Document And Entity Information us-gaap_PaymentsForProceedsFromLoansAndLeases Net Loans to Customers Financing Receivables, Equal to Greater than 90 Days Past Due [Member] Note To Financial Statement Details Textual Significant Accounting Policies Note 1 - Summary of Significant Accounting Policies Interest-Bearing Deposits in Other Banks Note 2 - Cash and Balances Due From Banks Interest Expense Property, plant and equipment, depreciation method Description of the methodology for computing depreciation for classes of depreciable assets. Financing Receivables, Period Past Due [Domain] London Interbank Offered Rate (LIBOR) [Member] Note 3 - Investment Securities Financing Receivables, Period Past Due [Axis] Note 4 - Loans Note 5 - Allowance for Loan Losses Variable Rate [Domain] Note 6 - Premises and Equipment Variable Rate [Axis] Note 7 - Other Real Estate Owned us-gaap_AvailableForSaleSecuritiesDebtSecurities Fair value Prime Rate [Member] Note 8 - Other Intangible Assets Past Due Financing Receivables [Table Text Block] Note 9 - Income Taxes Note 10 - Deposits Dividends from Subsidiary Note 11 - Other Borrowed Money Note 12 - Subordinated Debentures (Trust Preferred Securities) Schedule of Long-term Debt Instruments [Table Text Block] Note 15 - Commitments and Contingencies us-gaap_InterestAndDividendIncomeOperating Note 17 - Supplemental Cash Flow Information Note 18 - Related Party Transactions Deposits with Other Banks us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromFourToFiveYearsOfBalanceSheetDate 2022 Note 19 - Fair Value of Financial Instruments and Fair Value Measurements Dividends on Other Investments Note 20 - Regulatory Capital Matters Available for sale securities, fair value Investment Securities Available for Sale, at Fair Value Investment Securities Available for Sale Note 21 - Financial Information of Colony Bankcorp, Inc. (Parent Only) Note 22 - Earnings Per Share us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax Tax Effect Note 23 - Accumulated Other Comprehensive Income (Loss) us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesTax Tax Effect Note 1 - Summary of Significant Accounting Policies - Estimated Useful Lives and Methods of Depreciation (Details) Federal Funds Sold Tax Effect Tax Effect Note 2 - Cash and Balances Due from Banks - Cash and Balances Due From Banks (Details) Note 3 - Investment Securities - Schedule of Investment Securities (Details) Note 3 - Investment Securities - Amortized Cost and Fair Value of Investment Securities by Contractual Maturity (Details) us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresAmountOfAvailableUnusedFunds Federal Home Loan Bank, Advances, General Debt Obligations, Amount of Available, Unused Funds Note 3 - Investment Securities - Continuous Unrealized Loss Position (Details) Proceeds from Sale of Federal Home Loan Bank Stock Note 4 - Loans - Segregated by Class of Loans (Details) Corporate us-gaap_PaymentsToAcquireFederalHomeLoanBankStock Purchase of Federal Home Loan Bank Stock Note 4 - Loans - Loan Portfolio by Credit Quality Indicator (Details) Note 4 - Loans - Age Analysis of Past Due Loans and Nonaccrual Loans (Details) us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1 Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged Note 4 - Loans - Impaired Loan Data (Details) Note 4 - Loans - Modified in a Troubled Debt Restructuring (Details) us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Interest Rate at Period End Note 4 - Loans - Loans Modified in a Troubled Debt Restructuring (Details) us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresDueDateLast Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Due Date, Last us-gaap_InterestIncomeSecuritiesUSTreasuryAndOtherUSGovernment U.S. Government Agencies Note 5 - Allowance for Loan Losses - Changes in the Allowance for Loan Losses (Details) us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresDueDateEarliest Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Due Date, Earliest Note 5 - Allowance for Loan Losses - Segregated by Class of Loan (Details) Note 5 - Allowance for Loan Losses - Segregated by Impairment Methodology (Details) us-gaap_OtherOperatingActivitiesCashFlowStatement Other Note 6 - Premises and Equipment - Premises and Equipment (Details) us-gaap_InterestIncomeSecuritiesStateAndMunicipal State, County and Municipal Note 6 - Premises and Equipment - Future Minimum Rental Payments (Details) Cash Flows from Investing Activities Note 7 - Other Real Estate Owned - Change in OREO (Details) Note 8 - Other Intangible Assets - Analysis of the Core Deposit Intangible Activity (Details) us-gaap_LifeInsuranceCorporateOrBankOwnedChangeInValue