Goodwill and Intangibles Schedule of Intangible Assets (Details) (Annual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 53,964	$ 34,064
Intangible assets, accumulated amortization (in dollars)	(28,301)	(25,581)
Intangible Assets, Net	25,663	8,483
Amortization of Intangible Assets	$ 2,700	3,600	$ 3,700
Investment Contracts
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	5 years
Finite-Lived Intangible Assets, Gross	$ 3,900	3,900
Intangible assets, accumulated amortization (in dollars)	(3,900)	(3,900)
Intangible Assets, Net	0	0
Trade Names
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	9,712	9,612
Intangible assets, accumulated amortization (in dollars)	(8,897)	(8,305)
Intangible Assets, Net	815	1,307
Customer Relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	29,484	13,284
Intangible assets, accumulated amortization (in dollars)	(10,338)	(8,936)
Intangible Assets, Net	$ 19,146	4,348
Customer Contracts
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	1 year 2 months 12 days
Finite-Lived Intangible Assets, Gross	$ 800	800
Intangible assets, accumulated amortization (in dollars)	(800)	(800)
Intangible Assets, Net	0	0
Noncompete agreements and covenants with limiting conditions acquired
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	1,831	31
Intangible assets, accumulated amortization (in dollars)	(172)	(21)
Intangible Assets, Net	1,659	10
Intellectual property
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	8,237	6,437
Intangible assets, accumulated amortization (in dollars)	(4,194)	(3,619)
Intangible Assets, Net	4,043	2,818
Cowen Equity Finance
Acquired Finite-Lived Intangible Assets [Line Items]
Impairment of Intangible Assets, Finite-lived		$ 900
Cowen Prime and Cowen Prime Trading
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Net (Including Goodwill)	$ 19,900
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years 3 months 22 days
Minimum | Trade Names
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	1 year
Minimum | Customer Relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	3 years
Minimum | Noncompete agreements and covenants with limiting conditions acquired
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	3 years
Minimum | Intellectual property
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	3 years
Minimum | Cowen Prime and Cowen Prime Trading
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	1 year
Maximum | Trade Names
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	7 years 6 months
Maximum | Customer Relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	14 years
Maximum | Noncompete agreements and covenants with limiting conditions acquired
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	5 years
Maximum | Intellectual property
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	10 years
Maximum | Cowen Prime and Cowen Prime Trading
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	14 years