Discontinued Operations and Disposal Groups [Abstract] Summary of Discontinued Operations Disposal Groups, Including Discontinued Operations [Table Text Block] Condensed Financial Information Disclosure [Abstract] CONDENSED FINANCIAL STATEMENTS OF PARENT COMPANY Condensed Financial Information of Parent Company Only Disclosure [Text Block] Fair Value Disclosures [Abstract] Fair Value Measurement Inputs and Valuation Techniques [Table] Fair Value Measurement Inputs and Valuation Techniques [Table] Measurement Frequency [Axis] Measurement Frequency [Axis] Measurement Frequency [Domain] Measurement Frequency [Domain] Non-recurring Fair Value, Nonrecurring [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Level 3 Fair Value, Inputs, Level 3 [Member] Fair Value Measurement Inputs and Valuation Techniques [Line Items] Fair Value Measurement Inputs and Valuation Techniques [Line Items] Impaired loans Impaired Loans, Fair Value Disclosure Represents the amount of impaired loans assets reported on the balance sheet at period end measured at fair value by the entity. Capitalized servicing rights Servicing Asset at Fair Value, Amount Total Assets Assets, Fair Value Disclosure Receivables [Abstract] Schedule of Loans Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Schedule of Total Unamortized Net Costs and Premiums Included in the Total Loans for Historical Loans Schedule of Unamortized Net Costs and Premiums on Accounts Notes Loans and Financing Receivable [Table Text Block] Tabular disclosure of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Schedule of Activity in the Accretable Yield for the Acquired Loan Portfolio that Falls Under the Purview of ASC 310-30, Accounting for Certain Loans or Debt Securities Acquired in a Transfer Schedule of Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Accretable Yield Movement [Table Text Block] Tabular disclosure of changes in accretable yield for purchased credit impaired finance receivables by way of additions, accretion, reclassifications and disposals during the period. Summary of Past Due Loans Financing Receivable, Past Due [Table Text Block] Summary of Information Pertaining to Non-accrual Loans Financing Receivable, Nonaccrual [Table Text Block] Schedule of Loans Evaluated for Impairment Schedule of Loans Evaluated for Impairment [Table Text Block] Tabular disclosure related to loans evaluated for impairment. Summary of Impaired Loans Impaired Financing Receivables [Table Text Block] Summary of the Average Recorded Investment and Interest Income Recognized on Impaired Loans Impaired Financing Receivables Average Balances and Related Interest Income Recognized [Table Text Block] Tabular disclosure of average recorded investment in impaired loans and related interest income recognized for the periods indicated. Schedule of Recorded Investment and Number of Modifications for TDRs Identified During the Period Financing Receivable, Troubled Debt Restructuring [Table Text Block] Schedule of TDR Activity Financing Receivable Troubled Debt Restructuring Activity [Table Text Block] Tabular disclosure of activity of troubled debt restructuring financial receivables. Retirement Benefits [Abstract] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Pension Plans Pension Plan [Member] Level 1 Fair Value, Inputs, Level 1 [Member] Level 2 Fair Value, Inputs, Level 2 [Member] Defined Benefit Plan, Plan Assets, Category [Axis] Defined Benefit Plan, Plan Assets, Category [Axis] Defined Benefit Plan, Plan Assets, Category [Domain] Defined Benefit Plan, Plan Assets, Category [Domain] Equity Mutual Funds, Large-Cap Defined Benefit Plan, Equity Mutual Funds, Large Cap [Member] Defined Benefit Plan, Equity Mutual Funds, Large Cap [Member] Equity Mutual Funds, Mid-Cap Defined Benefit Plan, Equity Securities, Mid Cap [Member] Equity Mutual Funds, Small-Cap Defined Benefit Plan, Equity Securities, Small Cap [Member] Equity Mutual Funds, International Defined Benefit Plan, Equity Securities, Non-US [Member] Fixed Income - US Core Fixed Income Funds [Member] Intermediate Duration Intermediate Duration [Member] Intermediate Duration [Member] Cash Equivalents - money market Money Market Funds [Member] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Defined benefit plan, fair value of plan assets Defined Benefit Plan, Plan Assets, Amount Share-based Payment Arrangement [Abstract] STOCK-BASED COMPENSATION PLANS Share-based Payment Arrangement [Text Block] Goodwill and Intangible Assets Disclosure [Abstract] GOODWILL AND OTHER INTANGIBLES Goodwill and Intangible Assets Disclosure [Text Block] Investments, Debt and Equity Securities [Abstract] Summary of Securities Available for Sale (AFS) and Securities Marketable Securities [Table Text Block] Schedule of Amortized Cost and Estimated Fair Value of Available for Sale (AFS) and Held to Maturity (HTM) Securities, Segregated by Contractual Maturity Investments Classified by Contractual Maturity Date [Table Text Block] Schedule of Amortized Cost and Fair Values of Pledged Securities Schedule of Financial Instruments Owned and Pledged as Collateral [Table Text Block] Schedule of Components of Net Realized Gains and Losses on the Sale of AFS Securities Schedule of Realized Gain (Loss) [Table Text Block] Schedule of Securities with Unrealized Losses, Segregated by the Duration of their Continuous Unrealized Loss Positions Schedule of Unrealized Loss on Investments [Table Text Block] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Receivable Type [Axis] Receivable Type [Axis] Receivable [Domain] Receivable [Domain] Business Activities Loans Loans From Business Activities [Member] Represents information pertaining to the loans from business activities. Acquired Loans Loans Acquired From Business Combinations [Member] Represents information pertaining to the loans acquired from business combinations. Financing Receivable Portfolio Segment [Axis] Financing Receivable Portfolio Segment [Axis] Financing Receivable Portfolio Segment [Domain] Financing Receivable Portfolio Segment [Domain] Commercial real estate Commercial Real Estate Portfolio Segment [Member] Commercial and industrial Commercial and Industrial Loans Portfolio Segment [Member] Commercial and Industrial Loans Portfolio Segment [Member] Residential Residential Portfolio Segment [Member] Consumer Consumer Portfolio Segment [Member] Class of Financing Receivable [Axis] Class of Financing Receivable [Axis] Class of Financing Receivable [Domain] Class of Financing Receivable [Domain] Construction Construction Loans [Member] Commercial real estate Other Receivable [Member] Class of financing receivables related to other financing receivables. 1-4 family 1 to 4 Family [Member] Class of financing receivables related to 1 to 4 Family financing receivables. Home equity Home Equity Loan [Member] Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Average recorded investment, with no related allowance Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment Cash basis interest income recognized, with no related allowance Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method Average recorded investment with related allowance Impaired Financing Receivable, with Related Allowance, Average Recorded Investment Cash basis interest income recognized, with related allowance Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method Average Recorded Investment Impaired Financing Receivable, Average Recorded Investment Cash Basis Interest Income Recognized Impaired Financing Receivable, Interest Income, Cash Basis Method EMPLOYEE BENEFIT PLANS Pension and Other Postretirement Benefits Disclosure [Text Block] Condensed Income Statement [Table] Condensed Income Statement [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Reportable legal entity Reportable Legal Entities [Member] Consolidated Entities [Axis] Consolidated Entities [Axis] Consolidated Entities [Domain] Consolidated Entities [Domain] Berkshire Hills Bancorp Parent Company [Member] Condensed statements of income Condensed Income Statements, Captions [Line Items] Income: Interest and Dividend Income, Operating [Abstract] Dividends from subsidiaries Investment Income, Dividend Other Other Income Total net revenue Revenues Interest expense Interest Expense Non-interest expenses Operating Expenses Total expense Interest and Operating Expense Represents the amount of interest expense and