Supplemental Oil and Gas Disclosures (Unaudited) - Estimates of Future Cash Flows from Proved Developed Oil and Natural Gas Reserves (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Total consolidated and our share of equity method ventures	$ 136,853	$ 107,956	$ 56,206
Consolidated Entities [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future cash inflows	544,098	322,098	142,043
Future production and development costs	(231,801)	(104,441)	(18,929)
Future income tax expenses	(77,361)	(50,350)	(38,681)
Future net cash flows	234,936	167,307	84,433
10% annual discount for estimated timing of cash flows	(99,383)	(60,764)	(31,735)
Standardized measure of discounted future net cash flows	135,553	106,543	52,698
Equity Method Investee [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future cash inflows	4,765	5,125	12,346
Future production and development costs	(512)	(551)	(1,731)
Future income tax expenses	(1,616)	(1,738)	(3,154)
Future net cash flows	2,637	2,836	7,461
10% annual discount for estimated timing of cash flows	(1,337)	(1,423)	(3,953)
Standardized measure of discounted future net cash flows	$ 1,300	$ 1,413	$ 3,508