Derivatives and Hedging Activities (Credit Risk Exposure) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Derivative [Line Items]
Credit risk exposure	$ 53,452	[1]	$ 44,544	[1]
Derivative assets	25,394		36,256
Accrued interest receivable	120,715		132,152
Net exposure after collateral	24,053		36,256
Derivative Financial Instruments, Assets [Member]
Derivative [Line Items]
Accrued interest receivable	9,500		3,100
Cash Collateral And Related Accrued Interest [Member]
Derivative [Line Items]
Cash collateral	(28,058)		(8,288)
Other Collateral held	$ 1,341		$ 0

[1] Includes net accrued interest receivable of $9.5 million and $3.1 million at September 30, 2012 and December 31, 2011, respectively.