Segment Information - Segment Revenues and Earnings (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Total revenues	$ 57,430	$ 83,013	$ 105,235	$ 167,618
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	(55,251)	22,873	(67,768)	35,865
Segment Earnings [Member]
Segment Reporting Information [Line Items]
Total revenues	57,430	83,013	105,235	167,618
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	(41,383)	38,898	(35,649)	62,752
Segment Earnings [Member] | Real estate [Member]
Segment Reporting Information [Line Items]
Total revenues	39,409	55,173	72,239	120,653
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	15,527	27,297	24,593	50,872
Segment Earnings [Member] | Oil And Gas [Member]
Segment Reporting Information [Line Items]
Total revenues	16,165	24,377	29,350	41,931
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	(56,867)	9,522	(59,808)	10,329
Segment Earnings [Member] | Other natural resources [Member]
Segment Reporting Information [Line Items]
Total revenues	1,856	3,463	3,646	5,034
Segment Reporting Information Income (Loss) From Continuing Operations Before Income Taxes Attributable To Parent	(43)	2,079	(434)	1,551
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	(13,868)	(16,025)	(32,119)	(26,887)
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	(5,177)	(5,566)	(11,197)	(10,734)
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	(23)	(3,219)	(3,481)	(3,532)
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	(8,715)	(7,370)	(17,536)	(12,873)
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	$ 47	$ 130	$ 95	$ 252