Supplemental Oil and Gas Disclosures (Unaudited) - Information About Results of Operations of Oil and Natural Gas Interests (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012		Dec. 31, 2011
Consolidated entities
Results of operations	$ 8,490	$ 12,236		$ 9,765
Consolidated Entities [Member]
Consolidated entities
Revenues	69,036	36,204	[1]	19,239
Production costs	(12,477)	(4,472)	[1]	(1,492)
Exploration costs	(10,959)	(1,754)	[1]	(549)
Depreciation, depletion, amortization	(19,552)	(4,905)	[1]	(337)
Oil and gas administrative expenses	(14,407)	(8,332)	[1]	(4,445)
Results of Operations, Accretion of Asset Retirement Obligations	(94)	(26)	[1]	0
Income tax expenses	(3,471)	(4,841)	[1]	(3,645)
Results of operations	8,076	11,874	[1]	8,771
Equity Method Investee [Member]
Consolidated entities
Royalty revenues	801	770		1,882
Production costs	(123)	(138)		(260)
Oil and gas administrative expenses	(86)	(123)		(228)
Income tax expenses	(178)	(147)		(400)
Results of operations	$ 414	$ 362		$ 994

[1] 2012 includes only three months of operations from Credo due to our third quarter 2012 acquisition.