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
Jun. 30, 2016
Dec. 31, 2015
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned $ 3,763 $ 4,079
Securities Sold, But Not Yet Purchased (628) (238)
Certificates of deposit    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 326 359
Securities Sold, But Not Yet Purchased 0 0
Debt securities    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 1,412 1,125
Securities Sold, But Not Yet Purchased (278) (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 0 (200)
Common stock and warrants    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 491 927
Securities Sold, But Not Yet Purchased (350) (8)
Restricted common stock and warrants    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 831 958
Securities Sold, But Not Yet Purchased 0 0
Other investments    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 601 609
Securities Sold, But Not Yet Purchased $ 0 $ 0