Customer Concentration - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2013 Customer	Jun. 30, 2012 Customer
Risks And Uncertainties [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	12.10%	13.90%