Name:	bhlb_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarningsRelatedToAssetsStillHeld
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Represents the number of securities in the entity's security portfolio.

No definition available.

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Namespace Prefix:	bhlb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

The sum of the periodic adjustments of the differences between securities' face values and purchase prices that are charged against earnings. This is called accretion if the security was purchased at a discount and amortization if it was purchased at premium. As a noncash item, this element is an adjustment to net income when calculating cash provided by or used in operations using the indirect method.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 28

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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Amount of gain (loss) recognized in earnings, arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3).

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Amount of gain (loss) recognized in other comprehensive income, arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3).

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

Sales that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

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Transfers out of assets measured at fair value and categorized within Level 3 of the fair value hierarchy that have taken place during the period.

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Value of loans and leases held in the entity's portfolio transferred to loans and leases held-for-sale in noncash transactions.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4313-108586

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 32

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.