operating expenses recognized during the period. Income before income taxes and equity in undistributed income of subsidiaries Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest, Equity in Undistributed Income (Loss) of Subsidiaries Sum of operating profit and nonoperating income or expense before Income or Loss from equity method investments, income taxes, extraordinary items, noncontrolling interest, and equity in undistributed income (loss) of subsidiaries. Income tax benefit Income Tax Expense (Benefit) Income before equity in undistributed income of subsidiaries Income (Loss) from Continuing Operations after Income Taxes and before Minority Interest Income (Loss) from Equity Method Investments Sum of operating profit and nonoperating income or expense after income taxes but before Income or Loss from equity method investments, extraordinary items, and noncontrolling interest. Equity in undistributed results of operations of subsidiaries Income (Loss) from Equity Method Investments, Net of Dividends or Distributions Net income Net Income (Loss) Attributable to Parent Preferred stock dividend Preferred Stock Dividends, Income Statement Impact Income available to common shareholders Net Income (Loss) Available to Common Stockholders, Basic Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Cash and Cash Equivalents [Abstract] CASH AND CASH EQUIVALENTS Cash and Cash Equivalents Disclosure [Text Block] Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Disposal Group Name [Axis] Disposal Group Name [Axis] Disposal Group Name [Domain] Disposal Group Name [Domain] First Choice Loan Services, Inc. First Choice Loan Services, Inc. [Member] First Choice Loan Services, Inc. [Member] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Discontinued Operations, Held-for-sale Discontinued Operations, Held-for-sale [Member] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Timing of disposal, term Disposal Group, Including Discontinued Operation, Timing Of Disposal, Term Disposal Group, Including Discontinued Operation, Timing Of Disposal, Term Other Assets [Abstract] Servicing Asset at Amortized Cost [Table] Servicing Asset at Amortized Cost [Table] Operating Activities [Axis] Operating Activities [Axis] Operating Activities [Domain] Operating Activities [Domain] Continuing Operations Continuing Operations [Member] Discontinued Operations Discontinued Operations [Member] Statistical Measurement [Axis] Statistical Measurement [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Servicing Asset at Amortized Cost [Line Items] Servicing Asset at Amortized Cost [Line Items] Mortgage loans sold and serviced for others Proceeds from Sale of Mortgage Loans Held-for-sale Servicing fees Contractually Specified Servicing Fees, Amount Weighted average discount rate Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Discount Rate Pre-payment speed Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Prepayment Speed Servicing asset at amortized cost, additions Servicing Asset at Amortized Cost, Additions Servicing asset at amortized cost, change in fair value Servicing Asset at Amortized Cost, Other Changes that Affect Balance, Amount Servicing asset at amortized cost, allowance adjustment Servicing Asset at Amortized Cost, Increase (Decrease) for Valuation Allowance Adjustment Postretirement Benefits Other Postretirement Benefits Plan [Member] 2020 Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months 2021 Defined Benefit Plan, Expected Future Benefit Payment, Year Two 2022 Defined Benefit Plan, Expected Future Benefit Payment, Year Three 2023 Defined Benefit Plan, Expected Future Benefit Payment, Year Four 2024 - 2029 Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter Mortgage servicing rights activity Servicing Asset at Amortized Cost, Balance [Roll Forward] Balance at beginning of year Servicing Asset at Amortized Cost Additions Amortization Servicing Asset at Amortized Cost, Amortization Change in fair value Allowance adjustment Balance at end of year Servicing asset at fair value Financing Receivable, Credit Quality Indicator [Table] Financing Receivable, Credit Quality Indicator [Table] Financial Instrument [Axis] Financial Instrument [Axis] Financial Instruments [Domain] Financial Instruments [Domain] Mortgages Mortgages [Member] Internal Credit Assessment [Axis] Internal Credit Assessment [Axis] Internal Credit Assessment [Domain] Internal Credit Assessment [Domain] Pass Pass [Member] Special mention Special Mention [Member] Substandard Substandard [Member] Financial Instrument Performance Status [Axis] Financial Instrument Performance Status [Axis] Financial Instrument Performance Status [Domain] Financial Instrument Performance Status [Domain] Performing Performing Financial Instruments [Member] Nonperforming Nonperforming Financial Instruments [Member] Financing Receivable, Credit Quality Indicator [Line Items] Financing Receivable, Credit Quality Indicator [Line Items] Number of grades in internal loan rating system (grade) Internal Loan Rating System Number of Grades The number of grades in the reporting entity's internal loan rating system. Period within which loans are current, based on which risk rating is assigned Financing Receivable Risk Rating Current Period Represents the current period of loans based on which risk rating is assigned to loans. Delinquency period of loans based on which risk rating is assigned Financing Receivable Risk Rating Delinquency Period Represents the delinquency period of loans based on which risk rating is assigned to loans. Banking and Thrift, Interest [Abstract] Schedule of Net Interest Income After Provision for Loan Losses Interest Income and Interest Expense Disclosure [Table Text Block] Income Tax Disclosure [Abstract] Income Tax Contingency [Table] Income Tax Contingency [Table] Income Tax Authority [Axis] Income Tax Authority [Axis] Income Tax Authority [Domain] Income Tax Authority [Domain] Federal Domestic Tax Authority [Member] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] Connecticut CONNECTICUT Income Tax Contingency [Line Items] Income Tax Contingency [Line Items] Deferred tax expense Deferred Income Tax Expense (Benefit) Decrease in net deferred tax assets Deferred Tax Assets (Liabilities), Net Increase (Decrease) Deferred Tax Assets (Liabilities), Net Increase (Decrease) Decrease in deferred tax assets related to purchase accounting adjustments Deferred Income Tax Expense (Benefit), Purchase Accounting Adjustments Deferred Income Tax Expense (Benefit), Purchase Accounting Adjustments Decrease in deferred tax assets related to deferred tax expense Deferred Tax Liabilities, Deferred Expense Change in valuation allowance Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount Operating loss carryforwards Operating Loss Carryforwards Deferred tax assets, net operating losses, federal Deferred Tax Assets, Operating Loss Carryforwards, Domestic State tax basis difference, net of Federal tax benefit State Tax Basis Difference Net of Federal Tax Benefit Represents the amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized related to state tax basis difference, net of federal tax benefit. Valuation allowances Deferred Tax Assets, Valuation Allowance Schedule of Goodwill [Table] Schedule of Goodwill [Table] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] SI Financial Group, Inc. SI Financial Group, Inc. [Member] SI Financial Group, Inc. [Member] Goodwill Goodwill [Line Items] Goodwill Goodwill [Roll Forward] Balance, beginning of the period Goodwill Goodwill acquired Goodwill, Acquired During Period Adjustments Goodwill, Written off Related to Sale of Business Unit Balance, end of the period Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Carrying Amount Reported Value Measurement [Member] Fair Value Estimate of Fair Value Measurement [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Financial Assets Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract] Cash and cash equivalents Cash and Cash Equivalents, Fair Value Disclosure Trading security Debt Securities, Trading, and Equity Securities, FV-NI Marketable equity securities Equity Securities, FV-NI Securities available for sale Debt Securities, Available-for-sale Securities held to maturity Debt Securities, Held-to-maturity, Fair Value FHLB stock and restricted equity securities Federal Home Loan Bank Stock and Other Restricted