Derivatives (Narrative) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) contracts	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) contracts	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) contracts
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	592		592		516
Termination value of derivatives in net liability position	$ 4,300,000		$ 4,300,000		$ 34,900,000
Collateral posting clearing	34,400,000		34,400,000		50,300,000
Variation Margin Payment	32,600,000		32,600,000
Decrease in settlement values of the Bank's derivative assets	1,700,000		1,700,000		241,000
Interest Rate Swap
Credit Derivatives [Line Items]
Notional amount of credit risk derivatives	2,700,000,000		2,700,000,000		$ 2,300,000,000
Commitments To Originate Loans Held For Sale
Credit Derivatives [Line Items]
Commitments and contingent liabilities	450,644,000		450,644,000
Interest Rate Forward Sales Commitments
Credit Derivatives [Line Items]
Commitments and contingent liabilities	$ 672,175,000		$ 672,175,000