Annual report pursuant to Section 13 and 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
Dec. 31, 2018
Jan. 01, 2018
Dec. 31, 2017
Debt and Equity Securities, FV-NI [Line Items]      
Securities owned deposited with the Company's subsidiaries clearing broker $ 9,763   $ 3,265
Securities owned, at fair value 10,923 $ 3,881 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 $ 1,052   $ 475