Acquisitions and Dispositions (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended			3 Months Ended	12 Months Ended
	Oct. 31, 2011	Nov. 30, 2009 acre	Aug. 31, 2008	Jun. 30, 2011	Dec. 31, 2012	Dec. 31, 2010
Acquisitions and Dispositions [Abstract]
Sale Proceeds from disposal of Properties	$ 48.8		$ 15.0	$ 15.0
Purchase price adjustment related to the property disposal	4.7
Buyer's assumption of asset retirement obligation					27.7
Percentage of leased working interest		50.00%
Percentage of retained working interest		50.00%
Area of percentage of leased working interest		26,000
Amount received from leasing		26
Consideration for future capital expenditures						$ 13