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Customer Concentration	6 Months Ended
Customer Concentration	Jun. 30, 2015
Risks And Uncertainties [Abstract]
Customer Concentration	11. Customer Concentration During both the six months ended June 30, 2015 and 2014, no single client accounted for more than 10% of total revenue. One institutional investor client accounted for 14.5% and 14.9% of trading volumes during the six months ended June 30, 2015 and 2014, respectively.