Securities at Cost This element represent as Federal Home Loan Bank Stock And Other Restricted Securities. Net loans Loans Receivable, Fair Value Disclosure Loans held for sale Loans Held-for-sale, Fair Value Disclosure Accrued interest receivable Interest Receivable Derivative assets Derivative Asset, Fair Value, Gross Asset Financial Liabilities Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] Total deposits Deposits, Fair Value Disclosure Short-term debt Short-term Debt, Fair Value Long-term FHLB advances Federal Home Loan Bank Borrowings, Fair Value Disclosure Subordinated notes Subordinated Debt Obligations, Fair Value Disclosure Derivative liabilities Derivative Liability, Fair Value, Gross Liability Leases [Abstract] Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Assets, Lessee [Abstract] Assets, Lessee [Abstract] Assets, Lessee [Abstract] Operating lease right-of-use assets Operating Lease, Right-of-Use Asset Finance lease right-of-use assets Finance Lease, Right-of-Use Asset Total Lease Right-of-Use Assets Lease, Right-of-Use Asset Lease, Right-of-Use Asset Liabilities, Lessee [Abstract] Liabilities, Lessee [Abstract] Liabilities, Lessee [Abstract] Operating lease right-of-use liabilities Operating Lease, Liability Finance lease liabilities Finance Lease, Liability Total Lease Liabilities Lease, Liability Lease, Liability Financing Receivable, Allowance for Credit Loss [Table] Financing Receivable, Allowance for Credit Loss [Table] Residential mortgages Allowance for loan losses Financing Receivable, Allowance for Credit Loss [Line Items] Activity in the allowance for loan losses Allowance for Loan and Lease Losses [Roll Forward] Balance at beginning of year Loans and Leases Receivable, Allowance Charged-off loans Allowance for Loan and Lease Losses, Write-offs Recoveries on charged-off loans Allowance for Loan and Lease Loss, Recovery of Bad Debts Provision for loan losses Provision for Loan and Lease Losses Balance at end of year Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract] Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract] Individually evaluated for impairment Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment Collectively evaluated Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment Total OTHER ASSETS Other Assets Disclosure [Text Block] Commitments and Contingencies Disclosure [Abstract] OTHER COMMITMENTS, CONTINGENCIES, AND OFF-BALANCE SHEET ACTIVITIES Commitments and Contingencies Disclosure [Text Block] Quarterly Financial Information Disclosure [Abstract] QUARTERLY DATA (UNAUDITED) Quarterly Financial Information [Text Block] Cover page. Document Type Document Type Document Annual Report Document Annual Report Document Period End Date Document Period End Date Document Transition Report Document Transition Report Entity File Number Entity File Number Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Entity Tax Identification Number Entity Tax Identification Number Entity Address, Address Line One Entity Address, Address Line One Entity Address, City or Town Entity Address, City or Town Entity Address, State or Province Entity Address, State or Province Entity Address, Postal Zip Code Entity Address, Postal Zip Code City Area Code City Area Code Local Phone Number Local Phone Number Title of 12(b) Security Title of 12(b) Security Trading Symbol Trading Symbol Security Exchange Name Security Exchange Name Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Voluntary Filers Entity Current Reporting Status Entity Current Reporting Status Entity Interactive Data Current Entity Interactive Data Current Entity Filer Category Entity Filer Category Entity Small Business Entity Small Business Entity Emerging Growth Company Entity Emerging Growth Company Entity Shell Company Entity Shell Company Entity Public Float Entity Public Float Entity Common Stock, Shares Outstanding (in shares) Entity Common Stock, Shares Outstanding Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Amendment Flag Amendment Flag Current Fiscal Year End Date Current Fiscal Year End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Documents Incorporated by Reference Documents Incorporated by Reference [Text Block] INCOME TAXES Income Tax Disclosure [Text Block] Stockholders' Equity Note [Abstract] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Employee Stock Option Share-based Payment Arrangement, Option [Member] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive securities excluded from computation of earnings per share, amount (shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Schedule of Earnings Per Share Basic and Diluted [Table] Schedule of Earnings Per Share Basic and Diluted [Table] Disclosure pertaining to the entity's basic and diluted earnings per share. Award Type [Axis] Award Type [Axis] Award Type [Domain] Award Type [Domain] Unvested stock awards Restricted Stock [Member] Earnings Per Share Basic and Diluted [Line Items] Earnings Per Share Basic and Diluted [Line Items] 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. Net income from continuing operations Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent (Loss)/income from discontinued operations, net of tax Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Net income Average number of common shares issued (shares) Weighted Average Number of Shares Issued, Basic Less: average number of treasury shares (shares) Weighted Average Number of Shares, Treasury Stock Less: average number of unvested stock award shares (shares) Weighted Average Number of Shares, Restricted Stock Plus: average participating preferred shares (shares) Weighted Average Number of Shares Outstanding, Preferred Stock Weighted Average Number of Shares Outstanding, Preferred Stock Average number of basic common shares outstanding (shares) Weighted Average Number of Shares Outstanding, Basic Incremental common shares attributable to dilutive effect of share-based payment arrangements (shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Average number of diluted common shares outstanding (shares) Weighted Average Number of Shares Outstanding, Diluted Basic earnings/(loss) per share: Earnings Per Share, Basic [Abstract] Continuing operations (USD per share) Income (Loss) from Continuing Operations, Per Basic Share Discontinued operations (USD per share) Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share Basic earnings per common share (USD per share) Earnings Per Share, Basic Diluted earnings/(loss) per share: Earnings Per Share, Diluted [Abstract] Continuing Operations (USD per share) Income (Loss) from Continuing Operations, Per Diluted Share Discontinued operations (USD per share) Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share Diluted earnings per common share (USD per share) Earnings Per Share, Diluted Lessee, Operating Lease, Liability, Payment, Due [Abstract] 2020 Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months 2021 Lessee, Operating Lease, Liability, Payments, Due Year Two 2022 Lessee, Operating Lease, Liability, Payments, Due Year Three 2023 Lessee, Operating Lease, Liability, Payments, Due Year Four 2024 Lessee, Operating Lease, Liability, Payments, Due Year Five Thereafter Lessee, Operating Lease, Liability, Payments, Due after Year Five Total undiscounted lease payments Lessee, Operating Lease, Liability, Payments, Due Less amounts representing interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Lease liability Finance Lease, Liability, Payment, Due [Abstract] Finance Lease, Liability, Payment, Due [Abstract] 2020 Finance Lease, Liability, Payments, Due Next Twelve Months 2021 Finance Lease, Liability, Payments, Due Year Two 2022 Finance Lease, Liability, Payments, Due Year Three 2023 Finance Lease, Liability, Payments, Due Year Four 2024 Finance Lease, Liability, Payments, Due Year Five Thereafter Finance Lease, Liability, Payments, Due after Year Five Total undiscounted lease payments Finance Lease, Liability, Payment, Due Less amounts representing interest Finance Lease, Liability, Undiscounted Excess Amount Lease liability Schedule of Condensed Balance Sheets Condensed Balance Sheet [Table Text Block] Schedule of Condensed Statements of Income Condensed Income Statement [Table Text Block] Schedule of Condensed Statements of Cash Flows Condensed Cash Flow Statement [Table Text Block] Other Liabilities Disclosure [Abstract] Summary of