OPERATING SEGMENTS (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015 segment	Mar. 31, 2014
Operating segments
Number of reportable operating segments	2us-gaap_NumberOfReportableSegments
Net interest income	$ 45,493us-gaap_InterestIncomeExpenseNet	$ 42,766us-gaap_InterestIncomeExpenseNet
Provision for loan losses	3,851us-gaap_ProvisionForLoanAndLeaseLosses	3,396us-gaap_ProvisionForLoanAndLeaseLosses
Non-interest income	12,562us-gaap_NoninterestIncome	4,423us-gaap_NoninterestIncome
Non-interest expense	45,148us-gaap_NoninterestExpense	45,360us-gaap_NoninterestExpense
Income before income taxes	9,056	(1,567)
Income tax expense (benefit)	297us-gaap_IncomeTaxExpenseBenefit	(461)us-gaap_IncomeTaxExpenseBenefit
Net income (loss)	8,759	(1,106)
Average assets (in millions)	6,497bhlb_SegmentReportingAverageAssets	5,851bhlb_SegmentReportingAverageAssets
Operating segment \| Banking
Operating segments
Net interest income	46,339	43,712
Provision for loan losses	3,851	3,396
Non-interest income	9,413	1,374
Non-interest expense	42,494	42,574
Income before income taxes	9,407	(884)
Income tax expense (benefit)	433	(192)
Net income (loss)	8,974	(692)
Average assets (in millions)	6,479	5,829
Operating segment \| Insurance
Operating segments
Non-interest income	2,967	3,049
Non-interest expense	1,939	2,322
Income before income taxes	1,028	727
Income tax expense (benefit)	399	287
Net income (loss)	629	440
Average assets (in millions)	28	26
Reportable legal entity \| Berkshire Hills Bancorp
Operating segments
Net interest income	5,154	(946)
Non-interest income	3,785	(252)
Non-interest expense	715	464
Income before income taxes	8,224	(1,662)
Income tax expense (benefit)	(535)	(556)
Net income (loss)	8,759	(1,106)
Average assets (in millions)	757	722
Eliminations
Operating segments
Net interest income	(6,000)
Non-interest income	(3,603)	252
Income before income taxes	(9,603)	252
Net income (loss)	(9,603)	252
Average assets (in millions)	$ (767)	$ (726)

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Sum of operating profit and nonoperating income or expense before Income or Loss from equity method investments, income taxes, extraordinary items, and noncontrolling interest.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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The net amount of operating interest income (expense).

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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Total aggregate amount of all noninterest expense.

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The total amount of noninterest income which may be derived from: (1) fees and commissions; (2) premiums earned; (3) insurance policy charges; (4) the sale or disposal of assets; and (5) other sources not otherwise specified.

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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Amount of expense related to estimated loss from loan and lease transactions.

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