Segment Information - Segment Revenues and Earnings (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Segment Reporting Information [Line Items]
Total revenues	$ 84,605	$ 97,471
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	12,992	5,944
Segment Earnings [Member]
Segment Reporting Information [Line Items]
Total revenues	84,605	97,471
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	23,854	25,825
Segment Earnings [Member] | Real estate [Member]
Segment Reporting Information [Line Items]
Total revenues	65,480	78,689
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	23,575	19,446
Segment Earnings [Member] | Oil and gas [Member]
Segment Reporting Information [Line Items]
Total revenues	17,554	15,504
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	807	5,127
Segment Earnings [Member] | Other natural resources [Member]
Segment Reporting Information [Line Items]
Total revenues	1,571	3,278
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	(528)	1,252
Items not allocated to segments [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	(10,862)	(19,881)
Items not allocated to segments [Member] | General and administrative expense [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	5,168	4,958
Items not allocated to segments [Member] | Share-based compensation expense [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	313	10,415
Items not allocated to segments [Member] | Interest expense [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	5,503	4,539
Items not allocated to segments [Member] | Other corporate non-operating income [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	$ 122	$ 31