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INVENTORIES (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
INVENTORIES |  |  |
Coal | $ 19,756 | $ 63,645 |
Supplies (net of reserve for obsolescence of $5,547 and $5,555, respectively) | 36,651 | 37,660 |
Total inventories, net | 56,407 | 101,305 |
Reserve for obsolescence | 5,547 | 5,555 |
Reduce inventory carrying value to market | $ 3,245 | $ 4,895 | $ 1,455

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