Condensed Consolidated Statements of Changes in Equity (USD $) In Thousands, except Share data	Total	Common Stock [Member]	Treasury Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings/(Accumulated Deficit)	Redeemable Non-controlling Interest
Balance at Dec. 31, 2011	$ 508,465	$ 1,135	$ (16,902)	$ 688,427	$ (215)	$ (163,980)	$ 104,587
Balance, shares at Dec. 31, 2011		114,047,637
Net income (loss) attributable to Cowen Group, Inc. stockholders	(3,951)					(3,951)
Net income (loss) attributable to redeemable non-controlling interests	(193)						(193)
Defined benefit plans	170				170
Foreign currency translation	72				72
Deconsolidation of funds							(17,104)
Consolidation of funds							18,521
Capital withdrawals to non-controlling interests in Consolidated Funds							(7,351)
Restricted stock awards issued, shares		2,701,314
Amortization of share based compensation	13,526			13,526
Purchase of treasury stock, at cost	(6,357)		(6,357)
Purchase of treasury stock, at cost, Shares		(2,540,683)
Balance at Jun. 30, 2012	$ 511,925	$ 1,135	$ (23,259)	$ 701,953	$ 27	$ (167,931)	$ 98,460
Balance, shares at Jun. 30, 2012		114,208,268