Condensed Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total		Treasury Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings/(Accumulated deficit)	Cumulative Preferred Stock	Common Stock Class A
Balance at Dec. 31, 2014	$ 677,675		$ (79,771)	$ 772,296	$ 17	$ (16,027)	$ 0	$ 1,160
Common Stock, Shares, Outstanding at Dec. 31, 2014								111,691,199.000
Preferred stock, shares outstanding at Dec. 31, 2014							0
Redeemable Noncontrolling Interest at Dec. 31, 2014	86,076
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to Cowen Group, Inc.	16,698					16,698
Net income (loss) attributable to redeemable non-controlling interests	2,720
Foreign currency translation	(2)	[1]			(2)
Capital contributions	3,379
Capital withdrawals	(6,210)
Restricted stock awards issued, shares								1,367,618
Purchase of treasury stock, at cost, shares								(1,889,920)
Purchase of treasury stock, at cost	(9,982)
Preferred stock dividends	0
Income tax effect from share based compensation	1,536
Amortization of share based compensation	4,162
Balance at Mar. 31, 2015	690,087		(89,753)	777,994	15	671	$ 0	$ 1,160
Common Stock, Shares, Outstanding at Mar. 31, 2015								111,168,897
Preferred stock, shares outstanding at Mar. 31, 2015							0
Redeemable Noncontrolling Interest at Mar. 31, 2015	85,965
Balance at Dec. 31, 2015	$ 789,993		(137,356)	902,554	0	23,627	$ 1	$ 1,167
Common Stock, Shares, Outstanding at Dec. 31, 2015								105,604,658
Preferred stock, shares outstanding at Dec. 31, 2015	120,750						120,750,000
Redeemable Noncontrolling Interest at Dec. 31, 2015	$ 186,911
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to Cowen Group, Inc.	(3,698)					(3,698)
Net income (loss) attributable to redeemable non-controlling interests	(4,297)
Foreign currency translation	(3)	[1]			(3)
Capital contributions	217,633
Capital withdrawals	(2,267)
Deconsolidation of entity	(73,042)
Restricted stock awards issued, shares								2,596,342
Purchase of treasury stock, at cost, shares								(2,122,795)
Purchase of treasury stock, at cost	(7,582)
Preferred stock dividends	(1,698)
Income tax effect from share based compensation	(515)
Amortization of share based compensation	6,423
Balance at Mar. 31, 2016	$ 782,920		$ (144,938)	$ 908,462	$ (3)	$ 18,231	$ 1	$ 1,167
Common Stock, Shares, Outstanding at Mar. 31, 2016								106,078,205
Preferred stock, shares outstanding at Mar. 31, 2016	120,750						120,750,000
Redeemable Noncontrolling Interest at Mar. 31, 2016	$ 324,938

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