Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash
-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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Carrying amount as of the balance sheet date of income taxes previously overpaid to tax authorities (such as U.S. Federal, state and local tax authorities) representing refunds of overpayments or recoveries based on agreed-upon resolutions of disputes. Also called income tax refund receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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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No definition available.

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Segment Information - Assets Allocated by Segment (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Total Assets	$ 768,119	$ 733,208
Cash and cash equivalents	381,390	265,798	$ 107,421	$ 96,442
Income taxes receivable	0	10,867
Discontinued Operations
Segment Reporting Information [Line Items]
Total Assets	1	14
Items Not Allocated to Segments \| Continuing Operations
Segment Reporting Information [Line Items]
Total Assets	383,550	279,694
Cash and cash equivalents	381,390	265,798
Income taxes receivable		10,867
Real estate \| Operating Segments \| Continuing Operations
Segment Reporting Information [Line Items]
Total Assets	374,246	403,062
Mineral resources \| Operating Segments \| Continuing Operations
Segment Reporting Information [Line Items]
Total Assets	188	38,907
Other \| Operating Segments \| Continuing Operations
Segment Reporting Information [Line Items]
Total Assets	$ 10,134	$ 11,531