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Cash and Securities Segregated for Regulatory and Other Purposes - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2013
Dec. 31, 2012
Brokers And Dealers [Abstract]    
Deposits held in special reserve bank accounts $ 35.5 $ 32.0
Client funds held in escrow $ 251.4 $ 242.7