Derivative Financial Instruments Fair Value (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Fair value of derivative assets and liabilities
Derivative asset	$ 58,071	$ 37,873
Derivative asset	28,798	16,466
Derivative liability	4,748	8,999
Derivatives liability	1,525	6,645
Derivative Asset, Fair Value, Amount Offset Against Collateral	86,869	54,339
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(6,273)	(13,400)
Derivative Asset, Fair Value, Amount Offset Against Collateral, Net	80,596	40,939
Derivative Liability, Fair Value, Amount Offset Against Collateral	(6,273)	(15,644)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	6,273	13,400
Derivative Liability, Fair Value, Amount Offset Against Collateral, Net	0	(2,244)
Derivatives not designated as hedging instruments
Fair value of derivative assets and liabilities
Derivative asset	58,071	37,873
Derivative asset	28,798	16,466
Derivative liability	4,748	8,999
Derivatives liability	1,525	6,645
Level 2 | Derivatives not designated as hedging instruments | Fair Value, Measurements, Recurring [Member]
Fair value of derivative assets and liabilities
Derivative assets not designated as hedging instruments	86,869	54,339
Derivative liabilities not designated as hedging instruments	$ 6,273	$ 15,644