Supplemental Information about Oil & Gas Producing Activities (Unaudited) (Reserve Quantities) (Details)	12 Months Ended
	Dec. 31, 2011 mboe	Dec. 31, 2010 mboe	Dec. 31, 2009 mboe
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved developed and undeveloped reserves, Beginning of year	271,213	235,303	245,940
Revision of previous estimates	(28,446)	(3,522)	(2,975)
Improved recovery	0	1,700	0
Extensions and discoveries	30,600	20,019	18,100
Property sales	0	0	(21,100)
Production	(13,025)	(11,923)	(10,962)
Purchase of reserves in place	14,584	29,636	6,300
Proved developed and undeveloped reserves, End of year	274,926	271,213	235,303
Proved developed reserves, Beginning of year	133,678	125,456	134,879
Proved developed reserves, End of year	144,783	133,678	125,456
East Texas
Proved Developed and Undeveloped Reserves [Roll Forward]
Revision of previous estimates	(19,632)	(3,666)	(9,108)
Piceance
Proved Developed and Undeveloped Reserves [Roll Forward]
Revision of previous estimates	(5,779)	(3,890)
Uinta
Proved Developed and Undeveloped Reserves [Roll Forward]
Revision of previous estimates		(840)
Permian
Proved Developed and Undeveloped Reserves [Roll Forward]
Revision of previous estimates		971
California
Proved Developed and Undeveloped Reserves [Roll Forward]
Revision of previous estimates		3,903	398
Utah and Piceance
Proved Developed and Undeveloped Reserves [Roll Forward]
Revision of previous estimates			5,735
Utah
Proved Developed and Undeveloped Reserves [Roll Forward]
Revision of previous estimates	(2,576)
Oil
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved developed and undeveloped reserves, Beginning of year	166,181	129,940	125,251
Revision of previous estimates	(4,054)	4,288	2,786
Improved recovery	0	1,700	0
Extensions and discoveries	19,601	12,774	8,989
Property sales	0	0	0
Production	(9,041)	(7,925)	(7,186)
Purchase of reserves in place	13,193	25,404	100
Proved developed and undeveloped reserves, End of year	185,880	166,181	129,940
Proved developed reserves, Beginning of year	88,917	82,870	74,616
Proved developed reserves, End of year	107,849	88,917	82,870
Natural Gas
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved developed and undeveloped reserves, Beginning of year	630,192	632,178	724,135
Revision of previous estimates	(146,349)	(46,860)	(34,564)
Improved recovery	0	0	0
Extensions and discoveries	65,992	43,469	54,664
Property sales	0	0	(126,600)
Production	(23,907)	(23,989)	(22,657)
Purchase of reserves in place	8,351	25,394	37,200
Proved developed and undeveloped reserves, End of year	534,279	630,192	632,178
Proved developed reserves (volume), Beginning of year	268,566	255,520	361,575
Proved developed reserves (volume), End of year	221,606	268,566	255,520