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Customer Concentration (Details)	3 Months Ended
Customer Concentration (Details)	Mar. 31, 2013 customer	Mar. 31, 2012 customer
Customer Concentration (Textual) [Abstract]
Number of client accounted for total revenue	0	0
Total revenue, accounted for single client	More than 10%	More than 10%
Percentage of trading volumes by single client	12.70%	14.30%

Description of risks that arise due to the volume of business transacted with a particular customer. At a minimum, the description informs financial statement users of the general nature of the risk, but excludes "Information about Major Customers" that may be disclosed elsewhere (for instance, segment disclosures).

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