Quarterly report pursuant to sections 13 or 15(d)

Securities Owned and Securities Sold, But Not Yet Purchased - Narrative (Details)

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Securities Owned and Securities Sold, But Not Yet Purchased - Narrative (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities owned deposited with the Company's subsidiaries clearing broker $ 2,645 $ 1,787
Securities owned at fair value 3,066 2,078
Common stock and warrants
   
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities owned at fair value 737 384
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 $ 239 $ 160