Fair Value Measurements (Details) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Fair Value Measurements
Securities owned	$ 367,370,783	$ 358,679,830
U.S. Commercial paper
Fair Value Measurements
Transfer of securities owned from Level 1 to Level 2	15,999,008
U.S. Government-sponsored enterprises
Fair Value Measurements
Transfer of securities owned from Level 1 to Level 2	228,724,592
Recurring basis \| Level 1
Fair Value Measurements
Total	4,499,803	488,123,092
Recurring basis \| Level 1 \| U.S. and foreign futures contracts
Fair Value Measurements
Equity in brokers' trading accounts	4,390,480	2,225,736
Recurring basis \| Level 1 \| Options on futures contracts
Fair Value Measurements
Equity in brokers' trading accounts	20,797
Recurring basis \| Level 1 \| Bank deposits
Fair Value Measurements
Cash and cash equivalents	88,526
Recurring basis \| Level 1 \| U.S. Commercial paper
Fair Value Measurements
Cash and cash equivalents		183,847,222
Securities owned		25,782,069
Recurring basis \| Level 1 \| U.S. Government-sponsored enterprises
Fair Value Measurements
Securities owned		266,282,515
Recurring basis \| Level 1 \| U.S. Government securities
Fair Value Measurements
Securities owned		9,985,550
Recurring basis \| Level 2
Fair Value Measurements
Total	494,883,311	75,433,303
Recurring basis \| Level 2 \| Forward contracts
Fair Value Measurements
Equity in brokers' trading accounts	285,382	1,444,845
Recurring basis \| Level 2 \| Options on forward contracts
Fair Value Measurements
Equity in brokers' trading accounts	(152,674)	10,638
Recurring basis \| Level 2 \| Bank deposits
Fair Value Measurements
Cash and cash equivalents		17,348,124
Recurring basis \| Level 2 \| U.S. Commercial paper
Fair Value Measurements
Cash and cash equivalents	127,379,820
Securities owned	36,692,006
Recurring basis \| Level 2 \| U.S. Government-sponsored enterprises
Fair Value Measurements
Securities owned	248,728,397
Recurring basis \| Level 2 \| Corporate bonds
Fair Value Measurements
Securities owned	81,950,380	56,629,696
Recurring basis \| Total
Fair Value Measurements
Total	499,383,114	563,556,395
Recurring basis \| Total \| U.S. and foreign futures contracts
Fair Value Measurements
Equity in brokers' trading accounts	4,390,480	2,225,736
Recurring basis \| Total \| Forward contracts
Fair Value Measurements
Equity in brokers' trading accounts	285,382	1,444,845
Recurring basis \| Total \| Options on futures contracts
Fair Value Measurements
Equity in brokers' trading accounts	20,797
Recurring basis \| Total \| Options on forward contracts
Fair Value Measurements
Equity in brokers' trading accounts	(152,674)	10,638
Recurring basis \| Total \| Bank deposits
Fair Value Measurements
Cash and cash equivalents	88,526	17,348,124
Recurring basis \| Total \| U.S. Commercial paper
Fair Value Measurements
Cash and cash equivalents	127,379,820	183,847,222
Securities owned	36,692,006	25,782,069
Recurring basis \| Total \| U.S. Government-sponsored enterprises
Fair Value Measurements
Securities owned	248,728,397	266,282,515
Recurring basis \| Total \| Corporate bonds
Fair Value Measurements
Securities owned	81,950,380	56,629,696
Recurring basis \| Total \| U.S. Government securities
Fair Value Measurements
Securities owned		$ 9,985,550

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.

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The aggregate fair value as of the balance sheet date of financial instruments and other positions owned by the entity including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities. Includes both pledged and unpledged holdings.

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