Supplemental Oil and Gas Disclosures (Unaudited) - Summary of Estimated Quantities of Proved Developed Oil and Natural Gas Reserves (Detail)	12 Months Ended
	Dec. 31, 2014 bbl		Dec. 31, 2013 bbl		Dec. 31, 2012 bbl		Dec. 31, 2010 bbl
Oil [Member]
Reserve Quantities [Line Items]
Proved developed reserves	5,269,000	[1]	3,893,000	[1]	2,416,000	[1]
Proved undeveloped reserves	2,403,000	[1]	1,931,000	[1]	804,000	[1]
Ending Balance	7,672,000	[1]	5,824,000	[1]	3,220,000	[1]
Natural Gas [Member]
Reserve Quantities [Line Items]
Proved developed reserves	12,599,000		13,717,000		13,020,000
Proved undeveloped reserves	1,801,000		2,245,000		1,274,000
Ending Balance	14,400,000		15,962,000		14,294,000
Consolidated Entities [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates	608,000		800,000
Consolidated Entities [Member] | Oil [Member]
Reserve Quantities [Line Items]
Beginning Balance	5,824,000	[1]	3,220,000	[1]			1,064,000	[1]
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates	608,000	[1]	182,000	[1]	45,000	[1]
Extensions and discoveries	2,191,000	[1]	3,085,000	[1]	86,000	[1]
Proved Developed and Undeveloped Reserves, Sales of Minerals in Place	(105,000)	[1]
Acquisitions	85,000	[1]	35,000	[1]	2,396,000	[1]
Production	(931,000)	[1]	(698,000)	[1]	(371,000)	[1]
Ending Balance	7,672,000	[1]	5,824,000	[1]	3,220,000	[1]	1,064,000	[1]
Consolidated Entities [Member] | Natural Gas [Member]
Reserve Quantities [Line Items]
Beginning Balance	13,630,000		11,722,000				8,203,000
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates	293,000		1,243,000		(2,163,000)
Extensions and discoveries	774,000		2,046,000		241,000
Proved Developed and Undeveloped Reserves, Sales of Minerals in Place	(218,000)
Acquisitions	31,000		531,000		7,109,000
Production	(1,861,000)		(1,912,000)		(1,668,000)
Ending Balance	12,649,000		13,630,000		11,722,000		8,203,000
Equity Method Investee [Member] | Oil [Member]
Reserve Quantities [Line Items]
Beginning Balance	0	[1]	0	[1]			0	[1]
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates	0	[1]	0	[1]	0	[1]
Production	0	[1]	0	[1]	0	[1]
Ending Balance	0	[1]	0	[1]	0	[1]	0	[1]
Equity Method Investee [Member] | Natural Gas [Member]
Reserve Quantities [Line Items]
Beginning Balance	2,332,000		2,572,000				3,283,000
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates	(382,000)		7,000		(390,000)
Production	(199,000)		(247,000)		(321,000)
Ending Balance	1,751,000		2,332,000		2,572,000		3,283,000

[1] Includes natural gas liquids (NGLs).