Document and Entity Information [Abstract] Document Information [Table] Legal Entity [Axis] Entity [Domain] Represents the Retirement Plan Number 002. E B P 002 [Member] Bank First Retirement Plan Document Information [Line Items] Document Type Entity Registrant Name Entity Central Index Key Amendment Flag STATEMENTS OF NET ASSETS AVAILABLE FOR BENEFITS EBP, Statement of Net Asset Available for Benefit [Table] Investment Type [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] Mutual Fund [Member] Mutual Fund Mutual funds Common Collective Trust [Member] Common Trust Fund Common collective fund EBP, Pooled Separate Account [Member] Pooled Separate Fund Pooled separate funds EBP, Employer, Common Stock [Member] Common Stock Bank First Corporation common stock EBP, Statement of Net Asset Available for Benefit [Line Items] STATEMENTS OF NET ASSETS AVAILABLE FOR BENEFITS EBP, Asset [Abstract] ASSETS EBP, Investment, Fair Value [Abstract] Investments, at fair value: EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value TOTAL INVESTMENTS Total Plan's assets EBP, Investment, Contract Value [Abstract] Investments at contract value EBP, Investment, Excluding Plan Interest in Master Trust, Contract Value Fully benefit-responsive investment contract EBP, Net Asset Available for Benefit Net assets available for benefits, END OF YEAR Net assets available for benefits, BEGINNING OF YEAR Net assets available for benefits per the financial statements NET ASSETS AVAILABLE FOR BENEFITS STATEMENT OF CHANGES IN NET ASSETS AVAILABLE FOR BENEFITS EBP, Statement of Change in Net Asset Available for Benefit [Table] EBP, Statement of Change in Net Asset Available for Benefit [Line Items] STATEMENT OF CHANGES IN NET ASSETS AVAILABLE FOR BENEFITS EBP, Change in Net Asset Available for Benefit, Increase (Decrease) [Abstract] CHANGE IN NET ASSETS AVAILABLE FOR BENEFITS EBP, Change in Net Asset Available for Benefit, Increase [Abstract] ADDITIONS TO NET ASSETS ATTRIBUTED TO: EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment [Abstract] Investment income: EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Gain (Loss) on Investment Net appreciation in fair value of investments EBP, Change in Net Asset Available for Benefit, Increase from Interest and Dividend Income on Investment Interest and dividends EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Other Investment Income (Loss) Other EBP, Change in Net Asset Available for Benefit, Increase from Contribution [Abstract] Contributions: EBP, Change in Net Asset Available for Benefit, Increase from Employer Contribution, Cash and Noncash Participant EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Excluding Rollover Employer EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Rollover Rollover EBP, Change in Net Asset Available for Benefit, Increase TOTAL ADDITIONS EBP, Change in Net Asset Available for Benefit, Decrease [Abstract] DEDUCTIONS FROM NET ASSETS ATTRIBUTED TO: EBP, Change in Net Asset Available for Benefit, Decrease from Payment to Participant Benefits paid to participants EBP, Change in Net Asset Available for Benefit, Decrease from Administrative Expense Administrative expenses EBP, Change in Net Asset Available for Benefit, Decrease TOTAL DEDUCTIONS EBP, Change in Net Asset Available for Benefit, Increase (Decrease) CHANGE IN NET ASSETS AVAILABLE FOR BENEFITS Change in net assets available for benefits per the financial statements Description of Plan EBP, Description of Plan [Table] EBP, Description of Plan [Line Items] Description of Plan EBP, Description of Plan [Text Block] Description of Plan Summary of Significant Accounting Policies EBP, Accounting Policy [Table] EBP, Accounting Policy [Line Items] Summary of Significant Accounting Policies EBP, Summary of Accounting Policy [Text Block] Summary of Significant Accounting Policies Concentrations EBP, Risk and Uncertainty [Table] EBP, Risk and Uncertainty [Line Items] Concentrations EBP, Risk and Uncertainty [Text Block] Concentrations Fair Value Measurements EBP, Investment, Fair Value and NAV [Table] EBP, Investment, Fair Value and NAV [Line Items] Fair Value Measurements EBP, Investment, Fair Value and NAV [Text Block] Fair Value Measurements Tax Status EBP, Tax Status [Table] EBP, Tax Status [Line Items] Tax Status EBP, Tax Status [Text Block] Tax Status Transactions with Related Parties and Parties-in-Interest EBP, Related Party and Party-in-Interest Transactions [Table] EBP, Related Party and Party-in-Interest Transactions [Line Items] Transactions with Related Parties and Parties-in-Interest EBP, Related Party and Party-in-Interest Transactions [Text Block] Transactions with Related Parties and Parties-in-Interest Amounts Owed to Participants Withdrawing from the Plan Disclosure of information about liability of employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan Liability [Table] 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. Employee Benefit Plan Liability [Line Items] Amounts Owed to Participants Withdrawing from the Plan The entire disclosure of amount owed to participants withdrawing from the plan. Employee Benefit Plan, Amount Owed to Participants [Text Block] Amounts Owed to Participants Withdrawing from the Plan Reconciliation of Financial Statements to Form 5500 EBP, Reconciliation of Financial Statement to Form 5500 [Table] EBP, Reconciliation of Financial Statement to Form 5500 [Line Items] Reconciliation of Financial Statements to Form 5500 EBP, Reconciliation of Financial Statement to Form 5500 [Text Block] Reconciliation of Financial Statements to Form 5500 SCHEDULE OF ASSETS EBP, Schedule of Asset Held for Investment [Table] EBP, Schedule of Asset Held for Investment [Line Items] SCHEDULE OF ASSETS EBP, Schedule of Asset Held for Investment [Text Block] SCHEDULE OF ASSETS EBP, Basis