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, 2016
Dec. 31, 2015
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned $ 3,646 $ 4,079
Securities Sold, But Not Yet Purchased (676) (238)
Certificates of deposit    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 457 359
Securities Sold, But Not Yet Purchased 0 0
Debt securities    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 1,624 1,125
Securities Sold, But Not Yet Purchased (15) (30)
U.S. Treasury notes    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 101 101
Securities Sold, But Not Yet Purchased (149) (200)
Common stock and warrants    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 255 927
Securities Sold, But Not Yet Purchased (512) (8)
Restricted common stock and warrants    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 572 958
Securities Sold, But Not Yet Purchased 0 0
Other investments    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 637 609
Securities Sold, But Not Yet Purchased $ 0 $ 0