Derivatives (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) contracts	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) contracts	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Credit Derivatives [Line Items]
Counterparty default losses on forward contracts	$ 0	$ 0	$ 0	$ 0
Commitments and contingent liabilities
Number of interest rate derivatives held | contracts	354		354
Termination value of derivatives in net liability position	$ 48,400,000		$ 48,400,000		$ 29,000,000
CollateralPostingClearing	66,700,000		66,700,000		$ 43,500,000
Decrease in settlement values of the Bank's derivative assets	(2,500,000)		(2,500,000)
Interest Rate Swap [Member]
Credit Derivatives [Line Items]
Notional amount of credit risk derivatives	1,700,000,000		1,700,000,000
Interest Rate Forward Sales Commitments [Member]
Credit Derivatives [Line Items]
Commitments and contingent liabilities	601,060,000		601,060,000
Commitments To Originate Loans Held For Sale [Member]
Credit Derivatives [Line Items]
Commitments and contingent liabilities	$ 402,051,000		$ 402,051,000