Quarterly report pursuant to Section 13 or 15(d)

Securities Owned and Securities Sold, But Not Yet Purchased - Classifications (Details)

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Securities Owned and Securities Sold, But Not Yet Purchased - Classifications (Details) - USD ($)
$ in Thousands
Mar. 31, 2016
Dec. 31, 2015
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value $ 3,780 $ 4,079
Securities sold, but not yet purchased, at fair value (311) (238)
Level 1    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   1,286
Securities sold, but not yet purchased, at fair value (22) (8)
Level 2    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   2,793
Securities sold, but not yet purchased, at fair value (289) (230)
Level 3    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   0
Securities sold, but not yet purchased, at fair value 0 0
Certificates of deposit    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 339 359
Securities sold, but not yet purchased, at fair value 0 0
Certificates of deposit | Level 1    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   359
Certificates of deposit | Level 2    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   0
Certificates of deposit | Level 3    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   0
Debt securities    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 1,586 1,125
Securities sold, but not yet purchased, at fair value (42) (30)
Debt securities | Level 1    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   0
Securities sold, but not yet purchased, at fair value 0 0
Debt securities | Level 2    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   1,125
Securities sold, but not yet purchased, at fair value (42) (30)
Debt securities | Level 3    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   0
Securities sold, but not yet purchased, at fair value 0 0
U.S. Treasury notes    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 102 101
Securities sold, but not yet purchased, at fair value (247) (200)
U.S. Treasury notes | Level 1    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   0
Securities sold, but not yet purchased, at fair value 0 0
U.S. Treasury notes | Level 2    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   101
Securities sold, but not yet purchased, at fair value (247) (200)
U.S. Treasury notes | Level 3    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   0
Securities sold, but not yet purchased, at fair value 0 0
Common stock and warrants    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   1,885
Securities sold, but not yet purchased, at fair value (22) (8)
Common stock and warrants | Level 1    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   927
Securities sold, but not yet purchased, at fair value (22) (8)
Common stock and warrants | Level 2    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   958
Securities sold, but not yet purchased, at fair value 0 0
Common stock and warrants | Level 3    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   0
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, at fair value 605 609
Securities sold, but not yet purchased, at fair value 0 0
Other investments | Level 1    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   0
Other investments | Level 2    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   609
Other investments | Level 3    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value   $ 0
Fair value    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 3,780  
Fair value | Level 1    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 712  
Fair value | Level 2    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 3,068  
Fair value | Level 3    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 0  
Fair value | Certificates of deposit    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 339  
Fair value | Certificates of deposit | Level 1    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 339  
Fair value | Certificates of deposit | Level 2    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 0  
Fair value | Certificates of deposit | Level 3    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 0  
Fair value | Debt securities    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 1,586  
Fair value | Debt securities | Level 1    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 0  
Fair value | Debt securities | Level 2    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 1,586  
Fair value | Debt securities | Level 3    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 0  
Fair value | U.S. Treasury notes    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 102  
Fair value | U.S. Treasury notes | Level 1    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 0  
Fair value | U.S. Treasury notes | Level 2    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 102  
Fair value | U.S. Treasury notes | Level 3    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 0  
Fair value | Common stock and warrants    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 1,148  
Fair value | Common stock and warrants | Level 1    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 373  
Fair value | Common stock and warrants | Level 2    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 775  
Fair value | Common stock and warrants | Level 3    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 0  
Fair value | Other investments    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 605  
Fair value | Other investments | Level 1    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 0  
Fair value | Other investments | Level 2    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 605  
Fair value | Other investments | Level 3    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value $ 0