177 $ 17,946  
Positive (negative) effect of LIFO valuation method as compared to the FIFO method $ (1,231) $ 1,448 $ (438)