Other Liabilities Other Liabilities [Table Text Block] FAIR VALUE MEASUREMENTS Fair Value Disclosures [Text Block] Business Combinations [Abstract] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] SI Financial Group, Inc. Business Acquisition [Line Items] Business Acquisition [Line Items] Gross contractual receivable amounts at acquisition Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net Contractual cash flows not expected to be collected (nonaccretable discount) Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Reclassifications to Nonaccretable Difference Expected cash flows at acquisition Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, Cash Flows Expected to be Collected at Acquisition Interest component of expected cash flows (accretable discount) Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Accretion Fair value of acquired loans Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value Schedule of Quarterly Results of Operations Quarterly Financial Information [Table Text Block] Lease Obligations Litigation accrual Loss Contingency Accrual Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Updates 2016-01 and 2018-02 Accounting Standards Updates 2016-01 And 2018-02 [Member] Accounting Standards Updates 2016-01 And 2018-02 [Member] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] AOCI Attributable to Parent AOCI Attributable to Parent [Member] Net unrealized holding gain/(loss) on AFS securities AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member] Net (loss) on effective cash flow hedging derivatives Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] Net (loss) on effective cash flow hedging derivatives Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] Net unrealized holding (loss) on pension plans Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Beginning balance Stockholders' Equity Attributable to Parent Other comprehensive gain/(loss) before reclassifications OCI, before Reclassifications, Net of Tax, Attributable to Parent Amounts reclassified from accumulated other comprehensive income Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent Total other comprehensive income/(loss) Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Less: amounts reclassified from accumulated other comprehensive income (loss) related to adoption of ASU 2016-01 and ASU 2018-02 Reclassification From AOCI, Accounting Standards Update, Current Period, Net Of Tax, Attributable To Parent Reclassification From AOCI, Accounting Standards Update, Current Period, Net Of Tax, Attributable To Parent Ending balance Recurring Fair Value, Recurring [Member] Summary of Assets and Financial Liabilities Measured at Fair Value on a Recurring Basis Segregated by the Level of the Valuation Inputs within the Fair Value Hierarchy Utilized to Measure Fair Value Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Schedule of Loans Held for Sale Fair Value Option, Disclosures [Table Text Block] Schedule of Changes in Level 3 Assets and Liabilities that were Measured at Fair Value on a Recurring Basis Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Table Text Block] Tabular disclosure of the fair value measurement of assets and liabilities using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes during the period attributable to the following: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets) and gains or losses recognized in other comprehensive income (loss), and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs), by class of asset and liabilities. Schedule of Quantitative Information about the Significant Unobservable Inputs within Level 3 Fair Value Measurement Inputs and Valuation Techniques [Table Text Block] Summary of Applicable Non-recurring Fair Value Measurements Fair Value Measurements, Nonrecurring [Table Text Block] Commercial loans Commercial Portfolio Segment [Member] Number of modifications (modification) Financing Receivable, Modifications, Number of Contracts Pre-Modification Outstanding Recorded Investment Financing Receivable, Troubled Debt Restructuring, Premodification Post-Modification Outstanding Recorded Investment Financing Receivable, Troubled Debt Restructuring, Postmodification Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] 2018 Equity Compensation Plan Equity Compensation Plan 2018 [Member] Equity Compensation Plan 2018 [Member] Restricted Stock Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Number of shares authorized under the plan (shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Number of shares counted against the share limit for each stock granted (percent) Share Based Compensation Arrangement by Share Based Payment Award Rate of Shares Counted Against Share Limit for Each Share Granted Represents the rate of shares counted as equivalent to each share award granted under a share-based compensation plan for the purpose of calculating the number of shares issued against the plan limit. Number of shares available for grant under the plan (shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Total compensation cost Share-based Payment Arrangement, Expense Total recognized tax benefit Share-based Payment Arrangement, Expense, Tax Benefit Weighted average fair value of stock awards granted (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Total fair value of awards vested Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Expected weighted-average period for recognition of unrecognized compensation Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Contractual life Share Based Compensation Arrangement by Share Based Payment Award Expiration Term Represents the period of time from the grant date until the time at which the share-based award expires. Weighted average remaining contractual term for options outstanding Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Total intrinsic value Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value Unrecognized stock-based compensation expense Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount Derivative Instruments and Hedging Activities Disclosure [Abstract] Schedule of Interest Rate Swap Agreements and Non-hedging Derivative Assets and Liabilities Schedule of Derivative Instruments [Table Text Block] Schedule of Amounts Included in the Consolidated Statements of income and in Other Comprehensive Income Schedule of Cash Flow Hedges Included in Accumulated Other Comprehensive Income (Loss) [Table Text Block] Schedule of Amounts Included in the Consolidated Statements of Income Related to Economic Hedges and Non-hedging Derivatives Derivative Instruments, Gain (Loss) [Table Text Block] Schedule of Assets Subject to an Enforceable Master Netting Arrangement Offsetting Assets [Table Text Block] Schedule of Liabilities Subject to an Enforceable Master Netting Arrangement Offsetting Liabilities [Table Text Block] Commercial real estate loans Individually evaluated for impairment Financing Receivable, Individually Evaluated for Impairment Purchased credit-impaired loans Financing Receivable, Purchased Credit-Impaired Loans Financing Receivable, Purchased Credit-Impaired Loans Collectively evaluated Financing Receivable, Collectively Evaluated for Impairment Total loans Loans and Leases Receivable, Net of Deferred Income Reclassification out of Accumulated Other Comprehensive Income [Table] Reclassification out of Accumulated Other Comprehensive Income [Table] Realized gains/(losses) on AFS securities Net (loss) on effective cash flow hedging derivatives Realized (losses) on pension plans Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income Reclassification out of Accumulated Other Comprehensive Income [Member] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Non-interest income Noninterest Income Interest expense Non-interest expense Interest Income (Expense), Net Tax expense (benefit) NET INTEREST INCOME AFTER PROVISION FOR LOAN LOSSES Interest Income and Interest Expense Disclosure [Text Block] Eastern Connecticut Eastern Connecticut [Member] Eastern Connecticut [Member] Rhode Island RHODE ISLAND Number of branch banking offices Number of Branch Banking Offices Number of Branch Banking Offices Equity interest issued or issuable, shares converted (in shares) Business Acquisition, Equity Interest Issued Or Issuable, Shares Converted Business Acquisition, Equity Interest Issued Or Issuable, Share Exchanged Equity interest, share