v2.4.0.6
Document and Entity Information Document (USD $)
12 Months Ended
Dec. 31, 2011
Mar. 08, 2012
Jun. 30, 2011
Entity Registrant Name Cowen Group, Inc.    
Entity Central Index Key 0001466538    
Current Fiscal Year End Date --12-31    
Current Fiscal Year End Date Dec. 31, 2011    
Entity Filer Category Accelerated Filer    
Document Fiscal Year Focus 2011    
Document Fiscal Period Focus FY    
Document Type 10-K    
Amendment Flag false    
Entity Common Stock, Shares Outstanding   114,377,005  
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 301,319,256