Quarterly report pursuant to Section 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
Sep. 30, 2015
Dec. 31, 2014
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned $ 4,125 $ 5,910
Securities sold, but not yet purchased, at fair value (419) (230)
Certificates of deposit    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned 423 465
Securities sold, but not yet purchased, at fair value 0 0
Debt securities    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned 1,351 1,526
Securities sold, but not yet purchased, at fair value (15) (45)
U.S. Treasury notes    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned 113 102
Securities sold, but not yet purchased, at fair value (348) (151)
Common stock and warrants    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned 716 1,981
Securities sold, but not yet purchased, at fair value (56) (34)
Restricted common stock and warrants    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned 842 875
Securities sold, but not yet purchased, at fair value 0 0
Other investments    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned 680 961
Securities sold, but not yet purchased, at fair value $ 0 $ 0