Inventories - Schedule of Inventories (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Raw materials	$ 24,249	$ 23,964
Work-in-progress	42,840	29,198
Finished goods	24,083	20,046
Supplies	16,389	10,371
Inventories	$ 107,561	$ 83,579

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Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date of merchandise or goods held by the company that are readily available for sale.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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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 of unprocessed items to be consumed in the manufacturing or production process.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Carrying amount, net of reserves and adjustments, as of the balance sheet date of merchandise or goods which are partially completed. This inventory is generally comprised of raw materials, labor and factory overhead costs, which require further materials, labor and overhead to be converted into finished goods, and which generally require the use of estimates to determine percentage complete and pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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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.

+ References

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