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
Mar. 31, 2016
Dec. 31, 2015
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned $ 3,780 $ 4,079
Securities Sold, But Not Yet Purchased (311) (238)
Certificates of deposit    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 339 359
Securities Sold, But Not Yet Purchased 0 0
Debt securities    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 1,586 1,125
Securities Sold, But Not Yet Purchased (42) (30)
U.S. Treasury notes    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 102 101
Securities Sold, But Not Yet Purchased (247) (200)
Common stock and warrants    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 373 927
Securities Sold, But Not Yet Purchased (22) (8)
Restricted common stock and warrants    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 775 958
Securities Sold, But Not Yet Purchased 0 0
Other investments    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 605 609
Securities Sold, But Not Yet Purchased $ 0 $ 0