Annual report pursuant to Section 13 and 15(d)

Securities Owned and Securities Sold, But Not Yet Purchased (Components of Securities Owned and Securities Sold, but not yet Purchased) (Details)

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Securities Owned and Securities Sold, But Not Yet Purchased (Components of Securities Owned and Securities Sold, but not yet Purchased) (Details) - USD ($)
$ in Thousands
Dec. 31, 2015
Dec. 31, 2014
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned $ 4,079 $ 5,910
Securities Sold, But Not Yet Purchased (238) (230)
Certificates of Deposit    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 359 465
Securities Sold, But Not Yet Purchased 0 0
Debt Securities    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 1,125 1,526
Securities Sold, But Not Yet Purchased (30) (45)
U.S. Treasury Notes    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 101 102
Securities Sold, But Not Yet Purchased (200) (151)
Common Stock and Warrants    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 927 1,981
Securities Sold, But Not Yet Purchased (8) (34)
Restricted Common Stock and Warrants    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 958 875
Securities Sold, But Not Yet Purchased 0 0
Other Investments    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities Owned 609 961
Securities Sold, But Not Yet Purchased $ 0 $ 0