Supplemental Oil And Gas Disclosures (Schedule Of Proved Developed And Undeveloped Oil And Gas Reserve Quantities) (Details)	12 Months Ended
	Dec. 31, 2012 bbl	Dec. 31, 2011 bbl	Dec. 31, 2010 bbl
Oil [Member] (bbls)
Reserve Quantities [Line Items]
Beginning of year	20,255,000	17,494,000	11,669,000
Revision of previous estimates	(1,747,000)	374,000	434,000	[1]
Extensions and discoveries	5,014,000	3,477,000	3,473,000
Infill reserves in existing proved fields	4,196,000	1,229,000	2,152,000
Purchases of minerals in place	2,830,000	192,000	1,293,000
Production	(3,279,000)	(2,511,000)	(1,521,000)
Sales	(5,271,000)	0	(6,000)
End of Year	21,998,000	20,255,000	17,494,000
Beginning of year, developed	15,618,000	12,773,000	9,183,000
End of year, developed	16,441,000	15,618,000	12,773,000
Beginning of year, undeveloped	4,637,000	4,721,000	2,486,000
End of year, undeveloped	5,557,000	4,637,000	4,721,000
Natural Gas Liquids [Member] (bbls)
Reserve Quantities [Line Items]
Beginning of year	22,087,000	16,117,000	14,653,000
Revision of previous estimates	(2,682,000)	2,112,000	(1,559,000)	[1]
Extensions and discoveries	4,819,000	3,924,000	878,000
Infill reserves in existing proved fields	3,018,000	1,780,000	3,482,000
Purchases of minerals in place	11,098,000	393,000	212,000
Production	(2,796,000)	(2,239,000)	(1,549,000)
Sales	(378,000)	0	0
End of Year	35,166,000	22,087,000	16,117,000
Beginning of year, developed	16,649,000	12,088,000	11,538,000
End of year, developed	25,657,000	16,649,000	12,088,000
Beginning of year, undeveloped	5,438,000	4,029,000	3,115,000
End of year, undeveloped	9,509,000	5,438,000	4,029,000
Natural Gas [Member] (Mcf)
Reserve Quantities [Line Items]
Beginning of year	442,135,000	420,486,000	419,061,000
Revision of previous estimates	(55,110,000)	(30,510,000)	(25,007,000)	[1]
Extensions and discoveries	54,761,000	39,836,000	31,328,000
Infill reserves in existing proved fields	25,057,000	15,592,000	34,128,000
Purchases of minerals in place	141,494,000	40,835,000	1,732,000
Production	(48,930,000)	(44,104,000)	(40,756,000)
Sales	(3,760,000)	0	0
End of Year	555,647,000	442,135,000	420,486,000
Beginning of year, developed	372,311,000	346,928,000	338,217,000
End of year, developed	452,844,000	372,311,000	346,928,000
Beginning of year, undeveloped	69,824,000	73,558,000	80,844,000
End of year, undeveloped	102,803,000	69,824,000	73,558,000

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