Document and Entity Information Document	3 Months Ended
	Mar. 31, 2012	May 07, 2012
Entity Registrant Name	Cowen Group, Inc.
Entity Central Index Key	0001466538
Current Fiscal Year End Date	--12-31
Current Fiscal Year End Date	Mar. 31, 2012
Entity Filer Category	Accelerated Filer
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q1
Document Type	10-Q
Amendment Flag	false
Entity Common Stock, Shares Outstanding		114,058,558