Inventories (Major Components of Inventories) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Petroleum products	$ 5,490		$ 8,731
Crude oil	29,930		29,873
Caustic soda	6,964		5,755
NaHS	13,040		8,277
Raw materials - Alkali operations	4,396		4,550
Work-in-process - Alkali operations	11,114		7,355
Finished goods, net - Alkali operations	11,182		14,075
Materials and supplies, net - Alkali operations	10,403		10,030
Other	1		7
Total	$ 92,520	$ 93,791	$ 88,653

Carrying amount of caustic soda as of the balance sheet date.

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Carrying amount of sodium hydrosulfide (NaHS) as of the balance sheet date.

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Carrying amount as of the balance sheet date of petroleum or crude oil.

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Carrying amount as of the balance sheet date of finished goods inventories for petroleum products, crude oil, petrochemical products, and other oil and gas inventories.

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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.

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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.

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Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date of products used directly or indirectly in the manufacturing or production process, which may or may not become part of the final product. May also include items used in the storage, presentation or transportation of physical goods.

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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.

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

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