XML 47 R71.htm IDEA: XBRL DOCUMENT v2.4.1.9
LOANS (Details 5) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Cash Basis Interest Income Recognized    
Additional funds committed amount $ 0bhlb_ImpairedFinancingReceivableAdditionalFundsCommittedAmount  
Business Activity    
Recorded Investment    
Total 25,305us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
29,279us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
Unpaid Principal Balance    
Total 26,448us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
30,561us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
Related Allowance    
With an allowance recorded 1,143us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
1,282us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
Average Recorded Investment    
Total 29,689us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
36,407us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
Cash Basis Interest Income Recognized    
Total 1,043us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
1,190us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
Acquired Loans    
Recorded Investment    
Total 6,399us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
7,627us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
Unpaid Principal Balance    
Total 6,570us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
8,384us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
Related Allowance    
With an allowance recorded 171us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
757us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
Average Recorded Investment    
Total 7,122us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
6,280us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
Cash Basis Interest Income Recognized    
Total 272us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
215us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
Other commercial real estate | Business Activity    
Recorded Investment    
With no related allowance 102us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
18,909us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
With an allowance recorded   125us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
Unpaid Principal Balance    
With no related allowance 102us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
18,909us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
With an allowance recorded   344us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
Related Allowance    
With an allowance recorded   219us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
Impaired Financing Receivable, with No Related Allowance, Recorded Investment 102us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
18,909us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
Average Recorded Investment    
With no related allowance 9us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
22,653us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
Cash Basis Interest Income Recognized    
With no related allowance   885us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
Other commercial real estate | Acquired Loans    
Recorded Investment    
With no related allowance 5,206us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
3,853us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
With an allowance recorded 383us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
1,954us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
Total   5,807us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
Unpaid Principal Balance    
With no related allowance 5,206us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
3,853us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
With an allowance recorded 431us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
2,442us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
Total   6,295us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
Related Allowance    
With an allowance recorded 48us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
488us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
Impaired Financing Receivable, with No Related Allowance, Recorded Investment 5,206us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
3,853us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
Average Recorded Investment    
With no related allowance   2,864us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
With an allowance recorded   1,997us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
Cash Basis Interest Income Recognized    
With no related allowance   111us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
With an allowance recorded   67us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
Residential | Mortgages | Business Activity    
Recorded Investment    
Total 3,083us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
5,332us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Unpaid Principal Balance    
Total 3,238us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
6,237us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Related Allowance    
With an allowance recorded 155us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
905us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Average Recorded Investment    
Total 4,455us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
6,567us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Cash Basis Interest Income Recognized    
Total 172us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
194us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Residential | Mortgages | Acquired Loans    
Recorded Investment    
Total 647us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
1,338us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Unpaid Principal Balance    
Total 695us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
1,568us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Related Allowance    
With an allowance recorded 48us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
230us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Average Recorded Investment    
Total 1,082us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
1,150us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Cash Basis Interest Income Recognized    
Total 22us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
28us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Residential | Mortgages | 1-4 family | Business Activity    
Recorded Investment    
With no related allowance 2,528us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
3,406us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
With an allowance recorded 555us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
1,926us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
Unpaid Principal Balance    
With no related allowance 2,528us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
3,406us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
With an allowance recorded 710us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
2,831us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
Related Allowance    
With an allowance recorded 155us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
905us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
Impaired Financing Receivable, with No Related Allowance, Recorded Investment 2,528us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
3,406us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
Average Recorded Investment    
With no related allowance 3,807us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
4,208us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
With an allowance recorded 648us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
2,359us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
Cash Basis Interest Income Recognized    
With no related allowance 141us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
150us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
With an allowance recorded 31us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
44us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod
/ 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    
Recorded Investment    
With no related allowance 189us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
381us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
With an allowance recorded 458us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
957us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
Unpaid Principal Balance    
With no related allowance 189us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
381us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
With an allowance recorded 506us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
1,187us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
Related Allowance    
With an allowance recorded 48us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
230us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
Impaired Financing Receivable, with No Related Allowance, Recorded Investment 189us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
381us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
Average Recorded Investment    
With no related allowance 841us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
736us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
With an allowance recorded 241us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
414us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
Cash Basis Interest Income Recognized    
With no related allowance 8us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
5us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
With an allowance recorded 14us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
23us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_Family1To4Member
Commercial real estate | Business Activity    
Recorded Investment    
Total 21,093us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
22,210us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Unpaid Principal Balance    
Total 22,015us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
22,429us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Related Allowance    
With an allowance recorded 922us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
219us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Average Recorded Investment    
Total 22,796us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
26,753us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Cash Basis Interest Income Recognized    
Total 788us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
915us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial real estate | Acquired Loans    
Recorded Investment    
Total 5,589us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
 
Unpaid Principal Balance    
Total 5,637us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
 
Related Allowance    
With an allowance recorded 48us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
 
Average Recorded Investment    
Total 5,592us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
4,861us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Cash Basis Interest Income Recognized    
Total 231us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
178us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial real estate | Construction | Business Activity    
Recorded Investment    
With no related allowance 16,990us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
3,176us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
With an allowance recorded 3,511us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
 
Unpaid Principal Balance    
With no related allowance 16,990us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
3,176us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
With an allowance recorded 4,431us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
 
Related Allowance    
With an allowance recorded 920us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
 
Impaired Financing Receivable, with No Related Allowance, Recorded Investment 16,990us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
3,176us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
Average Recorded Investment    
With no related allowance 18,218us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
3,997us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
Cash Basis Interest Income Recognized    
With no related allowance 704us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
30us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
Commercial real estate | Construction | Acquired Loans    
Average Recorded Investment    
With no related allowance 5,484us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
 
