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Document and Entity Information - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2016
Feb. 24, 2017
Jun. 30, 2016
Document and Entity Information      
Entity Registrant Name BERKSHIRE HILLS BANCORP INC    
Entity Central Index Key 0001108134    
Document Type 10-K    
Document Period End Date Dec. 31, 2016    
Amendment Flag false    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Filer Category Large Accelerated Filer    
Entity Public Float     $ 819
Entity Common Stock, Shares Outstanding (shares)   35,730,100  
Document Fiscal Year Focus 2016    
Document Fiscal Period Focus FY