Segment Information - Assets Allocated by Segment (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Total Assets	$ 1,236,971		$ 1,258,199
Cash and cash equivalents	126,262		170,127		147,979	192,307
Deferred tax asset, net	44,583		40,624
Operating Segments [Member] | Real estate [Member]
Segment Reporting Information [Line Items]
Total Assets	670,067		654,774
Operating Segments [Member] | Oil And Gas [Member]
Segment Reporting Information [Line Items]
Total Assets	352,695		342,703
Operating Segments [Member] | Other natural resources [Member]
Segment Reporting Information [Line Items]
Total Assets	20,077		22,531
Items not allocated to segments [Member] | Assets not allocated to segments [Member]
Segment Reporting Information [Line Items]
Total Assets	$ 194,132	[1]	$ 238,191	[1]

[1] Assets not allocated to segments at first quarter-end 2015 principally consist of cash and cash equivalents of $126,262,000 and a net deferred tax asset of $44,583,000. Assets not allocated to segments at year-end 2014 principally consist of cash and cash equivalents of $170,127,000 and a net deferred tax asset of $40,624,000.