Derivative Financial Instruments - Fair Value of Derivative Instruments (Details) $ in Thousands	Mar. 31, 2017 USD ($) contract	Dec. 31, 2016 USD ($) contract
Assets
Fair Value	$ 62,490	$ 111,977
Net amounts per Consolidated Statement of Financial Condition	12,649	19,405
Liabilities
Fair Value	91,221	109,662
Net amounts per Consolidated Statement of Financial Condition	36,433	14,560
Foreign currency, Futures contracts \| Receivable from brokers, dealers and clearing organizations
Assets
Fair Value	$ 163	$ 360
Contracts \| contract	364	1,285
Liabilities
Fair Value	$ 240	$ 1,663
Contracts \| contract	438	6,495
Foreign currency, Forward contracts \| Financial instruments owned, at fair value
Assets
Fair Value	$ 0	$ 30
Contracts \| contract	0	1
Liabilities
Fair Value	$ 598	$ 0
Contracts \| contract	1	0
Equity, Futures contracts \| Receivable from brokers, dealers and clearing organizations
Assets
Fair Value	$ 1,594	$ 1,451
Contracts \| contract	7,047	2,056
Liabilities
Fair Value	$ 2,978	$ 1,644
Contracts \| contract	7,326	2,944
Equity, Swap contracts \| Receivable from brokers, dealers and clearing organizations
Assets
Fair Value	$ 0	$ 16
Contracts \| contract	0	1
Liabilities
Fair Value	$ 195	$ 154
Contracts \| contract	2	1
Equity, Listed options \| Financial instruments owned/sold, not yet purchased, at fair value
Assets
Fair Value	$ 12,299	$ 19,100
Contracts \| contract	75,294	85,797
Liabilities
Fair Value	$ 35,835	$ 12,961
Contracts \| contract	76,347	90,063
Equity, Forward contracts \| Accrued expenses and other liabilities
Assets
Fair Value		$ 0
Contracts \| contract		0
Liabilities
Fair Value		$ 1,599
Contracts \| contract		1
Fixed income, Futures contracts \| Receivable from brokers, dealers and clearing organizations
Assets
Fair Value	$ 2,545	$ 4,627
Contracts \| contract	4,234	8,590
Liabilities
Fair Value	$ 5,678	$ 5,541
Contracts \| contract	4,038	5,165
Commodity, Futures contracts \| Receivable from brokers, dealers and clearing organizations
Assets
Fair Value	$ 45,889	$ 86,393
Contracts \| contract	23,531	31,800
Liabilities
Fair Value	$ 45,697	$ 86,100
Contracts \| contract	25,762	31,906
Futures contracts and listed options \| Exchange traded
Assets
Less: Legally enforceable master netting agreements	$ (49,841)	$ (92,572)
Liabilities
Less: Legally enforceable master netting agreements	(54,593)	(94,948)
Swaps \| Bi-lateral over-the-counter
Assets
Less: Legally enforceable master netting agreements	0	0
Liabilities
Less: Legally enforceable master netting agreements	$ (195)	$ (154)

Fair value of liability associated with 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.

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