Supplemental Oil and Gas Disclosures (Unaudited) - Information About Results of Operations of Oil and Natural Gas Interests (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Consolidated entities
Results of operations	$ (170,567)	$ (19,703)	$ 8,490
Consolidated Entities [Member]
Consolidated entities
Revenues	51,553	82,919	69,036
Production costs	(19,820)	(19,727)	(12,477)
Exploration costs	(11,864)	(17,416)	(10,486)
Depreciation, depletion, amortization	(28,774)	(29,442)	(19,552)
Results of Operations, Impairment of Oil and Gas Properties	(164,831)	(32,665)	(473)
Oil and gas administrative expenses	(11,700)	(17,000)	(14,407)
Results of Operations, Accretion of Asset Retirement Obligations	(144)	(121)	(94)
Income tax expenses	14,717	13,398	(3,471)
Results of operations	(170,863)	(20,054)	8,076
Equity Method Investee [Member]
Consolidated entities
Royalty revenues	428	786	801
Production costs	(102)	(105)	(123)
Oil and gas administrative expenses	(51)	(95)	(86)
Income tax expenses	21	(235)	(178)
Results of operations	$ 296	$ 351	$ 414