Increase in Cash Surrender Value of Life Insurance Note 9 - Income Taxes - Components of Income Tax (Details) Reported Value Measurement [Member] Note 9 - Income Taxes - Difference Between Financial Statement Tax Expense and Amount Computed by Applying Statutory Federal Tax Rate to Income Before Income Taxes (Details) us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet Other Note 9 - Income Taxes - Deferred Tax Assets and Liabilities (Details) Note 10 - Deposits - Components of Interest-bearing Deposits (Details) Note 10 - Deposits - Scheduled Maturities of Certificates of Deposit (Details) Note 11 - Other Borrowed Money - Summary of Other Borrowed Money (Details) Note 11 - Other Borrowed Money - Aggregate Stated Maturities (Details) Note 12 - Subordinated Debentures (Trusted Preferred Securities) - Schedule of Subordinated Debentures (Details) Investment in Federal Home Bank Stock [Policy Text Block] Disclosure of accounting policy for investments in Federal Home Loan Bank Stock (FHLB) including how assets is carried on balance sheet and how interest revenue is recorded in statement of operations. Note 15 - Commitments and Contingencies - Financial Instruments Outstanding Whose Contract Amount Represents Credit Risk (Details) Bank Owned Life Insurance [Policy Text Block] Disclosure of accounting policy for bank-owned life insurance. Note 17 - Supplemental Cash Flow Information - Cash Payments (Details) Investment Securities Note 17 - Supplemental Cash Flow Information - Non-cash Financing and Investing Activities (Details) Loans, Including Fees Note 18 - Related Party Transactions - Activity of Related Party Loan (Details) Note 19 - Fair Value of Financial Instruments and Fair Value Measurements - Financial Instruments (Details) Note 19 - Fair Value of Financial Instruments and Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis (Details) Note 19 - Fair Value of Financial Instruments and Fair Value Measurements - Quantitative Information for Financial Instruments Measured at Fair Value (Details) Note 19 - Fair Value of Financial Instruments and Fair Value Measurements - Fair Value Measurement Using Significant Unobservable Inputs (Details) Note 19 - Fair Value of Financial Instruments and Fair Value Measurements - Quantitative Information About Recurring Level 3 Fair Value Measurement (Details) Note 20 - Regulatory Capital Matters - Summary of Regulatory Capital Information (Details) Note 21 - Financial Information of Colony Bankcorp, Inc. (Parent Only) - Balance Sheets, Parent Only (Details) Note 21 - Financial Information of Colony Bankcorp, Inc. (Parent Only) - Balance Sheets, Parent Only (Details) (Parentheticals) Comprehensive Income Comprehensive Income Accrued Expenses and Accounts Payable Note 21 - Financial Information of Colony Bankcorp, Inc. (Parent Only) - Statements of Operations, Parent Only (Details) Note 21 - Financial Information of Colony Bankcorp, Inc. (Parent Only) - Consolidated Statements of Comprehensive Income, Parent Company (Details) Note 21 - Financial Information of Colony Bankcorp, Inc. (Parent Only) - Statements of Cash Flows, Parent Company (Details) Note 22 - Earnings Per Share - Summary of Earnings Per Share (Details) Note 23 - Accumulated Other Comprehensive Income (Loss) - Changes for Unrealized Gains and Losses Securities Available for Sale (Details) Notes To Financial Statements Notes To Financial Statements [Abstract] us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity Line of Credit Facility, Current Borrowing Capacity Interest Payable Preferred stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding Use of Estimates, Policy [Policy Text Block] Cash and Cash Equivalents Disclosure [Text Block] Common stock, shares outstanding (in shares) Cash and Cash Equivalents New Accounting Pronouncements, Policy [Policy Text Block] Reclassification, Policy [Policy Text Block] us-gaap_SharesOutstanding Balance (in shares) Balance (in shares) us-gaap_CashDividendsPaidToParentCompanyByConsolidatedSubsidiaries Cash Dividends Paid to Parent Company by Consolidated Subsidiaries Interest Income Furniture and Equipment [Member] Equipment commonly used in offices and stores that have no permanent connection to the structure of a building or utilities. Examples include, but are not limited to, desks, chairs, tables, and bookcases. Banking Premises [Member] Facility held for productive use including, but not limited to, office, production, storage and distribution facilities. Consolidation, Policy [Policy Text Block] Commercial and Agricultural Portfolio Segment [Member] Portfolio segment of the company's total financing receivables related to commercial and agricultural