exchange ratio Business Acquisition, Equity Interest Issued Or Issuable, Share Conversion Ratio Business Acquisition, Equity Interest Issued Or Issuable, Share Conversion Ratio Business acquisition, equity interest issued (shares) Business Acquisition, Equity Interest Issued or Issuable, Number of Shares Company common stock issued to SIFI common shareholders Business Combination, Consideration Transferred, Equity Interests Issued and Issuable Equity interest issued or issuable, basis for determining value, share price (in dollars per share) Business Acquisition, Equity Interest Issued Or Issuable, Basis For Determining Value, Share Price Business Acquisition, Equity Interest Issued Or Issuable, Basis For Determining Value, Share Price Fair value of SIFI stock options converted to Berkshire options Business Combination, Consideration Transferred, Equity Interests Issuable Business Combination, Consideration Transferred, Equity Interests Issuable Direct acquisition and integration costs Business Combination, Integration Related Costs Pro forma estimated tax rate Business Acquisition, Pro Forma Estimated Tax Rate Business Acquisition, Pro Forma Estimated Tax Rate Financing Receivable, Past Due [Table] Financing Receivable, Past Due [Table] Financial Asset, Period Past Due [Axis] Financial Asset, Period Past Due [Axis] Financial Asset, Period Past Due [Domain] Financial Asset, Period Past Due [Domain] 30-59 Days Past Due Financial Asset, 30 to 59 Days Past Due [Member] 60-89 Days Past Due Financial Asset, 60 to 89 Days Past Due [Member] 90 Days Past Due Financial Asset, Equal to or Greater than 90 Days Past Due [Member] Auto and other Auto And Other Receivable [Member] Class of financing receivables related to auto and other financing receivables. Financing Receivable, Past Due [Line Items] Financing Receivable, Past Due [Line Items] Total Past Due Financing Receivable, Past Due Acquired Credit Impaired Financing Receivable, Not Past Due Past Due greater than 90 days and Accruing Financing Receivable, 90 Days or More Past Due, Still Accruing Accounting Standards Update 2016-01 Accounting Standards Update 2016-01 [Member] Accounting Standards Update 2018-02 Accounting Standards Update 2018-02 [Member] Net unrealized holding gain (loss) on AFS securities Net unrealized holding gain on pension plans Gains (losses) arising during the period Other Comprehensive Income (Loss) before Reclassifications [Abstract] Before Tax OCI, before Reclassifications, before Tax, Attributable to Parent Tax Effect Other Comprehensive Income (Loss) before Reclassifications, Tax Net of Tax Less: reclassification adjustment for gains realized in net income Reclassification from Accumulated Other Comprehensive Income Current Period [Abstract] Before Tax Reclassification from AOCI, Current Period, before Tax, Attributable to Parent Tax Effect Reclassification from AOCI, Current Period, Tax Net of Tax Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Total other comprehensive income/(loss), before tax Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent Total income tax (expense) benefit related to other comprehensive income (loss) Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent Less: reclassification related to adoption of ASU Reclassification From AOCI, Accounting Standards Update [Abstract] Reclassification From AOCI, Accounting Standards Update [Abstract] Before Tax Reclassification From AOCI, Accounting Standards Update, Current Period, Before Tax, Attributable To Parent Reclassification From AOCI, Accounting Standards Update, Current Period, Before Tax, Attributable To Parent Tax Effect Reclassification From AOCI, Accounting Standards Update, Current Period, Tax Reclassification From AOCI, Accounting Standards Update, Current Period, Tax Net of Tax Total change to accumulated other comprehensive (loss) AOCI Attributable to Parent [Abstract] Before Tax Total Change To AOCI Before Tax, Attributable To Parent Total Change To AOCI Before Tax, Attributable To Parent Tax Effect Total Change To AOCI Tax, Attributable To Parent Total Change To AOCI Tax, Attributable To Parent Net of Tax Total Change To AOCI Net Of Tax, Attributable To Parent Total Change To AOCI Net Of Tax, Attributable To Parent Deposits [Abstract] DEPOSITS Deposit Liabilities Disclosures [Text Block] Statement of Stockholders' Equity [Abstract] Offering costs Payments of Stock Issuance Costs Cash dividends declared, common stock (USD per share) Common Stock, Dividends, Per Share, Declared Cash dividends declared, preferred stock (USD per share) Preferred Stock, Dividends Per Share, Declared Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Table] Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Table] Schedule of information required and determined to be provided for purposes of reconciling beginning and ending balances of fair value measurements of assets and liabilities using significant unobservable inputs (level 3). Such reconciliation, separately presenting changes during the period, at a minimum, may include, but is not limited to: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets) and gains or losses recognized in other comprehensive income, and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of level 3 (for example, transfers due to changes in the observability of significant inputs), by class of asset and liabilities. Asset Class [Axis] Asset Class [Axis] Asset Class [Domain] Asset Class [Domain] Trading Security Trading Assets, Excluding Debt and Equity Securities [Member] Securities Available for Sale Available-for-sale Securities [Member] Capitalized servicing rights Capitalized Mortgage Servicing Rights [Member] Represents the details pertaining to capitalized mortgage servicing rights. Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Commitments to Lend Commitments to Extend Credit [Member] Forward Contracts Forward Contracts [Member] Changes in Level 3 assets and liabilities that were measured at fair value on a recurring basis Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Changes in Level 3 assets that were measured at fair value on a recurring basis Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Balance at the beginning of the period Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Unrealized (loss), net recognized in other non-interest income Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings Unrealized gain/(loss), net recognized in discontinued operations Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings Unrealized (loss) included in accumulated other comprehensive loss Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss) Transfers to Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 Paydown of trading security Accretion (Amortization) of Discounts and Premiums, Investments Transfers to loans held for sale Transfer of Portfolio Loans and Leases to Held-for-sale Additions to servicing rights Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, (Sales), Issuances, (Settlements) Balance at the end of the period Unrealized gains (losses) relating to instruments still held at the end of the period Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings Related to Assets Still Held This element represents the total unrealized net gains included in net income related to assets still held as of the balance sheet date. Net interest income Business Acquisition, Pro Forma Interest Income (Expense), Net Business Acquisition, Pro Forma Interest Income (Expense), Net Non-interest income Business Acquisition, Pro Forma Noninterest Income Business Acquisition, Pro Forma Noninterest Income Income available to common shareholders Business Acquisition, Pro Forma Net Income (Loss) Available To Common Stockholders, Basic Business Acquisition, Pro Forma Net Income (Loss) Available To Common Stockholders, Basic Property, Plant and Equipment [Abstract] PREMISES AND EQUIPMENT Property, Plant and Equipment Disclosure [Text Block] Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table] Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table] Subsidiaries Subsidiaries [Member] Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] Capital [Abstract] Capital [Abstract] Total capital to risk-weighted assets, actual amount Capital Total capital to risk-weighted assets, actual percent Capital to Risk Weighted Assets Total capital to risk-weighted assets, minimum