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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 | 6 Months Ended
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Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract] |  |  |  |
Brokergage and Trading Revenue | $ 8,815 | $ 18,122 | $ 17,838 | $ 29,293
Gain (Loss) on Derivatives, Net | (3,057) | 3,241 | (8,742) | 2,791
To-be-announced residential mortgage-backed securities |  |  |  |
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract] |  |  |  |
Brokergage and Trading Revenue | 7,586 | 9,205 | 14,405 | 17,232
Gain (Loss) on Derivatives, Net | 0 | 0 | 0 | 0
Interest rate swaps |  |  |  |
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract] |  |  |  |
Brokergage and Trading Revenue | 683 | 665 | 1,439 | 1,124
Gain (Loss) on Derivatives, Net | 0 | 0 | 0 | 0
Energy contracts |  |  |  |
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract] |  |  |  |
Brokergage and Trading Revenue | 1,416 | 1,666 | 4,556 | 4,539
Gain (Loss) on Derivatives, Net | 0 | 0 | 0 | 0
Agricultural contracts |  |  |  |
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract] |  |  |  |
Brokergage and Trading Revenue | 15 | 11 | 30 | 20
Gain (Loss) on Derivatives, Net | 0 | 0 | 0 | 0
Foreign exchange contracts |  |  |  |
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract] |  |  |  |
Brokergage and Trading Revenue | 96 | 90 | 272 | 360
Gain (Loss) on Derivatives, Net | 0 | 0 | 0 | 0
Equity option contracts |  |  |  |
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 | 9,796 | 11,637 | 20,702 | 23,275
Gain (Loss) on Derivatives, Net | 0 | 0 | 0 | 0
Internal risk management programs |  |  |  |
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract] |  |  |  |
Brokergage and Trading Revenue | (981) | 6,485 | (2,864) | 6,018
Gain (Loss) on Derivatives, Net | $ (3,057) | $ 3,241 | $ (8,742) | $ 2,791

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- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a),(c),(d),(e) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959 + Details
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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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.13(e)) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -Section 35 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=35711043&loc=d3e42454-110968 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42567-110969 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4F -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624186-113959 + Details
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