Inventories (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Inventory Disclosure [Abstract]
Coal	$ 16,025	$ 17,695
Mining supplies	33,691	29,856
Total inventories	$ 49,716	$ 47,551

Carrying amount as of the balance sheet date of coal, which is a combustible rock or minerals which are extracted from the ground and used as fuel.

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- Definition

Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

+ References

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Amount before valuation and LIFO reserves of other supplies used within the manufacturing or production process expected to be consumed within one year or operating cycle, if longer.

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-Name Accounting Standards Codification
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