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
Jun. 30, 2013
Dec. 31, 2012
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned $ 6,920 $ 2,078
Securities sold, but not yet purchased (4,619) (292)
Certificates of deposit
    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned 16 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 3,242 1,098
Securities sold, but not yet purchased (2,406) (123)
U.S. Treasury notes
    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned 95 0
Securities sold, but not yet purchased 0 (99)
Common stock and warrants
    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned 3,202 384
Securities sold, but not yet purchased (2,213) (70)
Restricted common stock and warrants
    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned 365 582
Securities sold, but not yet purchased $ 0 $ 0