Derivative Instruments Derivative Instruments (Details 3) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Derivative [Line Items]
Collateral Already Posted, Aggregate Fair Value	$ 26,300,000	$ 11,200,000
Derviative Instrument by Counterparty, Gross Amount Recognized on Balance Sheet [Member]
Derivative [Line Items]
Derivative Assets	(15,300,000)	(15,300,000)
Derivative Liabilities	(38,700,000)	(12,500,000)
Derviative Instrument by Counterparty, Gross Amount Not Offset on Balance Sheet [Member] [Member]
Derivative [Line Items]
Collateral Already Posted, Aggregate Fair Value	3,900,000	10,300,000
Derivative Assets	(4,900,000)	(400,000)
Derivative Liabilities	(8,900,000)	(11,500,000)
Derviative Instrument by Counterparty, Net Amount [Member]
Derivative [Line Items]
Derivative Assets	(10,400,000)	(14,900,000)
Derivative Liabilities	$ (29,800,000)	$ (1,000,000)