Derivative Financial Instruments - Gain (Loss) Recognized (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivative instruments not designated as hedging instruments \| Trading revenues, net
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments	$ 110,567	$ 90,718	$ 253,761
Derivative instruments not designated as hedging instruments \| Foreign currency, Futures contracts \| Trading revenues, net
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments	4,273	10,535	12,191
Derivative instruments not designated as hedging instruments \| Foreign currency, Forward contracts \| Investment income and other, net
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments	(10)	526	0
Derivative instruments not designated as hedging instruments \| Equity, Futures contracts \| Trading revenues, net
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments	30,479	25,247	50,073
Derivative instruments not designated as hedging instruments \| Equity, Swap contracts \| Trading revenues, net
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments	3,789	5,277	11,736
Derivative instruments not designated as hedging instruments \| Equity, Listed options \| Trading revenues, net
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments	(14,278)	(37,439)	37,035
Derivative instruments not designated as hedging instruments \| Fixed income, Futures contracts \| Trading revenues, net
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments	37,710	31,277	80,511
Derivative instruments not designated as hedging instruments \| Commodity, Futures contracts \| Trading revenues, net
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments	48,604	55,295	62,215
Derivative instruments designated as hedging instruments \| Foreign currency, Forward contracts \| Accumulated other comprehensive income
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments designated as hedging instruments	$ 208	$ 0	$ (3,298)

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- Definition

The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959

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- Definition

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959

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