Cash Basis Interest Income Recognized    
With no related allowance 227us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
 
Commercial real estate | Single and multi-family | Business Activity    
Recorded Investment    
With an allowance recorded 490us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_SingleAndMultiFamilyMember
 
Unpaid Principal Balance    
With an allowance recorded 492us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_SingleAndMultiFamilyMember
 
Related Allowance    
With an allowance recorded 2us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_SingleAndMultiFamilyMember
 
Average Recorded Investment    
With no related allowance 519us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_SingleAndMultiFamilyMember
 
With an allowance recorded 1,213us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= bhlb_SingleAndMultiFamilyMember
 
Commercial real estate | Other commercial real estate | Acquired Loans    
Average Recorded Investment    
With an allowance recorded 108us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
 
Cash Basis Interest Income Recognized    
With an allowance recorded 4us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember
 
Commercial real estate | Business loans | Business Activity    
Recorded Investment    
Total 743us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
1,325us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Unpaid Principal Balance    
Total 743us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
1,380us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Related Allowance    
With an allowance recorded   55us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Average Recorded Investment    
With no related allowance 1,877us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
1,833us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
With an allowance recorded   14us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Total 1,877us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
1,847us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Cash Basis Interest Income Recognized    
With no related allowance 70us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
61us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
With an allowance recorded   3us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Total 70us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
64us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial real estate | Business loans | Acquired Loans    
Recorded Investment    
Total 39us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
 
Unpaid Principal Balance    
Total 39us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
 
Average Recorded Investment    
With no related allowance 356us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
231us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Total 356us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
231us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Cash Basis Interest Income Recognized    
With no related allowance 13us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
6us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Total 13us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
6us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial real estate | Business loans | Other commercial and industrial loans | Business Activity    
Recorded Investment    
With no related allowance 743us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
811us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
With an allowance recorded   514us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Unpaid Principal Balance    
With no related allowance 743us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
811us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
With an allowance recorded   569us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Related Allowance    
With an allowance recorded   55us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Impaired Financing Receivable, with No Related Allowance, Recorded Investment 743us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
811us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ 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    
Recorded Investment    
With no related allowance 39us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
367us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Total   367us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Unpaid Principal Balance    
With no related allowance 39us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
367us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Total   367us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Related Allowance    
Impaired Financing Receivable, with No Related Allowance, Recorded Investment 39us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
367us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherCommercialBusinessLoanMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Consumer | Business Activity    
Recorded Investment    
Total 386us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
412us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Unpaid Principal Balance    
Total 452us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
515us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Related Allowance    
With an allowance recorded 66us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
103us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Average Recorded Investment    
Total 561us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
1,240us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Cash Basis Interest Income Recognized    
Total 13us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
17us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Consumer | Acquired Loans    
Recorded Investment    
Total 124us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
 
Unpaid Principal Balance    
Total 199us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
 
Related Allowance    
With an allowance recorded 75us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
 
Average Recorded Investment    
Total 92us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
38us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Cash Basis Interest Income Recognized    
Total 6us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
3us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Consumer | Home equity | Business Activity    
Recorded Investment    
With no related allowance 87us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
270us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
With an allowance recorded 194us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
142us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Unpaid Principal Balance    
With no related allowance 87us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
270us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
With an allowance recorded 248us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
245us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Related Allowance    
With an allowance recorded 54us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
103us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Impaired Financing Receivable, with No Related Allowance, Recorded Investment 87us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
270us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Average Recorded Investment    
With no related allowance 234us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
1,008us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
With an allowance recorded 207us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
103us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Cash Basis Interest Income Recognized    
With no related allowance 3us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
9us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
With an allowance recorded 6us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
3us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Consumer | Home equity | Acquired Loans    
Recorded Investment    
With an allowance recorded 124us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
115us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Total   115us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Unpaid Principal Balance    
With an allowance recorded 199us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
154us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Total   154us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Related Allowance    
With an allowance recorded 75us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
39us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Average Recorded Investment    
With no related allowance 41us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
 
Consumer | Other | Business Activity    
Recorded Investment    
With an allowance recorded 105us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherReceivableMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
 
Unpaid Principal Balance    
With an allowance recorded 117us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherReceivableMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
 
Related Allowance    
With an allowance recorded 12us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherReceivableMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
 
Average Recorded Investment    
With no related allowance   129us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherReceivableMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
With an allowance recorded 120us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherReceivableMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
 
Cash Basis Interest Income Recognized    
With no related allowance   5us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherReceivableMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
With an allowance recorded 4us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= bhlb_OtherReceivableMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
 
Commercial | Home equity | Acquired Loans    
Average Recorded Investment    
With an allowance recorded 51us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
38us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Cash Basis Interest Income Recognized    
With an allowance recorded 6us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
3us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_HomeEquityMember
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansAcquiredFromBusinessCombinationsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Commercial | Mortgages | Construction | Business Activity    
Average Recorded Investment    
With an allowance recorded 2,837us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
 
Cash Basis Interest Income Recognized    
With an allowance recorded 84us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ConstructionLoansMember
 
Commercial | Mortgages | Other commercial real estate | Business Activity    
Average Recorded Investment    
With an allowance recorded   $ 103us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ bhlb_AccountsNotesLoansAndFinancingReceivableBySourceAxis
= bhlb_LoansFromBusinessActivitiesMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_MortgagesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstateMember