Derivative Financial Instruments Fair Value (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Fair value of derivative assets and liabilities
Price Risk Derivatives, at Fair Value, Net	$ 21,500,000	$ 38,700,000
Derivative Assets, Current	21,559,000	37,873,000
Derivative Liabilities, Current	26,380,000	8,999,000
Derivative Assets, Noncurrent	30,951,000	16,466,000
Derivative Liabilities, Noncurrent	4,640,000	6,645,000
Derivative Asset, Fair Value, Amount Offset Against Collateral	52,510,000	54,339,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(30,652,000)	(13,400,000)
Derivative Asset, Fair Value, Amount Offset Against Collateral, Net	21,858,000	40,939,000
Derivative Liability, Fair Value, Amount Offset Against Collateral	(31,020,000)	(15,644,000)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	30,652,000	13,400,000
Derivative Liability, Fair Value, Amount Offset Against Collateral, Net	(368,000)	(2,244,000)
Not Designated as Hedging Instrument [Member]
Fair value of derivative assets and liabilities
Derivative Assets, Current	21,559,000	37,873,000
Derivative Liabilities, Current	26,380,000	8,999,000
Derivative Assets, Noncurrent	30,951,000	16,466,000
Derivative Liabilities, Noncurrent	4,640,000	6,645,000
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Not Designated as Hedging Instrument [Member]
Fair value of derivative assets and liabilities
Fair Value: Derivative Assets	52,510,000	54,339,000
Fair Value: Derivative Liabilities	$ 31,020,000	$ 15,644,000