XML 83 R41.htm IDEA: XBRL DOCUMENT v2.4.1.9
LOANS (Details) (USD $)
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Loans      
Loans $ 4,728,663,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome   $ 4,680,600,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
Activity in the accretable yield for the acquired loan portfolio      
Balance at beginning of period 2,541,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield 2,559,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield  
Reclassification from nonaccretable difference for loans with improved cash flows 1,330,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldReclassificationsFromNonaccretableDifference 1,540,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldReclassificationsFromNonaccretableDifference  
Accretion (440,000)us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAccretion (945,000)us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAccretion  
Balance at end of period 3,431,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield 3,154,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield  
Business Activity      
Loans      
Loans 4,013,669,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
  3,918,880,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
Acquired Loans      
Loans      
Number of branches 20bhlb_BusinessAcquisitionNumberOfRetailBankBranchesAcquired
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
   
Loans 714,994,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
  761,720,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
Carrying amount of loans considered impaired at the acquisition date 12,700,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
  13,800,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
Note balance of loans considered impaired at the acquisition date 23,900,000bhlb_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesNoteBalanceNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
  25,800,000bhlb_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesNoteBalanceNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
Carrying amount of loans not considered impaired at the acquisition date 702,000,000bhlb_FinancingReceivableNotConsideredImpairedAtTimeOfAcquisition
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
  747,900,000bhlb_FinancingReceivableNotConsideredImpairedAtTimeOfAcquisition
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
Residential | Mortgages      
Loans      
Loans 1,473,239,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
  1,496,204,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Residential | Mortgages | Business Activity      
Loans      
Loans 1,215,814,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
  1,226,452,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Residential | Mortgages | Acquired Loans      
Loans      
Loans 257,425,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
  269,752,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Carrying amount of loans considered impaired at the acquisition date 361,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
  375,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Residential | Mortgages | 1-4 family      
Loans      
Loans 1,444,521,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
  1,468,142,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
Residential | Mortgages | 1-4 family | Business Activity      
Loans      
Loans 1,188,018,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
  1,199,408,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
Residential | Mortgages | 1-4 family | Acquired Loans      
Loans      
Loans 256,503,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
  268,734,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
Carrying amount of loans considered impaired at the acquisition date 361,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
  375,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
Residential | Mortgages | Construction      
Loans      
Loans 28,718,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
  28,062,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
Residential | Mortgages | Construction | Business Activity      
Loans      
Loans 27,796,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
  27,044,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
Residential | Mortgages | Construction | Acquired Loans      
Loans      
Loans 922,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
  1,018,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
Commercial real estate      
Loans      
Loans 1,672,099,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
  1,611,567,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial real estate | Business Activity      
Loans      
Loans 1,411,990,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
  1,340,076,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial real estate | Acquired Loans      
Loans      
Loans 260,109,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
  271,491,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Carrying amount of loans considered impaired at the acquisition date 11,427,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
  12,277,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial real estate | Other commercial and industrial loans      
Loans      
Loans 1,294,527,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
  1,244,959,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial real estate | Other commercial and industrial loans | Business Activity      
Loans      
Loans 1,086,893,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
  1,030,837,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial real estate | Other commercial and industrial loans | Acquired Loans      
Loans      
Loans 207,634,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
  214,122,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial real estate | Construction      
Loans      
Loans 186,846,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
  173,390,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
Commercial real estate | Construction | Business Activity      
Loans      
Loans 182,800,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
  169,189,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
Commercial real estate | Construction | Acquired Loans      
Loans      
Loans 4,046,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
  4,201,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
Carrying amount of loans considered impaired at the acquisition date 1,281,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
  1,296,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
Commercial real estate | Single and multi-family      
Loans      
Loans 190,726,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_SingleAndMultiFamilyMember
  193,218,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_SingleAndMultiFamilyMember
Commercial real estate | Single and multi-family | Business Activity      
Loans      
Loans 142,297,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_SingleAndMultiFamilyMember
  140,050,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_SingleAndMultiFamilyMember
Commercial real estate | Single and multi-family | Acquired Loans      
Loans      
Loans 48,429,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_SingleAndMultiFamilyMember
  53,168,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_SingleAndMultiFamilyMember
Carrying amount of loans considered impaired at the acquisition date 4,924,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_SingleAndMultiFamilyMember
  5,477,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_SingleAndMultiFamilyMember
Commercial real estate | Other commercial real estate | Business Activity      
Loans      
Loans 1,086,893,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
  1,030,837,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
Commercial real estate | Other commercial real estate | Acquired Loans      
Loans      
Loans 207,634,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
  214,122,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
Carrying amount of loans considered impaired at the acquisition date 5,222,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
  5,504,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
Commercial real estate | Business loans      
Loans      
Loans 826,815,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
  804,366,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial real estate | Business loans | Business Activity      
Loans      
Loans 778,671,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
  753,191,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial real estate | Business loans | Acquired Loans      
Loans      
Loans 48,144,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
  51,175,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Carrying amount of loans considered impaired at the acquisition date 705,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
  986,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial real estate | Business loans | Asset based lending      
Loans      
Loans 354,106,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_AssetBasedLendingMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
  341,246,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_AssetBasedLendingMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial real estate | Business loans | Asset based lending | Business Activity      
Loans      
Loans 354,106,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_AssetBasedLendingMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
  341,246,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_AssetBasedLendingMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial real estate | Business loans | Other commercial and industrial loans      
Loans      
Loans 472,709,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
  463,120,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial real estate | Business loans | Other commercial and industrial loans | Business Activity      
Loans      
Loans 424,565,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
  411,945,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial real estate | Business loans | Other commercial and industrial loans | Acquired Loans      
Loans      
Loans 48,144,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
  51,175,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Carrying amount of loans considered impaired at the acquisition date 705,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
  986,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Consumer      
Loans      
Loans 756,510,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  768,463,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Consumer | Business Activity      
Loans      
Loans 607,194,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  599,161,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Consumer | Acquired Loans      
Loans      
Loans 149,316,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  169,302,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Carrying amount of loans considered impaired at the acquisition date 170,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  171,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Consumer | Home equity      
Loans      
Loans 317,615,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  318,632,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Consumer | Home equity | Business Activity      
Loans      
Loans 255,368,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  252,681,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Consumer | Home equity | Acquired Loans      
Loans      
Loans 62,247,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  65,951,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Carrying amount of loans considered impaired at the acquisition date 170,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  171,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Consumer | Auto and other      
Loans      
Loans 438,895,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_AutoAndOtherReceivableMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  449,831,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_AutoAndOtherReceivableMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Consumer | Auto and other | Business Activity      
Loans      
Loans 351,826,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_AutoAndOtherReceivableMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  346,480,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_AutoAndOtherReceivableMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Consumer | Auto and other | Acquired Loans      
Loans      
Loans 87,069,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_AutoAndOtherReceivableMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  103,351,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_AutoAndOtherReceivableMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Commercial      
Loans      
Loans 2,498,914,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
  2,415,933,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Commercial | Business Activity      
Loans      
Loans 2,190,661,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
  2,093,267,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Commercial | Acquired Loans      
Loans      
Loans $ 308,253,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
  $ 322,666,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember