Segment Information - Assets Allocated by Segment (Detail) - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Total Assets		$ 948,052	$ 972,246
Cash and cash equivalents		142,646	96,442	$ 126,262	$ 170,127
Income taxes receivable		14,359	12,056
Operating Segments | Real estate
Segment Reporting Information [Line Items]
Total Assets		666,726	691,238
Operating Segments | Oil and Gas
Segment Reporting Information [Line Items]
Total Assets		97,346	144,436
Operating Segments | Other natural resources
Segment Reporting Information [Line Items]
Total Assets		19,025	19,106
Items not allocated to segments
Segment Reporting Information [Line Items]
Total Assets	[1]	$ 164,955	$ 117,466

[1] Assets not allocated to segments at first quarter-end 2016 principally consist of cash and cash equivalents of $142,646,000 and an income tax receivable of $14,359,000. Assets not allocated to segments at year-end 2015 principally consist of cash and cash equivalents of $96,442,000 and an income tax receivable of $12,056,000.