Derivatives (Derivatives Associated With Interest Rate Risk Management Activities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Customer Interest Rate Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	$ 2,022,577	$ 2,026,753
Assets	12,228	22,097
Liabilities	40,742	18,323
Offsetting Upstream Interest Rate Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	2,022,577	2,026,753
Assets	39,429	17,931
Liabilities	11,677	20,720
Customer Interest Rate Contracts Hedging | Hedging Instruments And Hedged Items | Customer Interest Rate Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	1,759,979	1,608,912
Assets	6,214	11,644
Liabilities	38,335	19,780
Customer Interest Rate Contracts Hedging | Hedging Instruments And Hedged Items | Offsetting Upstream Interest Rate Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	1,759,979	1,608,912
Assets	36,050	18,473
Liabilities	6,339	11,019
Debt Hedging | Hedging Instruments And Hedged Items | Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional	900,000	900,000
Assets		371
Liabilities	57
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	(20,023)	(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	(3,506)	(3,910)
Debt Hedging | Hedging Instruments And Hedged Items | Term Borrowings
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings	$ 876,471	$ 882,618