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Customer Concentration	9 Months Ended
Customer Concentration	Sep. 30, 2016
Risks And Uncertainties [Abstract]
Customer Concentration	11. Customer Concentration During both the nine months ended September 30, 2016 and 2015, no single client accounted for more than 10% of total revenue. One institutional investor client accounted for 14.6% and 15.5% of trading volumes during the nine months ended September 30, 2016 and 2015, respectively.