Property and Equipment (Narr) (Cap & Impair) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property, Plant and Equipment [Line Items]
Impairment of oil and gas properties	$ 6,000	$ 11,400	$ 20,000	$ 15,700	$ 36,900	$ 28,800	$ 0	$ 0	$ 53,072	$ 65,706	$ 7,692
[CurrentYearMember]
Property, Plant and Equipment [Line Items]
Impairment of oil and gas properties									53,100
[CurrentYearMember] | [CapitalizedEmployeesCostsMember]
Property, Plant and Equipment [Line Items]
Oil and Gas Property, Full Cost Method, Gross	17,900								17,900
[CurrentYearMember] | [CapitalizedInterestCostsMember]
Property, Plant and Equipment [Line Items]
Interest Costs Capitalized									26,900
[OneYearPriorMember]
Property, Plant and Equipment [Line Items]
Impairment of oil and gas properties									65,700
[OneYearPriorMember] | [CapitalizedEmployeesCostsMember]
Property, Plant and Equipment [Line Items]
Oil and Gas Property, Full Cost Method, Gross	13,300								13,300
[OneYearPriorMember] | [CapitalizedInterestCostsMember]
Property, Plant and Equipment [Line Items]
Interest Costs Capitalized									14,700
[TwoYearPriorMember]
Property, Plant and Equipment [Line Items]
Impairment of oil and gas properties									7,700
[TwoYearPriorMember] | [CapitalizedEmployeesCostsMember]
Property, Plant and Equipment [Line Items]
Oil and Gas Property, Full Cost Method, Gross	13,100								13,100
[TwoYearPriorMember] | [CapitalizedInterestCostsMember]
Property, Plant and Equipment [Line Items]
Interest Costs Capitalized									$ 3,900