capital requirement, amount Capital Required for Capital Adequacy Total capital to risk-weighted assets, minimum capital requirement, percent Capital Required for Capital Adequacy to Risk Weighted Assets Total capital to risk-weighted assets, minimum to be well capitalized under prompt corrective action provisions, amount Capital Required to be Well Capitalized Total capital to risk-weighted assets, minimum to be well capitalized under prompt corrective action provisions, percent Capital Required to be Well Capitalized to Risk Weighted Assets Common Equity Tier One Capital [Abstract] Common Equity Tier One Capital [Abstract] Common Entity Tier 1 Capital to risk-weighted assets, amount Common Equity Tier One Risk Based Capital to Risk Weighted Assets, Amount Common Equity Tier One Risk Based Capital to Risk Weighted Assets, Amount Common Entity Tier 1 Capital to risk-weighted assets, percent Common Equity Tier One Risk Based Capital to Risk Weighted Assets Common equity Tier 1 capital divided by risk weighted assets as defined by regulations. Common Equity Tier 1 Capital to risk weighted assets, minimum capital requirement, amount Common Equity Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets, Amount Common Equity Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets, Amount Common Equity Tier 1 Capital to risk weighted assets, minimum capital requirement, percent Common Equity Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets The Common equity Tier 1 capital ratio (Common equity Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action. Common Entity Tier 1 Capital to risk-weighted assets, amount Common Entity Tier 1 Capital To Risk Weighted Assets, Capital Required to be Well Capitalized Common Entity Tier 1 Capital To Risk Weighted Assets, Capital Required to be Well Capitalized Common Entity Tier 1 Capital to risk-weighted assets, percent Common Entity Tier 1 Capital To Risk Weighted Assets, Capital Required to be Well Capitalized, Percent Common Entity Tier 1 Capital To Risk Weighted Assets, Capital Required to be Well Capitalized, Percent Tier One Risk Based Capital [Abstract] Tier One Risk Based Capital [Abstract] Tier 1 capital risk-weighted assets, amount Tier One Risk Based Capital Tier 1 capital risk-weighted assets, percent Tier One Risk Based Capital to Risk Weighted Assets Tier 1 capital risk-weighted assets, minimum capital requirement, amount Tier One Risk Based Capital Required for Capital Adequacy Tier 1 capital risk-weighted assets, minimum capital requirement, percent Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets Tier 1 capital risk-weighted assets, minimum to be well capitalized under prompt corrective action provisions, amount Tier One Risk Based Capital Required to be Well Capitalized Tier 1 capital risk-weighted assets, minimum to be well capitalized under prompt corrective action provisions, percent Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets Tier One Leverage Capital [Abstract] Tier One Leverage Capital [Abstract] Tier 1 capital to average assets, amount Tier One Leverage Capital Tier 1 capital to average assets, percent Tier One Leverage Capital to Average Assets Tier 1 capital to average assets, minimum capital requirement, amount Tier One Leverage Capital Required for Capital Adequacy Tier 1 capital to average assets, minimum capital requirement, percent Tier One Leverage Capital Required for Capital Adequacy to Average Assets Tier 1 capital to average assets, minimum to be well capitalized under prompt corrective action provisions, amount Tier One Leverage Capital Required to be Well Capitalized Tier 1 capital to average assets, minimum to be well capitalized under prompt corrective action provisions, percent Tier One Leverage Capital Required to be Well Capitalized to Average Assets Equity [Abstract] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Series B Convertible Preferred Stock Convertible Preferred Stock [Member] Class of Stock [Line Items] Class of Stock [Line Items] Shares issued upon conversion (shares) Convertible Preferred Stock, Shares Issued upon Conversion Preferred stock issued (shares) Preferred Stock, Shares Issued Preferred stock, shares outstanding (shares) Preferred Stock, Shares Outstanding Amortized Cost Security Owned and Pledged as Collateral Amortized Cost [Abstract] Securities pledged to swap counterparties Security Owned and Pledged as Collateral for Interest Rate Swap Amortized Cost 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. Securities pledged for municipal deposits Security Owned and Pledged as Collateral for Municipal Deposits Amortized Cost Represents the cost of financial instrument held by the entity for its own account (proprietary securities) and pledged for municipal deposits. Securities pledged, amortized cost Security Owned and Pledged as Collateral Amortized Cost Represents the cost of financial instrument held by the entity for its own account (proprietary securities). Fair Value Security Owned and Pledged as Collateral, Fair Value [Abstract] Securities pledged to swap counterparties Security Owned and Pledged as Collateral for Interest Rate Swap Fair Value 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. Securities pledged for municipal deposits Security Owned and Pledged as Collateral for Municipal Deposits Fair Value 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. Securities pledged, fair value Security Owned and Pledged as Collateral, Fair Value Components of net realized gains and losses on the sale of AFS securities Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract] Gross recognized gains Debt Securities, Available-for-sale, Realized Gain Gross recognized losses Debt Securities, Available-for-sale, Realized Loss, Excluding Other-than-temporary Impairment Net recognized gains/(losses) Debt Securities, Available-for-sale, Realized Gain (Loss), Excluding Other-than-temporary Impairment Statement of Financial Position [Abstract] Statement [Table] Statement [Table] Statement [Line Items] Statement [Line Items] Fair Value Preferred stock, par value (USD per share) Preferred Stock, Par or Stated Value Per Share Preferred stock, shares authorized (shares) Preferred Stock, Shares Authorized Preferred stock, shares issued (shares) Preferred stock, shares outstanding (shares) Common stock, par value (USD per share) Common Stock, Par or Stated Value Per Share Common stock, shares authorized (shares) Common Stock, Shares Authorized Common stock, shares issued (shares) Common Stock, Shares, Issued Common stock, shares outstanding (shares) Common Stock, Shares, Outstanding Treasury stock, shares (shares) Treasury Stock, Shares Assets Disposal Group, Including Discontinued Operation, Assets [Abstract] Loans held for sale, at fair value Disposal Group, Including Discontinued Operation, Loans Receivable Held-for-sale, Net Disposal Group, Including Discontinued Operation, Loans Receivable Held-for-sale, Net Premises and equipment, net Disposal Group, Including Discontinued Operation, Property, Plant and Equipment Mortgage servicing rights, at fair value Disposal Group, Including Discontinued Operation, Mortgage Servicing Rights At Fair Value Disposal Group, Including Discontinued Operation, Mortgage Servicing Rights At Fair Value Mortgage banking derivatives Disposal Group, Including Discontinued Operation, Mortgage Banking Derivatives Disposal Group, Including Discontinued Operation, Mortgage Banking Derivatives Right-of-use asset Disposal Group, Including Discontinued Operation, Operating Lease, Right-of-Use Asset Disposal Group, Including Discontinued Operation, Operating Lease, Right-of-Use Asset Deferred tax Disposal Group, Including Discontinued Operation, Deferred Tax Assets Other assets Disposal Group, Including Discontinued Operation, Other Assets Total assets Disposal Group, Including Discontinued Operation, Assets Liabilities Disposal Group, Including Discontinued Operation, Liabilities [Abstract] Customer payments in process Disposal Group, Including Discontinued Operation, Customer Payments In Process Disposal Group, Including Discontinued Operation, Customer Payments In Process Lease liability Disposal Group, Including Discontinued Operation, Lease, Liability Disposal Group, Including Discontinued Operation, Lease, Liability Other liabilities Disposal Group, Including Discontinued Operation, Other Liabilities Total liabilities