receivables. Agricultural [Member] Loans related to agricultural receivables. Commercial [Member] Loan related to commercial receivables. Commercial Construction [Member] Loan related to commercial construction. Real Estate Portfolio Segment [Member] Portfolio segment of the company's total financing receivables related to real estate. Residential Construction [Member] Loans related to residential construction. us-gaap_SalesRevenueNet cban_DepreciatedDebtSecuritiesWithUnrealizedLosses Depreciated Debt Securities With Unrealized Losses Refers to the depreciated percentage of debt securities with unrealized losses measuring in amortized cost basis. us-gaap_CashAndCashEquivalentsAtCarryingValue Cash and Cash Equivalents, Beginning Cash and Cash Equivalents, Ending Farmland [Member] Loans related to farmland. Residential [Member] Loans relating to residential receivables. Consumer [Member] Loans related to consumer receivables. Consumer and Other Portfolio Segment [Member] Portfolio segment of the company's total financing receivables related to consumer and other receivables Cash and Due from Banks Other [Member] Loans not otherwise classified. us-gaap_DividendsPreferredStock Dividends on Preferred Shares us-gaap_DueFromBanks Noninterest-Bearing Deposits with Other Banks Cash Cash on Hand and Cash Items Interest-Bearing Deposits us-gaap_DividendsCommonStock Dividends on Common Shares us-gaap_OtherSalesRevenueNet Other us-gaap_FairValueInputsCapRate Fair value inputs, capitalization rate Debt Disclosure [Text Block] cban_ImpairedLoansFairValue Impaired Loans Fair value portion of impaired loans. cban_OtherRealEstateFairValue Other Real Estate Fair value portion of other real estate. Schedule of Other Significant Noncash Transactions [Table Text Block] Fair value inputs, discount rate Range Weighted Average Fair value inputs, comparability adjustments Redemption of Preferred Stock (in shares) Stock Redeemed or Called During Period, Shares Redemption of Preferred Stock (in shares) Valuation Technique [Domain] us-gaap_StockRedeemedOrCalledDuringPeriodValue Redemption of Preferred Stock Valuation Technique [Axis] Income Approach Valuation Technique [Member] Market Approach Valuation Technique [Member] ATM/Card Processing The amount of expense incurred in the period for ATM/Card Processing. us-gaap_TimeDepositMaturitiesYearTwo 2019 us-gaap_TimeDepositMaturitiesYearFour 2021 us-gaap_IncreaseDecreaseInPrepaidExpense Prepaid Expenses us-gaap_TimeDepositMaturitiesYearThree 2020 Change In us-gaap_TimeDepositMaturitiesYearOne 2018 Management Fees us-gaap_DepositLiabilitiesReclassifiedAsLoansReceivable1 Deposit Liabilities Reclassified as Loans Receivable Nature of Operations [Policy Text Block] Disclosure of accounting policy regarding the nature of an entity's business and its policies, the major products or services it sells or provides and its principal markets, including the locations of those markets. If the entity operates in more than one business, the disclosure also indicates the relative importance of its operations in each business and the basis for the determination (for example, assets, revenues, or earnings). Fair Value Inputs, Assets, Quantitative Information [Table Text Block] cban_NumberOfAssetBackedSecuritiesOwned Number of Asset Backed Securities Owned Refers to the number of asset-backed security owned by the entity. us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss Unrealized Gains(Losses) Included in Other Comprehensive Income cban_NumberOfIssuancesOfTrustPreferredSecurities Number of Issuances of Trust Preferred Securities Represents the umber of issuance of trust preferred securities. Ending loan balance, individually evaluated for impairment us-gaap_IncreaseDecreaseInAccruedInterestReceivableNet Interest Receivable Ending loan balance, collectively evaluated for impairment Ending allowance balance, collectively evaluated for impairment Loss on OTTI Impairment Included in Noninterest Income Ending allowance balance, individually evaluated for impairment us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery Recoveries of Loans Previously Charged Off us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs Loans Charged Off Financing Receivables, 30-89 Days Past Due [Member] Financing receivables that are less than 90 days past due but more than 29 days past due. Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Real Estate Owned, Valuation Allowance, Policy [Policy Text Block] Savings Cash Flow, Supplemental Disclosures [Text Block] Other Time Allowance for Credit Losses on Financing Receivables [Table Text Block] Time, $250,000 and Over Interest-Bearing Demand us-gaap_FinancingReceivableAllowanceForCreditLosses Balance, Beginning of Year Balance, End of Year Other Real Estate (Net of Allowance of $1,451,492 and $1,878,127 in 2017 and 2016, Respectively) Other Real Estate Balance, Beginning of Year Balance, End of Year Allowance for loan losses, recoveries us-gaap_OtherRealEstateAndForeclosedAssets Other Real Estate, Foreclosed Assets, and Repossessed Assets us-gaap_InterestBearingDomesticDepositBrokered Interest-bearing Domestic Deposit, Brokered us-gaap_TimeDepositsAtOrAboveFDICInsuranceLimit Time Deposits, at or Above FDIC Insurance Limit Deposit Liabilities Disclosures [Text Block] us-gaap_CashSurrenderValueOfLifeInsurance Cash Surrender Value of Life Insurance Total Liabilities and Stockholders’ Equity Total Liabilities and Stockholders’ Equity Retained Earnings Ending allowance balance Loans and Leases Receivable, Allowance Allowance for Loan Losses Allowance for loan losses, beginning balance Allowance for loan losses, ending balance us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs Allowance for loan losses, charge-offs us-gaap_LoansAndLeasesReceivableNetReportedAmount Accumulated Other Comprehensive Loss, Net of Tax Ending loan balance Loans Loans and Leases Receivable, Gross us-gaap_DeferredTaxAssetsNet us-gaap_LoansAndLeasesReceivableDeferredIncome Unearned Interest and Fees Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Marketable Securities [Table Text Block] us-gaap_NoninterestIncomeOtherOperatingIncome Other us-gaap_DeferredIncomeTaxLiabilities Schedule of Allowance for Loan Losses by Portfolio Segment [Table Text Block] Tabular disclosure of allocation of allowance for loan and lease losses by portfolio segment based on methodology used to evaluate loans and leases for impairment. us-gaap_NoninterestIncome us-gaap_DeferredTaxAssetsLiabilitiesNet Net Deferred Tax Assets Other Borrowings [Member] Relates to the Company's other borrowings, or to a line item by the name Other Borrowings. us-gaap_DeferredTaxAssetsOther Other Other Borrowings The carrying amount as of the balance sheet date for the other miscellaneous borrowings owed by the reporting entity excluding Federal Home Loan Bank advances. us-gaap_DeferredTaxAssetsInvestments Investments Policy Loans Receivable, Policy [Policy Text Block] us-gaap_BankOwnedLifeInsuranceIncome Bank Owned Life Insurance Income Noninterest Income us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss Net Interest Income After Provision for Loan Losses Allowance for loan losses, provision Provision for Loan Losses Provision for Loan Losses us-gaap_DeferredTaxAssetsGoodwillAndIntangibleAssets Goodwill us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 Transfers out of Level 3 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue Balance, available for sale securities Balance, available for sale securities Provision for Losses on Other Real Estate Transfers into Level 3 Securities Purchased During the Year us-gaap_InterestIncomeExpenseNet Net Interest Income us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales Securities Matured During the Year Mortgage Fee Income Federal Home Loan Bank Stock, at Cost Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Service Charges on Deposits us-gaap_CashCashEquivalentsAndFederalFundsSold Cash, Beginning Cash, Ending us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses Allowance for Loan Losses us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsOther Deferred Compensation us-gaap_DisclosureTextBlockAbstract Notes to Financial Statements Changes in the Allowance for Loan Losses [Table Text Block] Tabular disclosure of the changes during the period in the allowance for credit losses on financing receivables. Loans Not Classified as Impaired [Member] Represents loans not classified as impaired. cban_LoanBalanceForReviewingHighRiskLoansMinimum Loan Balance For Reviewing High Risk Loans Minimum Minimum loan balance for reviewing. cban_ImpairedFinancingReceivableRecordedInvestmentBelowReviewThreshold Impaired Financing Receivable Recorded Investment Below Review Threshold Amount of investment of impaired financing receivables below the $250,000 threshold for review and were not individually reviewed for impairment. Fair Value, Measurements, Nonrecurring [Member] Fair Value, Measurements, Recurring [Member] cban_IncomeBeforeEquityInUndistributedEarningsOfSubsidiary Income Before Equity in Undistributed Earnings of Subsidiary Income or Loss from continuing operations, net of taxes, including net Income or Loss from discontinued operations but before equity in undistributed earnings of subsidiary. Comprehensive Income, Policy [Policy Text Block] cban_AnnualRateOfAmortizationExpense Annual Rate of Amortization