Supplemental Oil And Gas Disclosures (Schedule Of Proved Developed And Undeveloped Oil And Gas Reserve Quantities) (Details)	12 Months Ended
	Dec. 31, 2011 bbl		Dec. 31, 2010 bbl		Dec. 31, 2009 bbl		Jun. 02, 2010 bbl
Oil [Member]
Reserve Quantities [Line Items]
Beginning of year	17,494,000		11,669,000		9,699,000
Revision of previous estimates	374,000	[1]	434,000	[1]	459,000	[1]
Extensions and discoveries	3,477,000		3,473,000		2,135,000
Infill reserves in existing proved fields	1,229,000		2,152,000		618,000	[2]
Purchases of minerals in place	192,000		1,293,000		44,000
Production	(2,511,000)		(1,521,000)		(1,286,000)
Sales	0		(6,000)
End of Year	20,255,000		17,494,000		11,669,000
Beginning of year, developed	12,773,000		9,183,000		7,508,000		511,000
End of year, developed	15,618,000		12,773,000		9,183,000		511,000
Beginning of year, undeveloped	4,721,000		2,486,000		2,191,000
End of year, undeveloped	4,637,000		4,721,000		2,486,000
Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Beginning of year	16,117,000		14,653,000		10,171,000
Revision of previous estimates	2,112,000	[1]	(1,559,000)	[1]	2,793,000	[1]
Extensions and discoveries	3,924,000		878,000		1,996,000
Infill reserves in existing proved fields	1,780,000		3,482,000		1,174,000	[2]
Purchases of minerals in place	393,000		212,000		7,000
Production	(2,239,000)		(1,549,000)		(1,488,000)
Sales	0		0
End of Year	22,087,000		16,117,000		14,653,000
Beginning of year, developed	12,088,000		11,538,000		8,638,000
End of year, developed	16,649,000		12,088,000		11,538,000
Beginning of year, undeveloped	4,029,000		3,115,000		1,533,000
End of year, undeveloped	5,438,000		4,029,000		3,115,000
Natural Gas [Member]
Reserve Quantities [Line Items]
Beginning of year	420,486,000		419,061,000		450,135,000
Revision of previous estimates	(30,510,000)	[1]	(25,007,000)	[1]	(57,393,000)	[1]
Extensions and discoveries	39,836,000		31,328,000		50,480,000
Infill reserves in existing proved fields	15,592,000		34,128,000		19,872,000	[2]
Purchases of minerals in place	40,835,000		1,732,000		30,000
Production	(44,104,000)		(40,756,000)		(44,063,000)
Sales	0		0
End of Year	442,135,000		420,486,000		419,061,000
Beginning of year, developed	346,928,000		338,217,000		355,824,000
End of year, developed	372,311,000		346,928,000		338,217,000
Beginning of year, undeveloped	73,558,000		80,844,000		94,311,000
End of year, undeveloped	69,824,000		73,558,000		80,844,000

[1] Natural gas revisions of previous estimates decreased primarily due to a decline in natural gas prices.

[2] Previously included in 'Extensions, discoveries and other additions'.