Derivatives (Narrative) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) contracts	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) contracts	Sep. 30, 2018 USD ($)	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
Termination value of derivatives in a net liability position	4,000		4,000		12,700
Collateral required to be posted under agreements	84,300		84,300		36,900
Variation Margin Adjustment	(199,200)		(199,200)		(32,500)
Decrease in settlement values of net derivative assets	$ (14,000)		$ (14,000)		$ (3,000)
Interest Rate Swap [Member]
Credit Derivatives [Line Items]
Number of interest rate swaps | contracts	824		824		767
Derivative, Notional Amount	$ 5,400,000		$ 5,400,000		$ 4,200,000
Commitments To Originate Loans Held For Sale
Credit Derivatives [Line Items]
Commitments	421,515		421,515
Interest rate forward sales commitments
Credit Derivatives [Line Items]
Commitments	$ 637,954		$ 637,954