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Customer Concentration	6 Months Ended
Customer Concentration	Jun. 30, 2017
Risks And Uncertainties [Abstract]
Customer Concentration	11. Customer Concentration During both the six months ended June 30, 2017 and 2016, no single client accounted for more than 10% of total revenue. One institutional investor client accounted for 13.2% and 15.3% of trading volumes during the six months ended June 30, 2017 and 2016, respectively.