Derivative Financial Instruments - Fair Value of Derivative Instruments (Details) $ in Thousands	Dec. 31, 2016 USD ($) contract	Dec. 31, 2015 USD ($) contract
Assets
Fair Value	$ 111,977	$ 220,647
Net amounts per Consolidated Statement of Financial Condition	19,405	179,501
Liabilities
Fair Value	109,662	194,723
Net amounts per Consolidated Statement of Financial Condition	14,560	151,893
Foreign currency, Futures contracts \| Receivable from brokers, dealers and clearing organizations
Assets
Fair Value	$ 360	$ 578
Contracts \| contract	1,285	3,675
Liabilities
Fair Value	$ 1,663	$ 955
Contracts \| contract	6,495	6,586
Foreign currency, Forward contracts \| Financial instruments owned, at fair value
Assets
Fair Value	$ 30	$ 445
Contracts \| contract	1	1
Liabilities
Fair Value	$ 0	$ 0
Contracts \| contract	0	0
Equity, Futures contracts \| Receivable from brokers, dealers and clearing organizations
Assets
Fair Value	$ 1,451	$ 1,558
Contracts \| contract	2,056	4,038
Liabilities
Fair Value	$ 1,644	$ 1,743
Contracts \| contract	2,944	3,432
Equity, Swap contracts \| Receivable from brokers, dealers and clearing organizations
Assets
Fair Value	$ 16	$ 0
Contracts \| contract	1	0
Liabilities
Fair Value	$ 154	$ 281
Contracts \| contract	1	2
Equity, Listed options \| Financial instruments owned/sold, not yet purchased, at fair value
Assets
Fair Value	$ 19,100	$ 178,360
Contracts \| contract	85,797	360,469
Liabilities
Fair Value	$ 12,961	$ 151,893
Contracts \| contract	90,063	390,949
Equity, Forward contracts \| Financial instruments owned/sold, not yet purchased, at fair value
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	$ 4,627	$ 4,265
Contracts \| contract	8,590	6,195
Liabilities
Fair Value	$ 5,541	$ 4,037
Contracts \| contract	5,165	4,891
Commodity, Futures contracts \| Receivable from brokers, dealers and clearing organizations
Assets
Fair Value	$ 86,393	$ 35,441
Contracts \| contract	31,800	22,424
Liabilities
Fair Value	$ 86,100	$ 35,814
Contracts \| contract	31,906	24,261
Futures contracts and listed options \| Exchange traded
Assets
Less: Legally enforceable master netting agreements	$ (92,572)	$ (41,146)
Liabilities
Less: Legally enforceable master netting agreements	(94,948)	(42,549)
Swaps \| Bi-lateral over-the-counter
Assets
Less: Legally enforceable master netting agreements	0	0
Liabilities
Less: Legally enforceable master netting agreements	$ (154)	$ (281)

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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