Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues
Investment banking	$ 27,694	$ 18,666	$ 70,431	$ 50,550
Brokerage	28,462	22,701	86,583	71,282
Management fees	9,327	8,866	28,518	28,515
Incentive income	2,521	1,416	7,086	2,687
Interest and dividends	10,969	3,605	30,905	14,845
Reimbursement from affiliates	1,386	1,370	4,085	3,796
Other revenues	556	701	1,519	2,398
Consolidated Funds
Interest and dividends	255	24	414	115
Other revenues	190	249	267	359
Total revenues	81,360	57,598	229,808	174,547
Expenses
Employee compensation and benefits	53,614	47,322	145,344	137,102
Floor brokerage and trade execution	4,033	3,058	13,479	10,992
Interest and dividends	6,133	2,056	20,287	7,107
Professional, advisory and other fees	4,022	3,534	10,878	11,158
Service fees	2,351	2,807	7,615	8,198
Communications	4,670	4,522	13,423	11,775
Occupancy and equipment	6,752	5,808	19,019	16,594
Depreciation and amortization	2,624	2,427	7,786	6,945
Client services and business development	3,493	3,510	12,251	11,089
Other expenses	3,595	3,680	10,142	10,919
Consolidated Funds
Interest and dividends	96	2	157	22
Professional, advisory and other fees	230	263	717	1,112
Floor brokerage and trade execution	91	0	196	0
Other expenses	33	65	167	205
Total expenses	91,737	79,054	261,461	233,218
Other income (loss)
Net gains (losses) on securities, derivatives and other investments	15,469	12,510	32,873	41,969
Consolidated Funds
Net realized and unrealized gains (losses) on investments and other transactions	3,096	(2,730)	11,274	817
Net realized and unrealized gains (losses) on derivatives	(32)	212	430	626
Net gains (losses) on foreign currency transactions	168	9	1	(6)
Total other income (loss)	18,701	10,001	44,578	43,406
Income (loss) before income taxes	8,324	(11,455)	12,925	(15,265)
Income tax expense (benefit)	(46)	163	288	496
Net income (loss)	8,370	(11,618)	12,637	(15,761)
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries	4,759	(1,033)	10,509	(1,225)
Net income (loss) attributable to Cowen Group, Inc. stockholders	$ 3,611	$ (10,585)	$ 2,128	$ (14,536)
Weighted average common shares outstanding:
Basic (in shares)	118,359	114,989	116,012	114,587
Diluted (in shares)	122,708	114,989	119,891	114,587
Earnings (loss) per share:
Basic (in dollars per share)	$ 0.03	$ (0.09)	$ 0.02	$ (0.13)
Diluted (in dollars per share)	$ 0.03	$ (0.09)	$ 0.02	$ (0.13)