Business Segments - Revenue Components of Mineral Resources Segment (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Revenue from External Customer [Line Items]
Commercial/industrial revenues	$ 13,079	$ 11,946	$ 32,881	$ 35,579
Income (loss)	(1,765)	(3,300)	(4,363)	(3,230)
Mineral resources
Revenue from External Customer [Line Items]
Income (loss)	458	716	5,892	7,151
Operating Segments \| Mineral resources
Revenue from External Customer [Line Items]
Commercial/industrial revenues	1,125	1,322	13,052	14,174
Operating Segments \| Mineral resources \| Oil and gas
Revenue from External Customer [Line Items]
Commercial/industrial revenues	394	640	1,163	2,333
Operating Segments \| Mineral resources \| Water sales
Revenue from External Customer [Line Items]
Commercial/industrial revenues	0	0	9,601	10,165
Operating Segments \| Mineral resources \| Rock aggregate
Revenue from External Customer [Line Items]
Commercial/industrial revenues	306	282	813	629
Operating Segments \| Mineral resources \| Cement
Revenue from External Customer [Line Items]
Commercial/industrial revenues	367	373	996	916
Operating Segments \| Mineral resources \| Land lease for oil exploration
Revenue from External Customer [Line Items]
Commercial/industrial revenues	25	27	151	131
Operating Segments \| Mineral resources \| Reimbursable costs
Revenue from External Customer [Line Items]
Commercial/industrial revenues	$ 33	$ 0	$ 328	$ 0

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Sum of operating profit and nonoperating income or expense before Income or Loss from equity method investments, income taxes, extraordinary items, and noncontrolling interest.

+ 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=26872669&loc=d3e20235-122688

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