Derivatives (Derivatives Associated With Interest Rate Risk Management Activities) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Customer interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	$ 2,204,706	$ 2,026,753
Assets	9,837	22,097
Liabilities	48,272	18,323
Offsetting upstream interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	2,204,706	2,026,753
Assets	46,619	17,931
Liabilities	9,676	20,720
Customer Interest Rate Contracts Hedging | Hedging Instruments And Hedged Items | Customer interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	1,843,573	1,608,912
Assets	6,180	11,644
Liabilities	42,760	19,780
Customer Interest Rate Contracts Hedging | Hedging Instruments And Hedged Items | Offsetting upstream interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	1,843,573	1,608,912
Assets	40,026	18,473
Liabilities	6,383	11,019
Debt Hedging | Hedging Instruments And Hedged Items | Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Notional	900,000	900,000
Assets	22	371
Liabilities	4
Debt Hedging | Hedging Instruments And Hedged Items | Term borrowings, Par
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings	900,000	900,000
Debt Hedging | Hedging Instruments And Hedged Items | Term borrowings, Cumulative fair value hedging adjustments
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings	(21,542)	(13,472)
Debt Hedging | Hedging Instruments And Hedged Items | Term borrowings, Unamortized premium/(discount) and issuance costs
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings	(3,103)	(3,910)
Debt Hedging | Hedging Instruments And Hedged Items | Total carrying value
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings	$ 875,355	$ 882,618