Subsequent Event (Strat, Fwd Sale, Reimburse) (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended
	Feb. 28, 2013 bbl	Dec. 31, 2012
Subsequent Event [Line Items]
Subsequent Event Month		March 2013
Subsequent Event, Description		In January 2013, we entered into the Procurement Agreement with an unaffiliated third party entity, which matures on July 9, 2014. The Procurement Agreement was entered into in connection with the unaffiliated third party’s entry into a credit support arrangement with a providing bank. Pursuant to this credit support arrangement, the third party pledged cash, contributed by one of our shareholders, to secure letters of credit in the amount of $33.0 million. The letters of credit secure decommissioning obligations in connection with certain of our U.K. license agreements.
[ForwardSaleMember] | [UnitedKingdomNorthSeaMember]
Subsequent Event [Line Items]
Subsequent Event, Date	Feb. 01, 2013	Mar. 01, 2013
Deferred Revenue	$ 22.5
Oil and Gas Delivery Commitments and Contracts, Remaining Contractual Volume	200,000
[StrategicAlternativesMember]
Subsequent Event [Line Items]
Subsequent Event, Date		Feb. 14, 2013