Property and Equipment (Details Textuals) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Property and Equipment (Textuals) [Abstract]
Cost incurred on proved reserves transferred to amortization base	$ 51.2
Description of Current Status of Project	Exploration and development costs shown as unevaluated properties are primarily associated with our tertiary oil fields that are under development but did not have proved reserves at December 31, 2011. The most significant of these costs during 2011 related to Oyster Bayou and Hastings Fields, for which we have initiated CO2 floods but have not yet recognized proved reserves. Our 2010 property acquisition costs were primarily related to the fair value allocated to CO2 tertiary potential at our Bell Creek and Cedar Creek Anticline properties and the undeveloped potential assigned to our Bakken properties, all acquired as part of the Encore Merger. Our 2009 property acquisition costs were primarily related to CO2 tertiary potential at our Conroe Field. Property acquisition costs for 2008 and prior were primarily for CO2 tertiary potential at Oyster Bayou.
Anticipated Timing of Inclusion of Costs in Amortization Calculation	We currently estimate that evaluation of most of these properties and the inclusion of their costs in the amortization base is expected to be completed within five years.