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Savings Deposits, Savings Deposits Purchases of BOLI policies Payment to Acquire Life Insurance Policy, Investing Activities Net gain on sale of mortgage loans Net gain on sale of mortgage loans Gain (Loss) on Sale of Mortgage Loans Banking Regulation, Regulatory Capital Requirement, Compliance [Table] Banking Regulation, Regulatory Capital Requirement, Compliance [Table] Grand River Grand River [Member] Grand River Risk ratings 1-3 Risk Ratings 1-3 [Member] Risk Ratings 1-3 Allowance for credit losses ACL, excluding accrued interest, beginning balance ACL, excluding accrued interest, beginning balance Total Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest All Other AFS Securities Available-for-sale Securities, Excluding Auction Rate Money Market Preferred and Preferred Stocks [Member] Available-for-sale Securities, Excluding Auction Rate Money Market Preferred and Preferred Stocks [Member] Financing receivable, excluding accrued interest, year three, originated, two years before current fiscal year Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year Document Period End Date Document Period End Date Net changes in: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Net cash provided by investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] Isabella Bank Subsidiaries [Member] Principal Debt Instrument, Face Amount Revolving Loans Converted to Term Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan Capital Ratios and Shareholders' Equity Equity [Text Block] Security Exchange Name Security Exchange Name Increase in the cash surrender value of BOLI, net of expenses Bank Owned Life Insurance Income, Net of Expense Bank Owned Life Insurance Income, Net of Expense Total capital to risk weighted assets, Minimum Capital Required Plus Capital Conservation Buffer, Ratio Capital Required For Capital Adequacy To Risk Weighted Assets Minimum Capital Required Plus Capital Conservation Buffer Capital Required For Capital Adequacy To Risk Weighted Assets Minimum Capital Required Plus Capital Conservation Buffer Tax effect Tax effect OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax Debt Securities, Available-for-sale, Maturity, Fair Value, Rolling Maturity [Abstract] Debt Securities, Available-for-Sale, Maturity, Fair Value, Rolling Maturity [Abstract] Valuation Approach and Technique [Axis] Valuation Approach and Technique [Axis] Total Financing Receivable, before Allowance for Credit Loss Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Entity Shell Company Entity Shell Company Interest bearing demand deposits Interest-Bearing Domestic Deposit, Demand Other assets Interest Receivable and Other Assets Fair Value, Twelve Months or More Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer Operating Segments Segment Reporting, Policy [Policy Text Block] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] After Five Years But Within Ten Years Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling after 5 through 10 Years, Amortized Cost Foreclosed assets Foreclosed Assets, Fair Value Disclosure Foreclosed Assets, Fair Value Disclosure Computation of Earnings Per Common Share Earnings Per Share [Text Block] Name Outstanding Recovery, Individual Name Share-based payment awards under the Directors Plan Deferred Compensation Arrangement with Individual, Deferred Fees Contribution Share based payment awards under equity compensation plan. 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