Expense Annual rate of amortization expense for intangible assets. Fair Value, Measurement Frequency [Domain] Measurement Frequency [Axis] Income Tax, Policy [Policy Text Block] cban_DeferredTaxAssetsOtherRealEstate Other Real Estate Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from other real estate. Dividends Received in Excess of Earnings of Subsidiary Dividends Received in Excess of Earnings of Subsidiary The amount of dividends received in excess of earnings of subsidiaries. Property, Plant and Equipment [Table Text Block] Deferred Tax Assets (Liabilities) on Unrealized Securities Gains (Losses) Amount before allocation of valuation allowances of deferred tax assets and liabilities attributable to deductible temporary differences from unrealized losses and gains on securities. Property, Plant and Equipment Disclosure [Text Block] Deferred Tax Assets Investment in Subsidiary, at Equity Other than Temporary Impairment, Credit Losses Recognized in Earnings, Categories of Investments [Domain] Debt Security Category [Axis] us-gaap_OperatingLeasesRentExpenseNet Operating Leases, Rent Expense, Net us-gaap_DeferredTaxLiabilitiesOther Other Deferred Income Taxes Interest Amendment Flag Other Borrowed Money us-gaap_FederalHomeLoanBankBorrowingsFairValueDisclosure Common Stock, Par Value $1; 20,000,000 Shares Authorized, 8,439,258 Shares Issued and Outstanding as of December 31, 2017 and 2016 Common stock, shares authorized (in shares) Subordinated Debentures us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations Common stock, shares issued (in shares) Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Common stock, par value (in dollars per share) Advertising Costs, Policy [Policy Text Block] Loss on Sale Gain (loss) on sale of other real estate excluding physical possession. Current Fiscal Year End Date cban_TimeDepositsMaturitiesYearFiveAndAfterYearFive 2022 and Thereafter Amount of time deposits maturing in the fifth fiscal year following the latest fiscal year and in years after the fifth fiscal year. Time deposits include, but are not limited to, certificates of deposits. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. cban_MinimumAgeRequirementForDeferredCompensation Minimum Age Requirement for Deferred Compensation This line item represents the minimum age requirement after which the entity is committed to pay deferred compensation.` Document Fiscal Period Focus Document Fiscal Year Focus cban_EmployeeServicePeriod Employee Service Period Represents minimum service period for employees to be fully vested in company contributions. Scheduled Maturities Of Certificates Of Deposits [Table Text Block] Tabular disclosure of certificates of deposits, classified with respect to their maturities as of balance sheet date. Deferred Tax Liabilities Document Period End Date us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments Amortization and Accretion Preferred Stock, Stated Value $1,000; 10,000,000 Shares Authorized, 0 and 9,360 Shares Issued and Outstanding as of December 31, 2017 and 2016 cban_FeeIncomeRecognizedWithDeferredCompensationPlans Fee Income Recognized With Deferred Compensation Plans Total fees and commissions earned from providing services such as leasing of space or maintaining: (1) depositor accounts; (2) transfer agent; (3) fiduciary and trust; (4) brokerage and underwriting; (5) mortgage; (6) credit cards; (7) correspondent clearing; and (8) other such services and activities performed for others. us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment Premises and Equipment Preferred stock, shares issued (in shares) Deferred Compensation Plan [Text Block] Disclosure of pension and other postretirement benefit arrangements with individual employees, which are generally based on employment contracts between the entity and one or more selected officers or key employees, and which contain a promise by the employer to pay certain amounts at designated future dates. Disclosure also typically includes the amount of related compensation expense recognized during the reporting period and the carrying amount as of the balance sheet date of the related liability. Document Type us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent Change in Unrealized Gains (Losses) on Securities Available for Sale, Net of Reclassification Adjustment and Tax Effects cban_LoansAndLeasesReceivableRelatedPartiesTransactionsDueToChangesInDirectors Transactions Due to Changes in Directors The reduction amount of loans and leases receivable due to changes in directors. Preferred stock, shares authorized (in shares) Preferred Stock And Warrants [Text Block] The entire disclosure for terms, amounts, nature