Derivatives (Narrative) (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) contracts	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) contracts	Jun. 30, 2018 USD ($)	Dec. 31, 2018 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
Termination value of derivatives in net liability position	5,500		5,500		12,700
Collateral posting clearing	58,500		58,500		36,900
Variation Margin Payment	(142,700)		(142,700)		(32,500)
Derivative Credit Risk Valuation Adjustment, Change In Derivative Assets	$ (9,400)		$ (9,400)		$ (3,000)
Interest Rate Swap
Credit Derivatives [Line Items]
Number of interest rate derivatives held | contracts	785		785		767
Notional amount of credit risk derivatives	$ 4,600,000		$ 4,600,000		$ 4,200,000
Commitments To Originate Loans Held For Sale
Credit Derivatives [Line Items]
Commitments and contingent liabilities	292,216		292,216
Interest Rate Forward Sales Commitments
Credit Derivatives [Line Items]
Commitments and contingent liabilities	$ 553,648		$ 553,648