Derivative Instruments - Fair Value of Derivative Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Equities futures \| Receivables from broker dealers and clearing organizations
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	$ 427	$ 2,403
Derivatives Assets, Notional	654,155	1,461,286
Equities futures \| Payables to broker dealers and clearing organizations
Fair value of derivative instruments on a gross basis
Derivatives Liabilities, Fair Value	(1,632)	(43)
Derivatives Liabilities, Notional	220,751	62,417
Commodity futures \| Receivables from broker dealers and clearing organizations
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	(23,638)	13,964
Derivatives Assets, Notional	5,612,720	3,918,778
Commodity futures \| Payables to broker dealers and clearing organizations
Fair value of derivative instruments on a gross basis
Derivatives Liabilities, Fair Value	(3,091)	2,842
Derivatives Liabilities, Notional	20,879,583	22,616,170
Currency futures \| Receivables from broker dealers and clearing organizations
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	12,902	1,591
Derivatives Assets, Notional	3,219,766	3,264,093
Currency futures \| Payables to broker dealers and clearing organizations
Fair value of derivative instruments on a gross basis
Derivatives Liabilities, Fair Value	(19)	(6,282)
Derivatives Liabilities, Notional	1,713,567	1,137,908
Fixed Income futures \| Receivables from broker dealers and clearing organizations
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	(71)	31
Derivatives Assets, Notional	3,609	5,730
Options
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	266	141
Derivatives Liabilities, Fair Value	228	80
Options \| Receivables from broker dealers and clearing organizations
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	266	141
Derivatives Assets, Notional	9,876	6,844
Currency forwards
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	1,756,179	1,147,261
Derivatives Liabilities, Fair Value	1,792,466	1,009,038
Currency forwards \| Financial instruments owned
Fair value of derivative instruments on a gross basis
Derivatives Assets, Fair Value	1,756,179	1,147,261
Derivatives Assets, Notional	165,982,871	94,192,414
Currency forwards \| Financial instruments sold, not yet purchased
Fair value of derivative instruments on a gross basis
Derivatives Liabilities, Fair Value	228	80
Derivatives Liabilities, Notional	15,124	4,486
Interest rate swaps \| Financial instruments sold, not yet purchased
Fair value of derivative instruments on a gross basis
Derivatives Liabilities, Fair Value	1,792,466	1,009,038
Derivatives Liabilities, Notional	$ 169,531,047	$ 85,874,684

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=64837297&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
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+ References

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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