of changes, rights and privileges, dividends, and other matters related to preferred stock and warrants. Document Information [Line Items] Document Information [Table] Preferred stock, stated value (in dollars per share) us-gaap_Depreciation Depreciation Entity Public Float Estimate of Fair Value Measurement [Member] Entity Filer Category Entity Current Reporting Status Entity Voluntary Filers Entity Well-known Seasoned Issuer Measurement Basis [Axis] Portion at Fair Value Measurement [Member] Colony Bankcorp Capital Trust I [Member] Colony Bankcorp Capital Trust I, a company controlled, directly or indirectly, by its parent, which has issued securities and those securities are guaranteed by its parent and another subsidiary of the parent. Colony Bankcorp Statutory Trust III [Member] Colony Bankcorp Statutory Trust III, a company controlled, directly or indirectly, by its parent, which has issued securities and those securities are guaranteed by its parent and another subsidiary of the parent. Colony Bankcorp Capital Trust II [Member] Colony Bankcorp Capital Trust II, a company controlled, directly or indirectly, by its parent, which has issued securities and those securities are guaranteed by its parent and another subsidiary of the parent. Deferred Tax Expense from Tax Rate Changes Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability Colony Bankcorp Capital Trust III [Member] Colony Bankcorp Capital Trust III, a company controlled, directly or indirectly, by its parent, which has issued securities and those securities are guaranteed by its parent and another subsidiary of the parent. us-gaap_PreferredStockRedemptionPricePerShare Preferred Stock, Redemption Price Per Share 5 year call option Minimum redemption date. 3 month LIBOR rate The rate which is used as a benchmark to determine the variable rates. Intangible Assets Disclosure [Text Block] cban_ExpirationPeriodOfLetterOfCreditIssued Expiration Period Of Letter Of Credit Issued Refers to the expiration dates of letter of credit issued measured in years. Adjustments to Reconcile Net Income to Net Cash Provided from Operating Activities Current State Income Tax Expense Entity Central Index Key us-gaap_FederalIncomeTaxExpenseBenefitContinuingOperations Federal Income Tax Expense (Benefit), Continuing Operations Federal Income Tax Expense Troubled Debt Restructurings That Subsequently Default [Table Text Block] Tabular disclosure of troubled debt restructurings that subsequently defaulted. Entity Registrant Name Summary Of Financial Instrument Outstanding [Table Text Block] Tabular disclosure of off-balance sheet commitments, including commitments to fund loans and unused lines of credit, as well as letters of credit outstanding. Deferred Federal Expense Estimated Useful Lives and Methods of Depreciation [Table Text Block] Tabular disclosure of estimated useful lives and methods of depreciation of premises and equipment. Assets measured at fair value Entity [Domain] Legal Entity [Axis] us-gaap_PreferredStockDividendRatePercentage Preferred Stock, Dividend Rate, Percentage Current Federal Expense Realized (Gains) Losses on Sale of AFS Securities Gains (Losses) on Securities Arising During the Year us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax Realized (Gains) Losses on Sale of AFS Securities us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1 Class of Warrant or Right, Exercise Price of Warrants or Rights us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights Class of Warrant or Right, Number of Securities Called by Warrants or Rights cban_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssetsRule1 Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets Rule 1 The new minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action as per Basel III framework. cban_IncreaseInTierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets Increase in Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets The increase in minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action as per Basel III framework. cban_Tier1CapitalConservationBufferOfRiskWeightedAssets Tier 1 Capital Conservation Buffer of Risk Weighted Assets Tier 1 Capital conversion buffer of risk weighted assets as per Basel III framework. Bank-Owned Life Insurance Entity Common Stock, Shares Outstanding (in shares) Numerator us-gaap_IncomeTaxesPaid Income Taxes Paid-In Capital Denominator Colony Bank [Member] Colony Bank, a subsidiary of Colony Bankcorp. us-gaap_InterestPaidNet Interest Expense Stockholders’ Equity Other Service Charges, Commissions and Fees us-gaap_AssetsFairValueDisclosureRecurring Fair Value Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Trading Symbol