Name:	bhlb_SecurityOwnedAndPledgedAsCollateralAmortizedCostAbstract
Namespace Prefix:	bhlb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Represents the cost of financial instrument held by the entity for its own account (proprietary securities) and pledged to swap counterparties as collateral for interest rate swap transactions.

No definition available.

Name:	bhlb_SecurityOwnedAndPledgedAsCollateralForInterestRateSwapAmortizedCost
Namespace Prefix:	bhlb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Fair value of financial instrument held by the entity for its own account (proprietary securities) that are carried at fair value and pledged to swap counterparties as collateral for interest rate swap transactions.

No definition available.

Name:	bhlb_SecurityOwnedAndPledgedAsCollateralForInterestRateSwapFairValue
Namespace Prefix:	bhlb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represents the cost of financial instrument held by the entity for its own account (proprietary securities) and pledged for municipal deposits.

No definition available.

Name:	bhlb_SecurityOwnedAndPledgedAsCollateralForMunicipalDepositsAmortizedCost
Namespace Prefix:	bhlb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Fair value of financial instrument held by the entity for its own account (proprietary securities) that are carried at fair value and pledged as collateral for municipal deposits.

No definition available.

Name:	bhlb_SecurityOwnedAndPledgedAsCollateralForMunicipalDepositsFairValue
Namespace Prefix:	bhlb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

Name:	us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Fair value of liabilities arising from or related to a financial instrument held by the entity for its own account (proprietary securities) which has been pledged to counterparties.

No definition available.