v3.19.1

INVENTORY AND LONG-TERM PARTS INVENTORY (Summary of Inventory) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Finished goods product inventory	$ 48,370	$ 54,577
In-process mineral inventory	24,325	19,822
Total product inventory	72,695	74,399
Current parts inventory, net	9,351	8,727
Total current inventory, net	82,046	83,126
Long-term parts inventory, net	30,031	30,611
Total inventory, net	$ 112,077	$ 113,737

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- Definition

Including current and noncurrent portions, aggregate carrying amount of inventories, less all valuation and other allowances, as of the balance sheet date.

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- Definition

Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date of parts inventory, including critical spares, that is not expected to be utilized within a period of one year.

+ References

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- Definition

Carrying amount (lower of cost or market) as of the balance sheet date of product inventories less all valuation and other allowances.

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- Definition

Amount before valuation and LIFO reserves of completed merchandise or goods expected to be sold within one year or operating cycle, if longer.

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

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Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date for elements of machinery or equipment held for the purpose of replacing similar parts in the course of repair or maintenance.

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Amount before valuation and LIFO reserves of merchandise or goods in the production process expected to be completed within one year or operating cycle, if longer.

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