Goodwill and Intangibles Schedule of Intangible Assets (Details) (USD $)	12 Months Ended							12 Months Ended				12 Months Ended						12 Months Ended				12 Months Ended			12 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Investment Contracts	Dec. 31, 2011 Investment Contracts	Dec. 31, 2012 Trade Names	Dec. 31, 2011 Trade Names	Dec. 31, 2012 Trade Names Minimum	Dec. 31, 2012 Trade Names Maximum	Dec. 31, 2012 Customer Relationships	Dec. 31, 2011 Customer Relationships	Dec. 31, 2012 Customer Relationships Minimum	Dec. 31, 2012 Customer Relationships Maximum	Dec. 31, 2012 Customer Contracts	Dec. 31, 2011 Customer Contracts	Dec. 31, 2012 Noncompete agreements and covenants with limiting conditions acquired	Dec. 31, 2011 Noncompete agreements and covenants with limiting conditions acquired	Dec. 31, 2012 Noncompete agreements and covenants with limiting conditions acquired Minimum	Dec. 31, 2012 Noncompete agreements and covenants with limiting conditions acquired Maximum	Dec. 31, 2012 Intellectual property	Dec. 31, 2011 Intellectual property	Dec. 31, 2012 Intellectual property Minimum	Dec. 31, 2012 Intellectual property Maximum	Dec. 31, 2012 ATM Group and Cowen Equity Finance LP [Member]	Dec. 31, 2011 LaBranche and Co Inc. [Member]	Jun. 28, 2011 LaBranche and Co Inc. [Member]	Dec. 31, 2011 Prior transactions [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible Assets Amortization, Period for Recognition	7 years 9 months 7 days
Finite-Lived Intangible Asset, Useful Life				5 years				5 years	7 years 6 months			4 years	10 years	1 year 2 months 12 days				1 year	10 years			3 years	10 years
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangibles																										$ 5,100,000
Impairment of Intangible Assets, Finite-lived																									2,900,000		5,200,000
Amortization of Intangible Assets	2,700,000	8,100,000	3,600,000																						1,000,000
Intangibles																								9,900,000		2,770,000
Finite-Lived Intangible Assets, Gross	35,929,000	25,980,000		3,900,000	3,900,000	9,572,000	9,400,000			11,974,000	6,800,000			800,000	800,000	2,732,000	2,530,000			6,951,000	2,550,000
Intangible assets, accumulated amortization (in dollars)	(22,945,000)	(20,220,000)		(3,900,000)	(3,900,000)	(7,190,000)	(6,649,000)			(6,284,000)	(4,916,000)			(800,000)	(800,000)	(2,576,000)	(2,530,000)			(2,195,000)	(1,425,000)
Intangible Assets, Net	$ 12,984,000	$ 5,760,000		$ 0	$ 0	$ 2,382,000	$ 2,751,000			$ 5,690,000	$ 1,884,000			$ 0	$ 0	$ 156,000	$ 0			$ 4,756,000	$ 1,125,000