Supplemental Oil and Gas Disclosures (Unaudited) - Summary of Estimated Quantities of Proved Developed Oil and Natural Gas Reserves (Detail) bbl in Thousands, Mcf in Thousands		12 Months Ended
		Dec. 31, 2015 bbl Mcf	Dec. 31, 2015 bbl Mcf	Dec. 31, 2014 bbl Mcf	Dec. 31, 2013 bbl Mcf
Oil [Member]
Reserve Quantities [Line Items]
Beginning Balance	[1]	7,672		5,824
Proved developed reserves	[1]	5,179	5,179	5,269	3,893
Proved undeveloped reserves	[1]	0	0	2,403	1,931
Ending Balance	[1]	5,179		7,672	5,824
Natural Gas [Member]
Reserve Quantities [Line Items]
Beginning Balance | Mcf			14,400	15,962
Proved developed reserves | Mcf		9,220	9,220	12,599	13,717
Proved undeveloped reserves | Mcf		0	0	1,801	2,245
Ending Balance | Mcf			9,220	14,400	15,962
Consolidated Entities [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates				(608)	(1,243)
Consolidated Entities [Member] | Oil [Member]
Reserve Quantities [Line Items]
Beginning Balance	[1]	7,672		5,824	3,220
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates	[1]	(855)		(608)	(182)
Extensions and discoveries	[1]	224		2,191	3,085
Proved Developed and Undeveloped Reserves, Sales of Minerals in Place	[1]	(704)		(105)
Acquisitions	[1]	0		85	35
Production	[1]	(1,158)		(931)	(698)
Ending Balance	[1]	5,179		7,672	5,824
Consolidated Entities [Member] | Natural Gas [Member]
Reserve Quantities [Line Items]
Beginning Balance | Mcf			12,649	13,630	11,722
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates		(1,995)	(1,675)	(293)	(1,243)
Extensions and discoveries | Mcf			173	774	2,046
Proved Developed and Undeveloped Reserves, Sales of Minerals in Place | Mcf			(1,223)	(218)
Acquisitions | Mcf			0	31	531
Production | Mcf			(1,967)	(1,861)	(1,912)
Ending Balance | Mcf			7,957	12,649	13,630
Equity Method Investee [Member] | Oil [Member]
Reserve Quantities [Line Items]
Beginning Balance	[1]	0		0	0
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates	[1]	0		0	0
Production	[1]	0		0	0
Ending Balance	[1]	0		0	0
Equity Method Investee [Member] | Natural Gas [Member]
Reserve Quantities [Line Items]
Beginning Balance | Mcf			1,751	2,332	2,572
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates | Mcf			320	382	(7)
Production | Mcf			(168)	(199)	(247)
Ending Balance | Mcf			1,263	1,751	2,332

[1] Includes natural gas liquids (NGLs).