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Customer Concentration	6 Months Ended
Customer Concentration	Jun. 30, 2011
Customer Concentration [Abstract]
Customer Concentration	12. Customer Concentration During both the six months ended June 30, 2011 and 2010, no single client accounted for more than 10% of total revenue. One client accounted for 15.7% and 15.5% of trading volumes during the six months ended June 30, 2011 and 2010, respectively.