Derivative Financial Instruments Fair Value (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013
Fair value of derivative assets and liabilities
Derivative, Fair Value, Net	$ 592,100,000		$ 21,500,000
Derivative Assets, Current	402,668,000		21,559,000
Derivative Liabilities, Current	0		26,380,000
Derivative Assets, Noncurrent	189,540,000		30,951,000
Derivative Liabilities, Noncurrent	70,000		4,640,000
Derivative Asset, Fair Value, Gross Asset	592,208,000		52,510,000
Derivative Liability, Fair Value, Gross Liability	(70,000)		(31,020,000)
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	70,000		30,652,000
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	70,000		30,652,000
Derivative Asset, Fair Value, Amount Offset Against Collateral, Net	592,138,000		21,858,000
Derivative Liability, Fair Value, Amount Offset Against Collateral, Net	0		(368,000)
Not Designated as Hedging Instrument [Member]
Fair value of derivative assets and liabilities
Derivative Assets, Current	402,668,000		21,559,000
Derivative Liabilities, Current	0		26,380,000
Derivative Assets, Noncurrent	189,540,000		30,951,000
Derivative Liabilities, Noncurrent	70,000		4,640,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Not Designated as Hedging Instrument [Member]
Fair value of derivative assets and liabilities
Derivative Asset, Fair Value, Gross Asset	592,208,000	[1]	52,510,000	[1]
Derivative Liability, Fair Value, Gross Liability	$ 70,000	[1]	$ 31,020,000	[1]

[1] (1) This represents a financial asset or liability that is measured at fair value on a recurring basis.