Reporting Segments and Related Information - Revenue Components of Mineral Resources Segment (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Revenue from External Customer [Line Items]
Commercial/industrial revenues	$ 5,702	$ 12,953
Income (loss)	(3,473)	352
Mineral resources
Revenue from External Customer [Line Items]
Income (loss)	677	4,047
Operating Segments \| Mineral resources
Revenue from External Customer [Line Items]
Commercial/industrial revenues	2,001	8,740
Operating Segments \| Mineral resources \| Oil and gas
Revenue from External Customer [Line Items]
Commercial/industrial revenues	376	386
Operating Segments \| Mineral resources \| Water sales
Revenue from External Customer [Line Items]
Commercial/industrial revenues	1,108	7,791
Operating Segments \| Mineral resources \| Rock aggregate
Revenue from External Customer [Line Items]
Commercial/industrial revenues	180	202
Operating Segments \| Mineral resources \| Cement
Revenue from External Customer [Line Items]
Commercial/industrial revenues	278	260
Operating Segments \| Mineral resources \| Land lease for oil exploration
Revenue from External Customer [Line Items]
Commercial/industrial revenues	25	101
Operating Segments \| Mineral resources \| Reimbursable costs
Revenue from External Customer [Line Items]
Commercial/industrial revenues	$ 34	$ 0

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Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(h)(1)(i))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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