Derivatives (Derivatives Associated with Fixed Income Trading 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
Put Option | Long
Derivative Instruments, Gain (Loss) [Line Items]
Notional	10,000	20,000
Assets	13	15
Liabilities	0	0
Forwards And Futures Purchased
Derivative Instruments, Gain (Loss) [Line Items]
Notional	6,019,851	6,257,140
Assets	10,429	4,354
Liabilities	8,757	5,526
Forwards And Futures Sold
Derivative Instruments, Gain (Loss) [Line Items]
Notional	6,212,589	6,292,012
Assets	9,062	5,806
Liabilities	$ 9,801	$ 4,010