Supplementary Financial Information On Oil And Natural Gas Exploration Development and Production (Details 2)	12 Months Ended
	Dec. 31, 2012 bbl	Dec. 31, 2011 bbl
Natural Gas [Member]
Beginning of year	691,100	714,780
Purchase (sale) of oil and natural gas properties in place
Discoveries and extensions	7,900
Revisions	41,992	21,002
Production	(61,582)	(44,682)
Proved reserves, at end of year	679,410	691,100
Oil [Member]
Beginning of year	8,040
Purchase (sale) of oil and natural gas properties in place	(480)	7,053
Discoveries and extensions	10,880
Revisions	7,509	1,559
Production	(1,659)	(572)
Proved reserves, at end of year	24,290	8,040