Quarterly report pursuant to sections 13 or 15(d)

Securities Owned and Securities Sold, But Not Yet Purchased - Additional Information (Detail)

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Securities Owned and Securities Sold, But Not Yet Purchased - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities owned deposited with the Company's subsidiaries clearing broker $ 486 $ 542
Securities owned at fair value 1,132 2,014
Common stock and warrants
   
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities owned at fair value 177 191
Fair Value, Inputs, Level 2 | Common stock and warrants | Warrants to purchase common stock
   
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities owned at fair value $ 468 $ 1,005