Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenues
Investment banking	$ 45,799	$ 27,694	$ 125,653	$ 70,431
Brokerage	34,334	28,462	100,475	86,583
Management fees	9,796	9,327	28,412	28,518
Incentive income	(837)	2,521	4,385	7,086
Interest and dividends	13,725	10,969	35,437	30,905
Reimbursement from affiliates	2,473	2,175	7,391	6,451
Other revenues	1,120	556	2,427	1,519
Consolidated Funds
Interest and dividends	642	255	1,783	414
Other revenues	49	190	717	267
Total revenues	107,101	82,149	306,680	232,174
Expenses
Employee compensation and benefits	65,806	53,614	197,771	145,344
Floor brokerage and trade execution	5,125	5,421	16,638	17,669
Interest and dividends	12,429	6,281	29,694	20,886
Professional, advisory and other fees	4,621	4,022	12,596	10,878
Service fees	1,933	2,351	6,161	7,615
Communications	3,286	3,481	9,554	9,991
Occupancy and equipment	6,650	6,752	19,371	19,019
Depreciation and amortization	2,274	2,624	7,036	7,786
Client services and business development	6,577	3,493	16,726	12,251
Other expenses	3,364	3,248	9,750	8,785
Consolidated Funds
Interest and dividends	218	96	517	157
Professional, advisory and other fees	348	230	622	717
Floor brokerage and trade execution	1	91	7	196
Other expenses	68	33	189	167
Total expenses	112,700	91,737	326,632	261,461
Other income (loss)
Net gains (losses) on securities, derivatives and other investments	13,836	14,680	48,227	30,507
Consolidated Funds
Net realized and unrealized gains (losses) on investments and other transactions	532	3,096	8,474	11,274
Gain (Loss) on Derivative Instruments, Net, Pretax	1,899	(32)	1,688	430
Net gains (losses) on foreign currency transactions	2	168	(17)	1
Total other income (loss)	16,269	17,912	58,372	42,212
Income (loss) before income taxes	10,670	8,324	38,420	12,925
Income tax expense (benefit)	141	(46)	266	288
Net income (loss)	10,529	8,370	38,154	12,637
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	4,006	4,759	13,409	10,509
Net income (loss) attributable to Cowen Group, Inc. stockholders	$ 6,523	$ 3,611	$ 24,745	$ 2,128
Weighted average common shares outstanding:
Basic (in shares)	114,969	118,359	115,407	116,012
Diluted (in shares)	118,801	122,708	120,027	119,891
Earnings (loss) per share:
Earnings Per Share, Basic	$ 0.06	$ 0.03	$ 0.21	$ 0.02
Earnings Per Share, Diluted	$ 0.05	$ 0.03	$ 0.21	$ 0.02