Derivatives (Narrative) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) contracts	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) contracts	Sep. 30, 2017 USD ($)	Dec. 31, 2017 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	741		741		653
Termination value of derivatives in net liability position	$ 39,300		$ 39,300		$ 7,200
Collateral posting clearing	36,500		36,500		28,200
Variation Margin Payment	28,400		28,400		(20,500)
Derivative Credit Risk Valuation Adjustment, Change In Derivative Assets	16		16		(1,700)
Interest Rate Swap
Credit Derivatives [Line Items]
Notional amount of credit risk derivatives	3,900,000		3,900,000		$ 3,000,000
Commitments To Originate Loans Held For Sale
Credit Derivatives [Line Items]
Commitments and contingent liabilities	265,577		265,577
Interest Rate Forward Sales Commitments
Credit Derivatives [Line Items]
Commitments and contingent liabilities	$ 484,466		$ 484,466