Reporting Segments and Related Information - Revenue Components of Mineral Resources Segment (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revenue from External Customer [Line Items]
Commercial/industrial revenues	$ 6,365	$ 6,849	$ 12,067	$ 19,802
Income (loss)	(1,833)	(2,950)	(5,306)	(2,598)
Mineral resources
Revenue from External Customer [Line Items]
Income (loss)	990	1,387	1,667	5,434
Mineral resources \| Operating Segments
Revenue from External Customer [Line Items]
Commercial/industrial revenues	1,519	3,187	3,520	11,927
Mineral resources \| Operating Segments \| Oil and gas
Revenue from External Customer [Line Items]
Commercial/industrial revenues	429	383	805	769
Mineral resources \| Operating Segments \| Water sales
Revenue from External Customer [Line Items]
Commercial/industrial revenues	146	1,810	1,254	9,601
Mineral resources \| Operating Segments \| Rock aggregate
Revenue from External Customer [Line Items]
Commercial/industrial revenues	248	305	428	507
Mineral resources \| Operating Segments \| Cement
Revenue from External Customer [Line Items]
Commercial/industrial revenues	519	369	797	629
Mineral resources \| Operating Segments \| Land lease for oil exploration
Revenue from External Customer [Line Items]
Commercial/industrial revenues	0	25	25	126
Mineral resources \| Operating Segments \| Reimbursable costs
Revenue from External Customer [Line Items]
Commercial/industrial revenues	$ 177	$ 295	$ 211	$ 295

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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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