v2.4.0.8
Document and Entity Information (USD $)
12 Months Ended
Dec. 31, 2014
Feb. 25, 2015
Jun. 30, 2014
Document and Entity Information [Abstract]      
Entity Registrant Name Cowen Group, Inc.    
Entity Central Index Key 0001466538    
Current Fiscal Year End Date --12-31    
Entity Filer Category Accelerated Filer    
Document Type 10-K    
Document Period End Date Dec. 31, 2014    
Document Fiscal Year Focus 2014    
Document Fiscal Period Focus FY    
Amendment Flag false    
Entity Common Stock, Shares Outstanding   111,735,837  
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 448,508,183