Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Revenues
Investment banking	$ 30,292	$ 25,571	$ 79,854	$ 42,737
Brokerage	33,311	31,521	66,141	58,121
Management fees	9,692	9,698	18,616	19,191
Incentive income	2,724	1,954	5,222	4,565
Interest and dividends	12,460	10,521	21,712	19,842
Reimbursement from affiliates	3,018	1,214	4,918	2,699
Other revenues	752	485	1,307	963
Consolidated Funds
Interest and dividends	655	241	1,141	253
Other revenues	(2)	2	668	77
Total revenues	92,902	81,207	199,579	148,448
Expenses
Employee compensation and benefits	64,404	47,507	131,965	91,730
Floor brokerage and trade execution	5,858	6,320	11,513	12,173
Interest and dividends	10,193	7,489	17,265	14,109
Professional, advisory and other fees	4,374	3,002	7,975	6,855
Service fees	2,086	2,687	4,228	5,264
Communications	3,022	2,771	6,268	6,510
Occupancy and equipment	6,324	6,548	12,721	12,267
Depreciation and amortization	2,382	2,609	4,762	5,162
Client services and business development	5,635	4,659	10,149	8,758
Other expenses	3,228	2,535	6,386	5,977
Consolidated Funds
Interest and dividends	189	106	299	106
Professional, advisory and other fees	140	92	274	488
Floor brokerage and trade execution	4	180	6	180
Other expenses	65	107	121	145
Total expenses	107,904	86,612	213,932	169,724
Other income (loss)
Net gains (losses) on securities, derivatives and other investments	23,037	4,994	34,391	16,801
Consolidated Funds
Net realized and unrealized gains (losses) on investments and other transactions	5,778	3,711	7,942	8,781
Gain (Loss) on Derivative Instruments, Net, Pretax	(190)	158	(211)	462
Net gains (losses) on foreign currency transactions	21	48	(19)	(167)
Total other income (loss)	28,646	8,911	42,103	25,877
Income (loss) before income taxes	13,644	3,506	27,750	4,601
Income tax expense (benefit)	46	158	125	334
Net income (loss)	13,598	3,348	27,625	4,267
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	5,216	2,255	9,403	5,750
Net income (loss) attributable to Cowen Group, Inc. stockholders	$ 8,382	$ 1,093	$ 18,222	$ (1,483)
Weighted average common shares outstanding:
Basic (in shares)	115,569	117,235	115,626	115,471
Diluted (in shares)	120,199	120,901	120,635	115,471
Earnings (loss) per share:
Earnings Per Share, Basic	$ 0.07	$ 0.01	$ 0.16	$ (0.01)
Earnings Per Share, Diluted	$ 0.07	$ 0.01	$ 0.15	$ (0.01)