Annual report pursuant to section 13 and 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
Dec. 31, 2012
Dec. 31, 2011
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities owned deposited with the Company's subsidiaries clearing broker $ 1,787 $ 542
Securities owned, at fair value 2,078 2,014
Common Stock and Warrants [Member]
   
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities owned, at fair value 384 191
Fair Value, Inputs, Level 2
   
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities owned, at fair value 1,680 1,823
Fair Value, Inputs, Level 2 | Common Stock and Warrants [Member]
   
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities owned, at fair value 582 1,823
Fair Value, Inputs, Level 2 | Common Stock and Warrants [Member] | Warrants to purchase common stock
   
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities owned, at fair value $ 160 $ 1,005