Disposal Group, Including Discontinued Operation, Liabilities Weighted Average Weighted Average [Member] Measurement Input Type [Axis] Measurement Input Type [Axis] Measurement Input Type [Domain] Measurement Input Type [Domain] Loss severity Measurement Input, Loss Severity [Member] Appraised value Measurement Input, Appraised Value [Member] CPR Measurement Input, Constant Prepayment Rate [Member] Discount rate Measurement Input, Discount Rate [Member] Valuation Approach and Technique [Axis] Valuation Approach and Technique [Axis] Valuation Approach and Technique [Domain] Valuation Approach and Technique [Domain] Fair value of collateral Fair Value Of Collateral Valuation Technique [Member] Fair value of collateral approach valuation technique used to measure fair value. Discounted Cash Flow Valuation Technique, Discounted Cash Flow [Member] Impaired loans Total Assets Impaired loans Impaired Financing Receivables, Measurement Input Impaired Financing Receivables, Measurement Input Capitalized servicing rights Servicing Asset, Measurement Input LEASES Lessee, Operating Leases [Text Block] LEASES Lessee, Finance Leases [Text Block] Investment Holdings [Table] Investment Holdings [Table] Debt securities Debt Securities [Member] Investment Type [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] Agency collateralized mortgage obligations Collateralized Debt Obligations [Member] Municipal bonds and obligations US States and Political Subdivisions Debt Securities [Member] Agency residential mortgage-backed securities Residential Mortgage Backed Securities Guaranteed By U S Government [Member] Debt securities collateralized by residential real estate mortgage loans, guaranteed by US Government. Agency commercial mortgage-backed securities Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] Corporate bonds Corporate Bond Securities [Member] Tax advantaged economic development bonds Tax Advantaged Economic Development Bonds [Member] Represents the information pertaining to the tax advantaged economic development bonds. Other bonds and obligations Other Debt Obligations [Member] Investment Holdings [Line Items] Investment Holdings [Line Items] Securities available for sale Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] Less than twelve months, gross unrealized losses Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Less than twelve months, fair value Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months Over twelve months, gross unrealized losses Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Over twelve months, fair value Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer Total gross unrealized losses Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss Total fair value Debt Securities, Available-for-sale, Unrealized Loss Position Securities held to maturity Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract] Less than twelve months, gross unrealized losses Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Less than twelve months, fair value Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value Over twelve months, gross unrealized losses Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Over twelve months, fair value Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value Total gross unrealized losses Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss Total fair value Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value Securities available for sale and held to maturity Debt Securitives, Held To Maturity Securities and Available For Sale Securities, Continuous Unrealized Loss Position [Abstract] Less than twelve months, gross unrealized losses Debt Securities, Held to Maturity and Available for Sale Securities, Continuous Unrealized Loss Position, Less than 12 Months Aggregate Losses Represents the excess of amortized cost basis over the fair value of securities that have been in a loss position for less than twelve months for those securities that are categorized as held-to-maturity and available-for-sale. Less than twelve months, fair value Debt Securities, Held to Maturity and Available for Sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months Fair Value Represents the aggregate fair value of investments in debt and equity securities categorized as held-to-maturity and available-for-sale that have been in a continuous unrealized loss position for less than twelve months. Over twelve months, gross unrealized losses Debt Securities, Held to Maturity and Available for Sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer Aggregate Losses Represents the excess of amortized cost basis over the fair value of securities that have been in a loss position for twelve months or longer for those securities that are categorized as held-to-maturity and available-for-sale. Over twelve months, fair value Debt Securities, Held to Maturity and Available for Sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer Fair Value Represents the aggregate fair value of investments in debt and equity securities categorized as held-to-maturity and available-for-sale that have been in a continuous unrealized loss position for twelve months or longer. Total gross unrealized losses Debt Securities, Held to Maturity and Available for Sale Securities, Continuous Unrealized Loss Position Aggregate Losses Represents the excess of amortized cost basis over the fair value of securities that have been in a loss position, which are categorized as held-to-maturity and available-for-sale. Total fair value Debt Securities, Held to Maturity and Available for Sale Securities, Continuous Unrealized Loss Position, Fair Value Represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized as held-to-maturity and available-for-sale securities. Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Other Liabilities Other Liabilities [Member] Liability, Defined Benefit Plan Liability, Defined Benefit Plan Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] Unrecognized tax benefits at January 1 Unrecognized Tax Benefits Increase in gross amounts of tax positions related to prior years Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions Decrease in gross amounts of tax positions related to prior years Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions Decrease due to settlement with taxing authority Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities Increase in gross amounts of tax positions related to current year Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions Decrease due to lapse in statute of limitations Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations Unrecognized tax benefits at December 31 Derivative [Table] Derivative [Table] Hedging Designation [Axis] Hedging Designation [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Hedging derivatives Designated as Hedging Instrument [Member] Non-hedging derivatives Not Designated as Hedging Instrument [Member] Hedging Relationship [Axis] Hedging Relationship [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Economic Hedging Economic Hedging [Member] Represents information pertaining to derivatives that are not designated as accounting hedges but are being used as economic hedges. Interest Rate Swap Interest Rate Swap [Member] Reverse Interest Rate Swaps Reverse Interest Rate Swaps [Member] Represents information pertaining to the reverse interest rate swaps which can be used to synthetically convert fixed rate debt to floating. Risk Participation Agreements Risk Participation Agreements [Member] Represents the information pertaining to risk participation agreements with dealer banks. Forward Commitments Forward Commitments [Member] Represents the forward commitments that are free-standing derivatives which are carried at fair value with changes recorded in the mortgage banking component of noninterest income in the entity's consolidated statements of income. Liability Class [Axis] Liability Class [Axis] Fair Value by Liability Class [Domain] Fair Value by Liability Class [Domain] Industrial Revenue Bond Industrial Revenue Bond [Member] Represents information pertaining to the industrial revenue bond, a financing instrument issued by designated local industrial development boards (IDB's) or other issuers authorized by state law. Commercial loan Commercial Paper [Member] Derivative [Line Items] Derivative [Line Items] Unrealized gain (loss) recognized in other