Derivatives (Derivatives Associated with Fixed Income Trading Activities) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Customer interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	$ 2,204,706	$ 2,026,753
Assets	9,837	22,097
Liabilities	48,272	18,323
Offsetting upstream interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	2,204,706	2,026,753
Assets	46,619	17,931
Liabilities	9,676	20,720
Option contracts purchased \| Long
Derivative Instruments, Gain (Loss) [Line Items]
Notional	70,000	20,000
Assets	58	15
Liabilities	0	0
Forwards and futures purchased
Derivative Instruments, Gain (Loss) [Line Items]
Notional	5,466,761	6,257,140
Assets	16,942	4,354
Liabilities	1,902	5,526
Forwards and futures sold
Derivative Instruments, Gain (Loss) [Line Items]
Notional	5,556,237	6,292,012
Assets	2,185	5,806
Liabilities	$ 16,836	$ 4,010

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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