Derivatives (Derivatives Associated with Fixed Income Trading Activities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Customer Interest Rate Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	$ 2,026,753	$ 1,697,992
Assets	22,097	39,495
Liabilities	18,323	14,996
Offsetting Upstream Interest Rate Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	2,026,753	1,697,992
Assets	17,931	14,996
Liabilities	20,720	39,495
Option Contracts Purchased \| Short
Derivative Instruments, Gain (Loss) [Line Items]
Notional		5,000
Assets		0
Liabilities		8
Option Contracts Purchased \| Long
Derivative Instruments, Gain (Loss) [Line Items]
Notional	20,000	17,500
Assets	15	63
Liabilities	0	0
Forwards and Futures Purchased
Derivative Instruments, Gain (Loss) [Line Items]
Notional	6,257,140	2,916,750
Assets	4,354	6,257
Liabilities	5,526	26,659
Forwards and Futures Sold
Derivative Instruments, Gain (Loss) [Line Items]
Notional	6,292,012	3,085,396
Assets	5,806	27,330
Liabilities	$ 4,010	$ 6,615

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611

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Fair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities.

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