Derivatives and Hedging Activities Offsetting of Derivative Assets and Derivative Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Offsetting [Abstract]
Derivative Asset With Legal Right of Offset, Fair Value, Gross Asset	$ 59,113	$ 69,522
Derivative Liability With Legal Right of Offset, Fair Value, Gross Liability	342,637	388,889
Derivative Asset, Collateral, Obligation to Return Cash, Offset	(54,402)	(63,800)
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	(234,066)	(274,585)
Derivative Asset, Net Amounts After Offsetting Adjustment, Fair Value	4,711	5,722
Derivative Liability, Net Amounts After Offsetting Adjustment, Fair Value	108,571	114,304
Derivative Asset, Not Subject to Master Netting Arrangement	123	155
Derivative Liability, Not Subject to Master Netting Arrangement	359	584
Derivative assets	4,834	5,877
Derivative liabilities	$ 108,930	$ 114,888