Standby Letters of Credit Comprehensive Income (Loss) Note [Text Block] Common Equity Tier I Risk Based Capital Required for Capital Adequacy to Risk-Weighted Assets The minimum Common Equity Tier One Capital Ratio (Common Equity Tier 1 Capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action. us-gaap_StockholdersEquity Balance Balance Intangible Assets, Finite-Lived, Policy [Policy Text Block] Schedule of Subordinated Borrowing [Table Text Block] Commitments and Contingencies us-gaap_Liabilities Subordinated Borrowings Disclosure [Text Block] US Government Agencies Debt Securities [Member] Other Liabilities Other Deposits us-gaap_DepositsFairValueDisclosure Trust Preferred Securities Subject to Mandatory Redemption [Member] Cash Flows from Operating Activities us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent Deferred Compensation Liability, Current and Noncurrent Common Equity Tier I 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. Statement [Line Items] Change in Net Unrealized Gains (Losses) on Securities Available for Sale, Net of Reclassification Adjustment and Tax Effects Change in Unrealized Gains (Losses) on Securities Available for Sale, Net of Reclassification Adjustment and Tax Effects Cash and Short-Term Investments FDIC Assessment Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] Loans, Net us-gaap_NoninterestExpense Federal Home Loan Bank Stock us-gaap_InvestmentInFederalHomeLoanBankStockFairValueDisclosure us-gaap_OtherNoninterestExpense Other Foreclosed Property Interest income recognized with no related allowance Amount of interest income (reversal), recognized on accrual basis, on financing receivables that are recognized as impaired, for which there is no related allowance for credit losses. AOCI Attributable to Parent [Member] Interest income recognized Amount of interest income (reversal) recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired. Interest income recognized with an allowance Amount of interest income (reversal), recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired. Fair Value, by Balance Sheet Grouping [Table Text Block] Property, plant and equipment, useful life (Year) Fair Value Disclosures [Text Block] Condensed Financial Information of Parent Company Only Disclosure [Text Block] Loan Origination Commitments [Member] Directors’ Fees Noninterest Expenses ASSETS Construction in Progress [Member] Furniture and Fixtures [Member] us-gaap_NetCashProvidedByUsedInFinancingActivities Commitments to Extend Credit us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent Amounts Reclassified from Accumulated Other Comprehensive Income Other Comprehensive Income Before Reclassification us-gaap_NetCashProvidedByUsedInInvestingActivities us-gaap_NetCashProvidedByUsedInOperatingActivities Increase (Decrease) in Cash Net Increase (Decrease) in Cash and Cash Equivalents Leasehold Improvements [Member] Other Comprehensive Income (Loss) Building [Member] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Axis] Land [Member] us-gaap_CashReserveDepositRequiredAndMade Cash Reserve Deposit Required and Made Property, Plant and Equipment, Policy [Policy Text Block] us-gaap_OperatingLeasesFutureMinimumPaymentsDue us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears 2021 Transfers and Servicing of Financial Assets, Transfers of Financial Assets, Policy [Policy Text Block] us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears 2019 us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears 2020 us-gaap_DebtAndCapitalLeaseObligations us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent 2018 us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour 2021 us-gaap_LongTermDebt us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree 2020 Other Borrowed Money Financial Instruments [Domain] us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock Dividends Paid on Preferred Stock us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo 2019 us-gaap_PaymentsOfDividendsCommonStock Dividends Paid on Common Stock us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths 2018 Financial Instrument [Axis] Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 3 [Member] Retained Earnings [Member] us-gaap_LineOfCredit Long-term Line of Credit Additional Paid-in Capital [Member] Fair Value Hierarchy [Domain] Proceeds from Maturities, Calls and Paydowns of Investment Securities TCJ Act Reclassification Represents the changes in stockholders' equity attributable to tax rate changes. 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Percentage of loan portfolio concentrated in loans secured by real estate. 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