Quarterly report pursuant to sections 13 or 15(d)

Securities Owned and Securities Sold, But Not Yet Purchased - at Fair Value (Details)

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Securities Owned and Securities Sold, But Not Yet Purchased - at Fair Value (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned $ 3,066 $ 2,078
Securities sold, but not yet purchased (306) (292)
Certificates of deposit
    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned 6 14
Securities sold, but not yet purchased 0 0
Debt securities
    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned 1,474 1,098
Securities sold, but not yet purchased (31) (123)
U.S. Treasury notes
    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned 10 0
Securities sold, but not yet purchased (101) (99)
Common stock and warrants
    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned 737 384
Securities sold, but not yet purchased (174) (70)
Restricted common stock and warrants
    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned 839 582
Securities sold, but not yet purchased $ 0 $ 0