Derivative Instruments - Fair Value of Derivative Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Equities futures \| Receivables from broker dealers and clearing organizations
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	$ (569)	$ (1,017)
Derivatives Assets, Notional	294,910	617,398
Equities futures \| Payables to broker dealers and clearing organizations
Fair value of derivative instruments on a gross basis
Derivatives Liabilities, Fair Value	(3,151)	202
Derivatives Liabilities, Notional	369,368	75,428
Commodity futures \| Receivables from broker dealers and clearing organizations
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	(17)	(8,431)
Derivatives Assets, Notional	146,063	18,635,531
Commodity futures \| Payables to broker dealers and clearing organizations
Fair value of derivative instruments on a gross basis
Derivatives Liabilities, Fair Value	110,272	585
Derivatives Liabilities, Notional	19,325,868	25,932
Currency futures \| Receivables from broker dealers and clearing organizations
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	39,140	1,358
Derivatives Assets, Notional	3,362,827	3,059,575
Currency futures \| Payables to broker dealers and clearing organizations
Fair value of derivative instruments on a gross basis
Derivatives Liabilities, Fair Value	(5,606)	(12,475)
Derivatives Liabilities, Notional	1,806,592	2,570,005
Fixed Income futures \| Receivables from broker dealers and clearing organizations
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	22	30
Derivatives Assets, Notional	91,167	232,473
Fixed Income futures \| Payables to broker dealers and clearing organizations
Fair value of derivative instruments on a gross basis
Derivatives Liabilities, Fair Value	(6)
Derivatives Liabilities, Notional	104,997
Options
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	220	168
Derivatives Liabilities, Fair Value	211	163
Options \| Receivables from broker dealers and clearing organizations
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	220	168
Derivatives Assets, Notional	8,112	24,453
Options \| Financial instruments sold, not yet purchased
Fair value of derivative instruments on a gross basis
Derivatives Liabilities, Fair Value	211	163
Derivatives Liabilities, Notional	8,140	1
Currency forwards
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	1,398,720	795,435
Derivatives Liabilities, Fair Value	1,457,967	746,014
Currency forwards \| Financial instruments owned
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	1,398,720	795,435
Derivatives Assets, Notional	77,896,379	69,614,513
Currency forwards \| Financial instruments sold, not yet purchased
Fair value of derivative instruments on a gross basis
Derivatives Liabilities, Fair Value	1,457,967	746,014
Derivatives Liabilities, Notional	80,537,570	71,019,047
Interest rate swaps
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	351
Derivatives Liabilities, Fair Value	357	319
Interest rate swaps \| Financial instruments owned
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	351	311
Derivatives Assets, Notional	82,010	82,010
Interest rate swaps \| Financial instruments sold, not yet purchased
Fair value of derivative instruments on a gross basis
Derivatives Liabilities, Fair Value	357	319
Derivatives Liabilities, Notional	$ 82,010	$ 82,010

Nominal or face amount used to calculate payments on the derivative asset.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5579245-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Notional Amount
-URI http://asc.fasb.org/extlink&oid=6519104

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5580258-113959

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624163-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=34720828&loc=SL20225862-175312

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=36459792&loc=SL20226000-175313

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Nominal or face amount used to calculate payments on the derivative liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Notional Amount
-URI http://asc.fasb.org/extlink&oid=6519104

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5579245-113959

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