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Derivatives, Derivatives Instruments Gain (Loss) in Income Statement (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	$ 14,639	$ 9,817	$ 32,477	$ 39,110
Gain (Loss) on Derivatives, Net	(2,847)	1,033	(11,589)	3,824
To-be-announced residential mortgage-backed securities [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	7,272	9,181	21,677	26,413
Gain (Loss) on Derivatives, Net	0	0	0	0
Interest rate swaps [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	618	767	2,057	1,891
Gain (Loss) on Derivatives, Net	0	0	0	0
Energy contracts [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	541	378	5,097	4,917
Gain (Loss) on Derivatives, Net	0	0	0	0
Agricultural contracts [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	6	38	36	58
Gain (Loss) on Derivatives, Net	0	0	0	0
Foreign exchange contracts [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	78	164	350	524
Gain (Loss) on Derivatives, Net	0	0	0	0
Equity option contracts [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	0	0	0	0
Gain (Loss) on Derivatives, Net	0	0	0	0
Total customer risk management programs
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	8,515	10,528	29,217	33,803
Gain (Loss) on Derivatives, Net	0	0	0	0
Internal risk management programs [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Brokergage and Trading Revenue	6,124	(711)	3,260	5,307
Gain (Loss) on Derivatives, Net	$ (2,847)	$ 1,033	$ (11,589)	$ 3,824

X

- Definition

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
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- Definition

Amount of gain (loss) resulting from the difference between the acquisition price and the selling price or fair value of trading assets and trading liabilities, conducted separately from customer trading activities. Includes, but is not limited to, changes in fair value of trading assets and trading liabilities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4F
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-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624186-113959

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 320
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-Publisher FASB
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