Natural Gas And Oil Properties (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Period of time needed to calculate ceiling value of reserves	12 months
Discount rate of natural gas and oil reserves	10.00%
Cash flow hedges impact on ceiling value, net of tax	$ 14.0	$ 79.0
Henry Hub Natural Gas [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Period of time needed to calculate ceiling value of reserves	12 months	12 months
Full cost ceiling test, price	4.24	3.60
West Texas Intermediate Oil [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Period of time needed to calculate ceiling value of reserves	12 months	12 months
Full cost ceiling test, price	95.56	91.56