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Significant Clients	9 Months Ended
Significant Clients	Sep. 30, 2013
Risks and Uncertainties [Abstract]
Significant Clients	Significant Clients The Company considers significant clients to be those clients who account for 10% or more of the total U.S. equity dollar value traded by the Company. No clients accounted for more than 10% of the Company’s U.S. equity dollar value traded for the three and nine months ended September 30, 2013 or 2012.