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Represents the amount of common stock of a trust held by the entity.

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Represents the period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, bearing fixed interest rate.

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Represents the discount rate at the issuance of the debt instrument.

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Represents the period up to which the interest payments may be deferred.

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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No definition available.

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Face (par) amount of debt instrument at time of issuance.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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No definition available.

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Amount of Federal Home Loan Bank (FHLB) advances which have floating interest rates.

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Amount of advances from Federal Home Loan Bank (FHLBank) maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Including the current and noncurrent portions, the carrying value of junior subordinated long-term debt owed to unconsolidated subsidiary trusts as of the balance sheet date. Such debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets and was initially scheduled to be repaid after one year or beyond the normal operating cycle if longer.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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BORROWED FUNDS - Narrative (Details) - USD ($)	1 Months Ended	12 Months Ended
BORROWED FUNDS - Narrative (Details) - USD ($)	Sep. 30, 2012	Dec. 31, 2019	Dec. 31, 2018
Borrowings and junior subordinated debentures
Short-term borrowings		$ 125,000,000	$ 1,118,832,000
Long-term borrowings		702,550,000	398,984,000
Variable-rate FHLB advances		0	0
Advances from the FHLBB
Borrowings and junior subordinated debentures
FHLBB advances		0
Line of credit		3,000,000.0
Outstanding balance, line of credit		0	0
Short-term borrowings		125,000,000	1,118,832,000
Long-term borrowings		605,501,000	309,466,000
Federal Reserve Bank Advances
Borrowings and junior subordinated debentures
Short-term borrowings		0	0
Federal Home Loan Bank Certificates And Obligations F H L B Callable Advances
Borrowings and junior subordinated debentures
Long-term borrowings		10,000,000
Federal Home Loan Bank Certificates And Obligations F H L B Amortizing Advances
Borrowings and junior subordinated debentures
Long-term borrowings		4,400,000	1,700,000
Subordinated notes
Borrowings and junior subordinated debentures
Long-term borrowings		74,232,000	74,054,000
Maturity period	15 years
Principal amount of debt issued	$ 75,000,000.0
Discount rate (percent)	1.15%
Fixed interest rate (percent)	6.875%
Maturity period with fixed interest rate	10 years
Subordinated notes \| Three-month LIBOR rate
Borrowings and junior subordinated debentures
Interest rate margin (percent)	5.113%
Unamortized debt issuance costs		338,000	461,000
Junior subordinated borrowing - Trust I
Borrowings and junior subordinated debentures
Long-term borrowings		$ 15,464,000	$ 15,464,000
Junior subordinated borrowing - Trust I \| Berkshire Hills Capital Trust I
Borrowings and junior subordinated debentures
Common stock of trust (percent)		100.00%
Common stock of trust included in other asset		$ 500,000
Sole asset of trust in form of debt		$ 15,500,000
Variable interest rate (percent)		3.76%	4.50%
Period up to which interest payments can be deferred		5 years
Junior subordinated borrowing - Trust I \| SI Capital Trust II
Borrowings and junior subordinated debentures
Common stock of trust (percent)		100.00%
Common stock of trust included in other asset		$ 200,000
Sole asset of trust in form of debt		$ 8,200,000
Variable interest rate (percent)		3.59%
Period up to which interest payments can be deferred		5 years
Junior subordinated borrowing - Trust I \| LIBOR \| Berkshire Hills Capital Trust I
Borrowings and junior subordinated debentures
Interest rate margin (percent)		1.85%
Junior subordinated borrowing - Trust I \| LIBOR \| SI Capital Trust II
Borrowings and junior subordinated debentures
Interest rate margin (percent)		1.70%