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