Supplemental Information On Oil And Gas Producing Activities (Net Proved Reserves) (Detail)		12 Months Ended
		Dec. 31, 2015 MMcf MBbls	Dec. 31, 2014 MMcf MBbls	Dec. 31, 2013 MMcf MBbls	Dec. 31, 2012 MMcf MBbls
Oil [Member]
Proved Reserves:
Beginning Balance		8,260	7,232	7,488
Production		(1,659)	(1,351)	(1,549)
Revisions of previous estimates		(3,746)	2,312	771
Extensions and discoveries			67	522
Ending Balance		2,855	8,260	7,232
Proved Developed Reserves		2,855	3,224	3,305	3,750
Gas [Member]
Proved Reserves:
Beginning Balance | MMcf	[1]	1,406	1,333	1,544
Production | MMcf	[1]	(181)	(227)	(325)
Revisions of previous estimates | MMcf	[1]	(172)	300	114
Ending Balance | MMcf	[1]	1,053	1,406	1,333
Proved Developed Reserves | MMcf		1,053	1,406	1,333	1,544
Natural Gas Liquids [Member]
Proved Reserves:
Natural gas liquids, MMcf to MBbl ratio		4.90%

[1] The natural gas reserves shown as of December 31, 2015 include natural gas liquids ("NGL") expressed as gas volumes using a ratio of 4.9 MMcf to 1 MBbl of NGL.