Derivatives (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013 contracts	Sep. 30, 2012	Sep. 30, 2013 contracts	Sep. 30, 2012	Dec. 31, 2012
Credit Derivatives [Line Items]
Counterparty default losses on forward contracts	$ 0	$ 0	$ 0	$ 0
Commitments and contingent liabilities
Number of interest rate derivatives held	239		239
Notional amount of credit risk derivatives	1,200,000,000		1,200,000,000
Termination value of derivatives in net liability position	12,000,000		12,000,000
CollateralPostingClearing	10,400,000		10,400,000
Minimum collateral posting agreement amount	3,300,000		3,300,000
Decrease in settlement values of the Bank's derivative assets	1,200,000		1,200,000
Gain (loss) on nonhedge derivative instruments related to credit valuation adjustments	(700,000)	235,000	1,100,000	352,000
Interest Rate Forward Sales Commitments [Member]
Credit Derivatives [Line Items]
Commitments and contingent liabilities	184,576,000		184,576,000
Commitments To Originate Loans Held For Sale [Member]
Credit Derivatives [Line Items]
Commitments and contingent liabilities	$ 112,421,000		$ 112,421,000