Condensed Consolidated Statements of Changes in Equity (USD $)	Total USD ($)		Common Stock USD ($)	Treasury Stock USD ($)	Additional Paid-in Capital USD ($)	Accumulated Other Comprehensive Income (Loss) USD ($)	Retained Earnings/(Accumulated deficit) USD ($)	Redeemable Non-controlling Interest USD ($)	LaBranche and Co Inc. [Member] Common Stock
Balance at Dec. 31, 2010	$ 449,256,000		$ 726,000	$ 0	$ 504,480,000	$ 20,000	$ (55,970,000)	$ 144,346,000
Balance, shares at Dec. 31, 2010			75,490,209
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to Cowen Group, Inc. stockholders	(108,010,000)						(108,010,000)
Net income (loss) attributable to redeemable non-controlling interests	5,827,000							5,827,000
Defined benefit plans	25,000	[1]				25,000
Foreign currency translation	(260,000)	[1]				(260,000)
Capital contributions								4,038,000
Capital withdrawals								(53,094,000)
Consolidation of funds								3,470,000
Restricted stock awards issued, shares			3,053,298
Common stock issued upon acquisition (See Note 2)	156,048,000		409,000		155,639,000
Common stock issued upon acquisition (See Note 2), shares									40,850,133
Treasury stock re-issuance	0
Purchase of treasury stock, at cost	(16,902,000)			(16,902,000)
Purchase of treasury stock, at cost, shares				(5,346,003)
Amortization of share based compensation	28,308,000				28,308,000
Balance at Dec. 31, 2011	508,465,000		1,135,000	(16,902,000)	688,427,000	(215,000)	(163,980,000)	104,587,000
Balance, shares at Dec. 31, 2011			114,047,637
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to Cowen Group, Inc. stockholders	(23,885,000)						(23,885,000)
Net income (loss) attributable to redeemable non-controlling interests	(72,000)							(72,000)
Defined benefit plans	423,000	[1]				423,000
Foreign currency translation	148,000	[1]				148,000
Capital contributions								500,000
Capital withdrawals								(20,729,000)
Deconsolidation of funds								(17,104,000)
Consolidation of funds								18,521,000
Restricted stock awards issued, shares			4,346,472
Common stock issued upon acquisition (See Note 2)	0
Purchase of treasury stock, at cost	(14,826,000)			(14,826,000)
Purchase of treasury stock, at cost, shares				(5,946,217)
Amortization of share based compensation	24,784,000				24,784,000
Balance at Dec. 31, 2012	495,109,000		1,135,000	(31,728,000)	713,211,000	356,000	(187,865,000)	85,703,000
Balance, shares at Dec. 31, 2012			112,447,892
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to Cowen Group, Inc. stockholders	4,647,000						4,647,000
Net income (loss) attributable to redeemable non-controlling interests	13,193,000							13,193,000
Defined benefit plans	246,000	[1]				246,000
Foreign currency translation	(10,000)	[1]				(10,000)
Capital contributions								15,181,000
Capital withdrawals								(28,263,000)
Restricted stock awards issued, shares			4,668,423
Common stock issued upon acquisition (See Note 2)	6,240,000		25,000		6,215,000
Common stock issued upon acquisition (See Note 2), shares			2,491,647
Treasury stock re-issuance	90,000			90,000
Treasury Stock Reissued at Lower than Repurchase Price				(25,000)
Treasury stock reissued during the period net of gain(loss)	65,000
Treasury stock re-issuance, shares				24,744
Purchase of treasury stock, at cost	(16,446,000)			(16,446,000)
Purchase of treasury stock, at cost, shares				(4,606,073)
Amortization of share based compensation	17,915,000				17,915,000
Balance at Dec. 31, 2013	$ 507,766,000		$ 1,160,000	$ (48,084,000)	$ 737,341,000	$ 592,000	$ (183,243,000)	$ 85,814,000
Balance, shares at Dec. 31, 2013			115,026,633

[1] (a) During the periods presented, the Company did not have material reclassifications out of other comprehensive income.