Annual report pursuant to Section 13 and 15(d)

Securities Owned and Securities Sold, But Not Yet Purchased (Fair Value Amount) (Details)

Securities Owned and Securities Sold, But Not Yet Purchased (Fair Value Amount) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	$ 5,910	$ 4,789
Securities sold, but not yet purchased, at fair value	(230)	(83)
Level 1 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	2,446	713
Securities sold, but not yet purchased, at fair value	(34)	(33)
Level 2 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	3,464	4,076
Securities sold, but not yet purchased, at fair value	(196)	(50)
Level 3 [Member]
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 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	465	24
Securities sold, but not yet purchased, at fair value	0	0
Certificates of Deposit [Member] \| Level 1 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	465	24
Certificates of Deposit [Member] \| Level 2 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	0	0
Certificates of Deposit [Member] \| Level 3 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	0	0
Debt Securities [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	1,526	1,402
Securities sold, but not yet purchased, at fair value	(45)	(46)
Debt Securities [Member] \| Level 1 [Member]
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 [Member] \| Level 2 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	1,526	1,402
Securities sold, but not yet purchased, at fair value	(45)	(46)
Debt Securities [Member] \| Level 3 [Member]
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 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	102	1
Securities sold, but not yet purchased, at fair value	(151)	0
U.S. Treasury Notes [Member] \| Level 1 [Member]
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 [Member] \| Level 2 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	102	1
Securities sold, but not yet purchased, at fair value	(151)
U.S. Treasury Notes [Member] \| Level 3 [Member]
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 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	2,856	1,414
Securities sold, but not yet purchased, at fair value	(34)	(37)
Common Stock and Warrants [Member] \| Level 1 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	1,981	689
Securities sold, but not yet purchased, at fair value	(34)	(33)
Common Stock and Warrants [Member] \| Level 2 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	875	725
Securities sold, but not yet purchased, at fair value	0	(4)
Common Stock and Warrants [Member] \| Level 3 [Member]
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 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	961	1,948
Securities sold, but not yet purchased, at fair value	0	0
Other Investments [Member] \| Level 1 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	0	0
Other Investments [Member] \| Level 2 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	961	1,948
Other Investments [Member] \| Level 3 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities owned, at fair value	$ 0	$ 0