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)	Call Option	Cumulative Preferred Stock	Common Stock Class A
Balance at Dec. 31, 2012		$ 495,109		$ (31,728)	$ 713,211	$ 356	$ (187,865)		$ 0	$ 1,135
Common Stock, Shares, Outstanding at Dec. 31, 2012										112,447,892
Preferred stock, shares outstanding at Dec. 31, 2012									0
Redeemable Noncontrolling Interest at Dec. 31, 2012		85,703
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to Cowen Group, Inc.		4,647					4,647
Net income (loss) attributable to redeemable non-controlling interests		13,193
Defined benefit plans		246	[1]			246
Foreign currency translation		(10)	[1]			(10)
Capital contributions		15,181
Capital withdrawals		(28,263)
Restricted stock awards issued, shares										4,668,423
Purchase of treasury stock, at cost, shares										(4,606,073)
Purchase of treasury stock, at cost		(16,446)
Treasury stock reissued, cost		90
Treasury Stock Reissued at Lower than Repurchase Price							(25)
Preferred stock dividends		0
Common stock issuance upon acquisition, shares										2,491,647
Common stock issuance upon acquisition		6,240			6,215					$ 25
Amortization of share based compensation		17,915
Balance at Dec. 31, 2013		507,766		(48,084)	737,341	592	(183,243)		$ 0	$ 1,160
Common Stock, Shares, Outstanding at Dec. 31, 2013										115,026,633
Preferred stock, shares outstanding at Dec. 31, 2013									0
Redeemable Noncontrolling Interest at Dec. 31, 2013		85,814
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to Cowen Group, Inc.		167,216					167,216
Net income (loss) attributable to redeemable non-controlling interests		15,564
Defined benefit plans		(344)	[1]			(344)
Foreign currency translation		(231)	[1]			(231)
Capital contributions		10,441
Capital withdrawals		(24,585)
Deconsolidation of entity		(1,158)
Restricted stock awards issued, shares										4,265,339
Purchase of treasury stock, at cost, shares										(7,634,107)
Purchase of treasury stock, at cost		(31,687)
Preferred stock dividends		0
Common stock issuance upon acquisition		0
Warrants issued		15,218
Income tax effect from share based compensation		1,324
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period										33,334
Stock Options Exercised, Common Stock										$ 0
Stock options exercised, APIC		116			116
Amortization of share based compensation		18,297
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
Preferred stock, shares outstanding at Dec. 31, 2014		0							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.		43,729					43,729
Net income (loss) attributable to redeemable non-controlling interests		15,246
Defined benefit plans	[1]	0
Foreign currency translation		(17)	[1]			(17)
Capital contributions		110,178
Capital withdrawals		(24,589)
Restricted stock awards issued, shares										4,272,910
Purchase of treasury stock, at cost, shares										(11,008,078)
Purchase of treasury stock, at cost		(57,585)
Preferred stock issuance, net of issuance costs									120,750
Preferred stock issuance, net of issuance costs		117,195			117,194				$ 1
Preferred stock dividends		(4,075)
Common stock issuance upon acquisition, shares										548,625
Common stock issuance upon acquisition		3,008			3,002					$ 6
Capped call option transaction								$ (15,878)
Income tax effect from share based compensation		3,806
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period										100,002
Stock Options Exercised, Common Stock										$ 1
Stock options exercised, APIC		395			394
Amortization of share based compensation		21,740
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
Redeemable Noncontrolling Interest at Dec. 31, 2015		$ 186,911

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