Quarterly report pursuant to Section 13 or 15(d)

Fair Value of Assets and Liabilities (Narrative) (Details)

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Fair Value of Assets and Liabilities (Narrative) (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Debt and Equity Securities, FV-NI [Line Items]    
Securities owned deposited with the Company's subsidiaries clearing broker $ 5,722 $ 3,265
Securities owned, at fair value 6,548 3,881
Common Stock and Warrants | Warrants to purchase common stock | Level 2    
Debt and Equity Securities, FV-NI [Line Items]    
Securities owned, at fair value $ 708 $ 475