Derivatives (Derivatives Associated With Interest Rate Risk Management Activities) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Customer Interest Rate Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	$ 1,954,439	$ 1,697,992
Assets	30,564	39,495
Liabilities	12,256	14,996
Offsetting Upstream Interest Rate Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	1,954,439	1,697,992
Assets	12,119	14,996
Liabilities	28,012	39,495
Customer Interest Rate Contracts Hedging | Hedging Instruments And Hedged Items | Customer Interest Rate Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	1,540,036	1,357,920
Assets	16,607	17,566
Liabilities	12,675	14,277
Customer Interest Rate Contracts Hedging | Hedging Instruments And Hedged Items | Offsetting Upstream Interest Rate Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	1,540,036	1,357,920
Assets	11,612	14,277
Liabilities	15,350	18,066
Debt Hedging | Hedging Instruments And Hedged Items | Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional	900,000	900,000
Assets		1,628
Liabilities	779	7,276
Debt Hedging | Hedging Instruments And Hedged Items | Term Borrowings
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings	$ 900,000	$ 900,000