Segment Information - Segment Revenues and Earnings (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
Total revenues	$ 47,805	$ 84,605
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	(12,517)	12,992
Segment Earnings [Member]
Segment Reporting Information [Line Items]
Total revenues	47,805	84,605
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	5,734	23,854
Segment Earnings [Member] | Real estate [Member]
Segment Reporting Information [Line Items]
Total revenues	32,830	65,480
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	9,066	23,575
Segment Earnings [Member] | Oil And Gas [Member]
Segment Reporting Information [Line Items]
Total revenues	13,185	17,554
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	(2,941)	807
Segment Earnings [Member] | Other natural resources [Member]
Segment Reporting Information [Line Items]
Total revenues	1,790	1,571
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	(391)	(528)
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	(18,251)	(10,862)
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	(6,020)	(5,168)
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	(3,458)	(313)
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	(8,821)	(5,503)
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	$ 48	$ 122