Derivative Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011 Natural Gas [Member] MMcf	Dec. 31, 2011 Oil [Member] MMBbls	Mar. 31, 2012 Commodity Contracts [Member]	Mar. 31, 2011 Commodity Contracts [Member]	Mar. 31, 2012 Remainder Of 2012 [Member] Natural Gas [Member]	Mar. 21, 2012 Remainder Of 2012 [Member] Oil [Member]	Mar. 31, 2012 2013 [Member] Natural Gas [Member]	Mar. 21, 2012 2013 [Member] Oil [Member]
Derivative [Line Items]
Unrealized fair value adjustments included in "Gain (loss) on derivative financial instruments"					$ 3.7	$ (23.5)
Outstanding derivative contracts volume			85,995	275
Average forward prices							2.50	104.54	3.47	103.59
Percentage of derivative instruments to equivalent production	42.40%	54.70%