Goodwill and Intangibles Schedule of Goodwill by Segment (Details) (Annual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill [Roll Forward]
Goodwill, Gross	$ 54,591	$ 54,591
Goodwill, Impaired, Accumulated Impairment Loss	(19,685)	(17,351)
Goodwill	34,906	37,240
Goodwill, Acquired During Period	23,455	0
Goodwill impairment	0	(2,334)	$ 0
Goodwill, Gross	78,046	54,591	54,591
Goodwill, Impaired, Accumulated Impairment Loss	(19,685)	(19,685)	(17,351)
Goodwill	58,361	34,906	37,240
Alternative Investment
Goodwill [Roll Forward]
Goodwill, Gross	30,228	30,228
Goodwill, Impaired, Accumulated Impairment Loss	(10,200)	(10,200)
Goodwill	20,028	20,028
Goodwill, Acquired During Period	0	0
Goodwill impairment	0	0
Goodwill, Gross	30,228	30,228	30,228
Goodwill, Impaired, Accumulated Impairment Loss	(10,200)	(10,200)	(10,200)
Goodwill	20,028	20,028	20,028
Broker-Dealer
Goodwill [Roll Forward]
Goodwill, Gross	24,363	24,363
Goodwill, Impaired, Accumulated Impairment Loss	(9,485)	(7,151)
Goodwill	14,878	17,212
Goodwill, Acquired During Period	23,455	0
Goodwill impairment	0	(2,334)
Goodwill, Gross	47,818	24,363	24,363
Goodwill, Impaired, Accumulated Impairment Loss	(9,485)	(9,485)	(7,151)
Goodwill	$ 38,333	14,878	$ 17,212
Cowen Prime and Cowen Prime Trading
Goodwill [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years 3 months 22 days
Cowen Equity Finance | Broker-Dealer
Goodwill [Roll Forward]
Goodwill impairment		$ (2,300)