Quarterly report pursuant to sections 13 or 15(d)

Off-Balance-Sheet Risk and Concentration of Credit Risk - Additional Information (Detail)

v2.4.0.6
Off-Balance-Sheet Risk and Concentration of Credit Risk - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Off-Balance-Sheet Risk and Concentration of Credit Risk [Abstract]    
Receivables from clearing broker $ 20,508 $ 16,973