non-interest income Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments (Unfavorable)/Favorable change in credit valuation adjustment recognized in other non-interest income Derivative Instruments Favorable Changes in Credit Valuation Adjustment Recognized in Other Non Interest Income The favorable changes in credit valuation adjustments on derivative instruments that were recognized in other non-interest income during the current period. Realized (loss) in discontinued operations Gain (Loss) on Sale of Derivatives Debt Security Category [Axis] Debt Security Category [Axis] Other than Temporary Impairment, Credit Losses Recognized in Earnings, Categories of Investments [Domain] Other than Temporary Impairment, Credit Losses Recognized in Earnings, Categories of Investments [Domain] Held-to-maturity Securities Held-to-maturity Securities [Member] Collateralized mortgage obligations Collateralized Mortgage Obligations [Member] Mortgage-backed Securities Residential Mortgage Backed Securities [Member] Other accumulated comprehensive income/(loss), before tax AOCI Including Portion Attributable to Noncontrolling Interest, before Tax Income tax benefit/(liability) related to items of accumulated other comprehensive income/(loss) Accumulated Other Comprehensive Income (Loss) Tax Tax effect of accumulated other comprehensive income (loss). Purchases of securities available for sale Payments to Acquire Debt Securities, Available-for-sale Proceeds from sales of securities available for sale Proceeds from Sale of Debt Securities, Available-for-sale Available-for-sale securities in an unrealized loss position (security) Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions Available for sale securities portfolio, number of securities (security) Debt Securities, Available for Sale Securities Portfolio Number of Securities Represents the number of securities in the entity's portfolio of available-for-sale securities. Aggregate unrealized losses as a percentage of the amortized cost of the securities in unrealized loss positions Debt Securities, Continuous Unrealized Loss Position, Qualitative Disclosure, Aggregate Losses Percentage Represents the aggregate unrealized losses, expressed as a percentage of the amortized cost of the securities in a continuous unrealized loss position categorized as held-to-maturity and available-for-sales securities. Number of HTM investment securities in unrealized loss positions (security) Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions Number of securities in the portfolio of HTM (security) Held-to-maturity, Securities Portfolio Number of Securities Held-to-maturity, Securities Portfolio Number of Securities Agency collateralized mortgage obligations Agency mortgage-backed securities Corporate bonds Securities available for sale Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract] Amortized Cost Debt Securities, Available-for-sale, Amortized Cost Gross Unrealized Gains Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax Gross Unrealized Losses Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax Securities available for sale, at fair value Securities held to maturity Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract] Amortized Cost Debt Securities, Held-to-maturity Gross Unrealized Gains Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain Gross Unrealized Losses Marketable equity securities, amortized cost Equity Securities, FV-NI, Cost Marketable equity securities, gross unrealized gains Equity Securities, FV-NI, Unrealized Gain Marketable equity securities, gross unrealized losses Equity Securities, FV-NI, Unrealized Loss Marketable equity securities, fair value Amortized Cost Debt Securities, Available-for-sale and Held-to-maturity, and Equity Securities, FV-NI, Amortized Cost Represents the cost of debt and equity securities, which are categorized as held-to-maturity and available-for-sale, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. Gross Unrealized Gains Debt Securities, Available-for-sale and Held-to-maturity, and Equity Securities, FV-NI, Accumulated Gross Unrealized Gain, before Tax Represents the gross unrealized gains for securities, at a point in time, which are categorized as held-to-maturity and available-for-sale securities. Gross Unrealized Losses Debt Securities, Available-for-sale and Held-to-maturity, and Equity Securities, FV-NI, Accumulated Gross Unrealized Loss, before Tax Represents the gross unrealized losses for securities, at a point in time, which are categorized as held-to-maturity and available-for-sale securities. Fair Value Debt Securities, Available-for-sale and Held-to-maturity, and Equity Securities, FV-NI Debt Securities, Available-for-sale and Held-to-maturity, and Equity Securities, FV-NI Summary of Premises and Equipment Property, Plant and Equipment [Table Text Block] Offsetting Assets [Table] Offsetting Assets [Table] Economic hedges Interest rate swap Reverse interest rate swaps Risk participation agreements Forward Sale commitments Tax advantaged economic development bonds Nontaxable Municipal Bonds [Member] Offsetting Assets [Line Items] Offsetting Assets [Line Items] Notional Amount Derivative, Notional Amount Weighted Average Maturity Derivative, Average Remaining Maturity Derivative, weighted average rate, received (percent) Derivative, Weighted Average Rate, Received Represents information pertaining to the derivative weighted average rate which is received. Derivative, weighted average rate, contract pay rate (percent) Derivative, Weighted Average Rate, Paid Represents information pertaining to the derivative weighted average rate which is paid. Estimated Fair Value Asset (Liability) Derivative Assets (Liabilities), at Fair Value, Net Projected benefit obligation, discount rate Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate Net periodic pension cost, discount rate Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate Net periodic pension cost, long term rate of return on plan assets Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] Affiliated Entity Affiliated Entity [Member] Related Party Transaction [Line Items] Related Party Transaction [Line Items] Brokered deposits Brokered Time Deposits Represents the amount of time deposits placed by or through the assistance of a deposit broker, also known as brokered deposit liabilities. Reciprocal deposits Reciprocal Money Market Deposits Represents the reciprocal deposits. Time deposits Time Deposits Non-vested Stock Awards Outstanding, Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Balance at the beginning of the period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Stock awards vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Balance at the end of the period (in shares) Non-vested Stock Awards Outstanding, Weighted-Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Balance at the beginning of the period (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Granted (USD per share) Stock awards vested (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Forfeited (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Balance at the end of the period (USD per share) Stock Options Outstanding, Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Balance at the beginning of the period (shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Granted (shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Acquired (shares) Share-based Compensation Arrangement By Share-based Payment Award, Options, Acquired In Period Share-based Compensation Arrangement By Share-based Payment Award, Options, Acquired In Period Exercised (shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Forfeited (shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period Expired (shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period Balance at the end of the period (shares) Stock Options Outstanding, Weighted-Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Balance at the beginning of the period (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Granted (USD per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Acquired (USD per share) Share-based Compensation Arrangements By Share-based Payment Award, Options, Acquired In Period, Weighted Average Exercise Price Share-based Compensation Arrangements By Share-based Payment Award, Options, Acquired In Period, Weighted Average Exercise Price