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
Jun. 30, 2016
Dec. 31, 2015
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value $ 3,763 $ 4,079
Securities sold, but not yet purchased, at fair value (628) (238)
Level 1    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 817 1,286
Securities sold, but not yet purchased, at fair value (350) (8)
Level 2    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 2,946 2,793
Securities sold, but not yet purchased, at fair value (278) (230)
Level 3    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 0 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 326 359
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 326 359
Certificates of deposit | Level 2    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 0 0
Certificates of deposit | Level 3    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 0 0
Debt securities    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 1,412 1,125
Securities sold, but not yet purchased, at fair value (278) (30)
Debt securities | Level 1    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 0 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 1,412 1,125
Securities sold, but not yet purchased, at fair value (278) (30)
Debt securities | Level 3    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 0 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 0 (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 0
Securities sold, but not yet purchased, at fair value   0
U.S. Treasury notes | Level 2    
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   (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 0
Securities sold, but not yet purchased, at fair value   0
Common stock and warrants    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 1,322 1,885
Securities sold, but not yet purchased, at fair value (350) (8)
Common stock and warrants | Level 1    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 491 927
Securities sold, but not yet purchased, at fair value (350) (8)
Common stock and warrants | Level 2    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 831 958
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 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 601 609
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 0
Other investments | Level 2    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value 601 609
Other investments | Level 3    
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]    
Securities owned, at fair value $ 0 $ 0