Goodwill and Intangible Assets Schedule of Goodwill by Segment (Details) (USD $)	12 Months Ended			3 Months Ended	12 Months Ended			12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2013 Dahlman Rose & Company, LLC	Dec. 31, 2013 Alternative Investment	Dec. 31, 2012 Alternative Investment	Dec. 31, 2011 Alternative Investment	Dec. 31, 2009 Alternative Investment Prior transactions [Member]	Dec. 31, 2013 Broker-Dealer	Dec. 31, 2012 Broker-Dealer	Dec. 31, 2011 Broker-Dealer	Dec. 31, 2009 Broker-Dealer Prior transactions [Member]	Dec. 31, 2013 Broker-Dealer ATM Group and Cowen Equity Finance LP [Member]
Goodwill [Line Items]
Goodwill, Gross	$ 54,591,000	$ 45,896,000	$ 37,379,000		$ 30,228,000	$ 30,228,000	$ 30,228,000		$ 24,363,000	$ 15,668,000	$ 7,151,000
Goodwill other changes				8,700,000				30,200,000				7,200,000	8,500,000
Goodwill, Acquired During Period	8,695,000	8,517,000			0	0			8,695,000	8,517,000
Goodwill impairment	0	0	(7,151,000)		0	0			0	0	(7,200,000)
Goodwill, Impaired, Accumulated Impairment Loss	(17,351,000)	(17,351,000)	(17,351,000)		(10,200,000)	(10,200,000)	(10,200,000)		(7,151,000)	(7,151,000)	(7,151,000)
Goodwill	$ 37,240,000	$ 28,545,000	$ 20,028,000		$ 20,028,000	$ 20,028,000	$ 20,028,000		$ 17,212,000	$ 8,517,000	$ 0