Derivatives (Derivatives Associated With Interest Rate Risk Management Activities) (Details) - USD ($) $ in Thousands		Jun. 30, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings		$ 1,033,329	$ 1,040,656
Customer Interest Rate Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional		1,903,647	1,697,992
Assets		34,224	39,495
Liabilities		12,508	14,996
Offsetting Upstream Interest Rate Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional		1,903,647	1,697,992
Assets		12,368	14,996
Liabilities		31,374	39,495
Customer Interest Rate Contracts Hedging | Hedging Instruments And Hedged Items | Customer Interest Rate Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional		1,513,114	1,357,920
Assets		17,056	17,566
Liabilities		12,944	14,277
Customer Interest Rate Contracts Hedging | Hedging Instruments And Hedged Items | Offsetting Upstream Interest Rate Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional		1,513,114	1,357,920
Assets		11,878	14,277
Liabilities		15,630	18,066
Debt Hedging | Hedging Instruments | Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional		900,000	900,000
Assets			1,628
Liabilities		796	7,276
Debt Hedging | Hedged Items | Term Borrowings
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings	[1]	$ 900,000	$ 900,000

[1] Represents par value of term borrowings being hedged.