Dispositions (Details) (USD $)	1 Months Ended	3 Months Ended	9 Months Ended			1 Months Ended	9 Months Ended	6 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended
	Mar. 31, 2010	Sep. 30, 2011	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Mar. 31, 2010 Ohio Properties [Member]	Sep. 30, 2010 Ohio Properties [Member]	Jun. 30, 2011 Barnett Shale Properties [Member]	Sep. 30, 2011 Barnett Shale Properties [Member]	Sep. 30, 2011 East Texas [Member]	Sep. 30, 2011 East Texas [Member]	Sep. 30, 2011 Pennsylvania [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from the sale of natural gas properties									$ 889,300,000
Gain or loss on sale of natural gas properties									4,900,000
Loss on derivative contracts								(1,700,000)
Gain from sale of oil and gas properties							77,400,000
Proceeds from sale of oil and gas properties			66,213,000	327,454,000			323,000,000			11,000,000	11,000,000	6,000,000
Loss (gain) on sale of assets			(1,280,000)	78,156,000
Impairment on Oil and Gas Properties		38,681,000	38,681,000	6,505,000						31,200,000		0
Proceeds used to repay outstanding borrowings under credit facility			764,826,000	943,000,000			135,000,000
Percentage of sale closed	90.00%					90.00%
Accumulated other comprehensive income (loss)		$ 86,209,000	$ 86,209,000		$ 67,470,000				$ 9,400,000