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Customer Concentration	3 Months Ended
Customer Concentration	Mar. 31, 2017
Risks And Uncertainties [Abstract]
Customer Concentration	11. Customer Concentration During both the three months ended March 31, 2017 and 2016, no single client accounted for more than 10% of total revenue. One institutional investor client accounted for 13.2% and 16.4% of trading volumes during the three months ended March 31, 2017 and 2016, respectively.