Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Revenues
Investment banking	$ 14,343	$ 9,938	$ 29,025	$ 15,943
Brokerage	24,607	29,793	52,198	59,369
Management fees	11,857	8,881	23,021	18,151
Incentive income	675	(100)	5,056	1,994
Interest and dividends	5,840	1,380	10,399	2,183
Reimbursement from affiliates	981	1,741	1,990	3,484
Other revenues	232	398	922	1,020
Total revenues	58,679	55,000	122,924	111,260
Expenses
Employee compensation and benefits	43,575	38,547	88,662	81,980
Floor brokerage and trade execution	3,685	3,945	7,795	8,973
Interest and dividends	3,115	621	5,724	1,067
Professional, advisory and other fees	10,398	2,879	17,538	5,267
Service fees	4,366	4,034	7,978	7,853
Communications	4,342	3,153	7,235	6,454
Occupancy and equipment	4,991	5,845	10,113	11,474
Depreciation and amortization	2,011	2,390	4,069	4,884
Client services and business development	4,132	4,379	8,809	8,544
Other	(259)	4,710	4,034	12,092
Total expenses	81,228	71,685	163,458	152,928
Other income (loss)
Net gains (losses) on securities, derivatives and other investments	76	249	17,358	1,774
Bargain purchase gain	22,244		22,244
Total other income	27,090	(6,465)	46,118	13,332
Income (loss) before income taxes	4,541	(23,150)	5,584	(28,336)
Income tax expense (benefit)	(17,954)	599	(17,791)	333
Net income (loss)	22,495	(23,749)	23,375	(28,669)
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries	2,458	(2,552)	3,256	5,504
Net income (loss) attributable to Cowen Group, Inc. stockholders	20,037	(21,197)	20,119	(34,173)
Weighted average common shares outstanding:
Basic (in shares)	76,330	72,693	75,600	72,601
Diluted (in shares)	77,898	72,693	76,889	72,601
Earnings (loss) per share:
Basic (in dollars per share)	$ 0.26	$ (0.29)	$ 0.27	$ (0.47)
Diluted (in dollars per share)	$ 0.26	$ (0.29)	$ 0.26	$ (0.47)
Consolidated Funds
Revenues
Interest and dividends	136	2,965	305	8,746
Other revenues	8	4	8	370
Expenses
Floor brokerage and trade execution		285		994
Interest and dividends	40	(177)	87	1,390
Professional, advisory and other fees	613	831	1,073	1,509
Other	219	243	341	447
Other income (loss)
Net realized and unrealized gains (losses) on investments and other transactions	4,971	(8,211)	7,314	11,006
Net realized and unrealized gains (losses) on derivatives	(84)	720	(525)	500
Net gains (losses) on foreign currency transactions	$ (117)	$ 777	$ (273)	$ 52