Supplemental Oil and Gas Disclosures (Unaudited) - Estimates of Future Cash Flows from Proved Developed Oil and Natural Gas Reserves (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Standardized measure of discounted future net cash flows	$ 67,498	$ 165,616	$ 136,853	$ 107,956
Consolidated Entities [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Cash Inflows	216,588	665,657	544,098
Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Production Costs	(93,623)	(271,735)	(231,801)
Future income tax expenses	(22,218)	(106,002)	(77,361)
Future net cash flows	100,747	287,920	234,936
10% annual discount for estimated timing of cash flows	(33,951)	(124,079)	(99,383)
Standardized measure of discounted future net cash flows	66,796	163,841	135,553	106,543
Equity Method Investee [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Cash Inflows	2,283	6,186	4,765
Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Production Costs	(245)	(664)	(512)
Future income tax expenses	(774)	(2,098)	(1,616)
Future net cash flows	1,264	3,424	2,637
10% annual discount for estimated timing of cash flows	(562)	(1,649)	(1,337)
Standardized measure of discounted future net cash flows	$ 702	$ 1,775	$ 1,300	$ 1,413