Oil And Gas Properties (Narrative) (Details) (USD $)	1 Months Ended		3 Months Ended											12 Months Ended								3 Months Ended	6 Months Ended	12 Months Ended			1 Months Ended		3 Months Ended	12 Months Ended
	Feb. 28, 2010	Aug. 31, 2006	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Sep. 30, 2009	Jun. 30, 2009	Mar. 31, 2009	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009		Dec. 31, 2007	Feb. 28, 2009	Dec. 31, 2011 United Kingdom [Member]	Jun. 30, 2010 United Kingdom [Member]	Dec. 31, 2011 United Kingdom [Member]		Dec. 31, 2010 United Kingdom [Member]	Feb. 28, 2010 Camelot Field [Member]	Dec. 31, 2011 Camelot Field [Member]	Jun. 30, 2009 Hurricane [Member]	Dec. 31, 2009 Hurricane [Member]	Dec. 31, 2011 Gulf Of Mexico Oil And Gas Properties [Member]	Dec. 31, 2010 Non Producing Oil Field [Member]	Dec. 31, 2011 Producing Oil Field [Member]	Dec. 31, 2010 Producing Oil Field [Member]	Dec. 31, 2009 Producing Oil Field [Member]
Oil And Gas Properties [Line Items]
Capitalized exploration cost			$ 5,800,000											$ 5,800,000
Royalty Payments To US Government														85,400,000		37,200,000		26,800,000
Acquired working interest	50.00%	100.00%												50.00%													50.00%
Working interest in oil and gas field, sold																				30.00%
Working interest in oil and gas field																50.00%		25.00%		100.00%
Cash payment for development of fields														126,196,000	[1]	53,002,000	[1]	71,489,000	[1]						[1]
Proceeds from sales of property												800,000	18,000,000	31,000,000						40,000,000
Proceeds from sale of oil and gas property												800,000	18,000,000	31,000,000						40,000,000
Gain (loss) on sale of oil and gas property												1,200,000		4,500,000
Leasehold interests (in percentage)																		100.00%
Partner paid drilling costs to evaluate prospective (in percentage)																		100.00%
Accrued royalties																					73,500,000
Additional royalties interest (in percentage)													5.00%
Impairment charges																															112,600,000
Increase in expected asset retirement cost			28,200,000											20,000,000								15,900,000
Oil and gas property impairments			107,500,000	2,400,000	22,700,000	0	9,200,000	900,000	159,900,000	11,100,000	64,600,000	48,200,000		132,603,000		181,083,000		120,550,000					5,000,000	20,000,000		5,000,000			43,800,000	51,500,000	21,700,000	3,500,000	90,900,000	172,600,000	72,400,000
Asset retirement obligation			$ 254,391,000				$ 234,936,000							$ 254,391,000		$ 234,936,000		$ 248,128,000										$ 27,300,000

[1] Development costs include costs incurred to obtain access to proved reserves to drill and equip development wells. Development costs also include costs of developmental dry holes.