Derivatives (Derivatives Associated With Interest Rate Risk Management Activities) (Details) - USD ($) $ in Thousands		Mar. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings		$ 1,035,036	$ 1,040,656
Customer Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional		1,743,855	1,697,992
Assets		34,060	39,495
Liabilities		15,510	14,996
Offsetting Upstream Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional		1,743,855	1,697,992
Assets		15,258	14,996
Liabilities		31,677	39,495
Customer Interest Rate Contracts Hedging [Member] | Hedging Instruments And Hedged Items [Member] | Customer Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional		1,450,711	1,357,920
Assets		15,401	17,566
Liabilities		15,388	14,277
Customer Interest Rate Contracts Hedging [Member] | Hedging Instruments And Hedged Items [Member] | Offsetting Upstream Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional		1,450,711	1,357,920
Assets		14,053	14,277
Liabilities		14,277	18,066
Debt Hedging [Member] | Hedging Instruments [Member] | Interest Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional		900,000	900,000
Assets		749	1,628
Liabilities			7,276
Debt Hedging [Member] | Hedged Items [Member] | Term Borrowings [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings	[1]	$ 900,000	$ 900,000

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