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Customer Concentration	3 Months Ended
Customer Concentration	Mar. 31, 2018
Risks And Uncertainties [Abstract]
Customer Concentration	11. Customer Concentration During both the three months ended March 31, 2018 and 2017, no single client accounted for more than 10% of total revenue. One institutional investor client accounted for 10.7% and 13.2% of trading volumes during the three months ended March 31, 2018 and 2017, respectively.