Customer Concentration (Details)	12 Months Ended
	Dec. 31, 2012 customer	Dec. 31, 2011 customer	Dec. 31, 2010 customer
Customer Concentration (Textual) [Abstract]
Number of client accounted for total revenue	0	0	0
Total revenue, accounted for single client	More than 10%	More than 10%	More than 10%
Percentage of trading volumes by single client	13.50%	14.60%	15.80%
Percentage of outstanding shares owned by single client	7.00%