Derivatives (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) contracts	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) contracts	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) contracts
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Counterparty default losses on forward contracts	$ 0	$ 0	$ 0	$ 0
Credit Derivatives [Line Items]
Commitments and contingent liabilities
Number of interest rate derivatives held | contracts	613		613		516
Termination value of derivatives in net liability position	$ 4,400,000		$ 4,400,000		$ 34,900,000
Collateral posting clearing	32,000,000		32,000,000		50,300,000
Variation Margin Payment	32,700,000		32,700,000
Decrease in settlement values of the Bank's derivative assets	1,900,000		1,900,000		241,000
Interest Rate Swap
Credit Derivatives [Line Items]
Notional amount of credit risk derivatives	2,800,000,000		2,800,000,000		$ 2,300,000,000
Commitments To Originate Loans Held For Sale
Credit Derivatives [Line Items]
Commitments and contingent liabilities	405,786,000		405,786,000
Interest Rate Forward Sales Commitments
Credit Derivatives [Line Items]
Commitments and contingent liabilities	$ 625,308,000		$ 625,308,000