of Accounting [Policy Text Block] Basis of Accounting and Presentation EBP, Risk and Uncertainty [Policy Text Block] Risks and Uncertainties Disclosure of accounting policy for income recognition and investment valuation held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan, Investment Valuation and Income Recognition [Policy Text Block] Investment Valuation and Income Recognition EBP, Use of Estimate [Policy Text Block] Use of Estimates EBP, Payment to Participant [Policy Text Block] Payment of Benefits EBP, Risk and Uncertainty [Table Text Block] Schedule of the Plan's investments that represented 10 percent or more of the Plan's net assets available for benefits EBP, Investment, Fair Value and NAV [Table Text Block] Schedule of Plan's Assets Fair Value Hierarchy EBP, Related Party and Party-in-Interest Transactions [Table Text Block] Schedule of the transactions with Bank First Corporation common stock EBP, Reconciliation of Financial Statement to Form 5500 [Table Text Block] Reconciliation of net assets available for benefits per the financial statements Represents the minimum age criteria for plan eligibility under (employee benefit plan (EBP)). Employee Benefit Plan, Minimum Age For Plan Eligibility Minimum age for Plan eligibility Represents the minimum service period for plan eligibility under (employee benefit plan (EBP)). Employee Benefit Plan, Minimum Service Period For Plan Eligibility Minimum service period for Plan eligibility EBP, Participant Contribution, Automatic, Deferral Rate Automatic deferral rate Percentage of annual increase in deferral rate in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan Participant Contribution Automatic Deferral Rate, Annual Increase Automatic yearly increases of deferral rate EBP, Participant Contribution, Pretax, Maximum Annual Compensation to Total Compensation, Percentage Maximum deferral rate EBP, Employer Contribution, Matching Percentage Discretionary match EBP, Employer Contribution, Participant Compensation Matched, Percentage Participants' eligible compensation for matching contribution EBP, Change in Net Asset Available for Benefit, Increase from Employer Contribution, Cash Matching contributions EBP, Change in Net Asset Available for Benefit, Increase from Employer Contribution, Noncash Profit-sharing contribution Represent the percentage of vesting of profit sharing contribution in case of death, disability and attainment of retirement age. Employee Benefit Plan, Profit Sharing Contribution, Vesting Percentage, Death or Retirement Age Vesting percentage Represents the period of vesting for profit sharing contribution. Employee Benefit Plan, Profit Sharing Contribution, Vesting Period Vesting period Statistical Measurement [Axis] Statistical Measurement [Domain] Maximum [Member] Maximum Participants transfers restriction period under fully benefit responsive investment contracts. Employee Benefit Plan, Fully Benefit Responsive Investment Contract, Participant Transfers Restriction Period Participant transfers restriction period Threshold balance of participant account below which amount automatically distributed as lumpsum amount immediately. Beyond threshold amount participants can choose the date of distribution in Employee benefit plan. Employee Benefit Plan, Automatic Distribution, Threshold Amount Threshold participant vested balance EBP, Forfeited Nonvested Account Forfeited nonvested accounts EBP, Forfeited Nonvested Account, Reallocated to Participant Forfeited accounts allocated to participants Represent the percentage of vesting in case of plan termination. Employee Benefit Plan, Plan Termination, Vesting Percentage Vesting percentage EBP, Risk and Uncertainty, Concentration of Investment, Benchmark Threshold Percentage Threshold Concentration percentage EBP, Risk and Uncertainty, Concentration of Investment at Fair Value to Net Assets, Amount Bank First Corporation Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value, Inputs, Level 1, Level 2, and Level 3 [Member] Fair Value Fair Value, Inputs, Level 1 [Member] Level 1 Fair Value Measured at Net Asset Value Per Share [Member] Net asset value Represents information pertains to separate funds invested in Midcap companies. Employee Benefit Plan Pooled Separate Account, Midcap [Member] Pooled Separate fund LA Capital Mgmt/Victory - Midcap Value Represents information pertains to separate funds invested in Blue Chip companies. Employee Benefit Plan Pooled Separate Account, Blue Chip [Member] Pooled Separate fund Principal Global Investors - Blue Chip Represents information pertains to separate funds invested in Small cap S&P 600 Index companies. Employee Benefit Plan Pooled Separate Account, Small Cap Index [Member] Pooled Separate fund Principal SmallCap S&P 600 Index EBP, Fair Value, Investment, NAV, Redemption, Notice Period REDEMPTION NOTICE PERIOD EBP, Tax Determination Letter, Obtained [true false] Determination letter obtained EBP, Tax Determination Letter, Date Determination letter date EBP, Tax Qualification Status [Extensible Enumeration] Tax qualification status EBP, Related Party and Party-in-Interest [Axis] EBP, Related Party and Party-in-Interest [Domain] Represents the employer of participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan Employer [Member] Bank First Corporation EBP, Investment, Purchased, Number of Shares Purchase of stock, Number of shares EBP, Investment Acquired, Excluding Plan Interest in Master Trust, Purchase Price Purchase of stock, Value of shares on transaction dates Number of shares or units of investment in-kind transfer out of the plan by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan, Investment, Number Of Shares, In-kind Transfer out of the plan In-kind transfers of stock out of Plan, Number of shares Amount of selling price for investment, excluding plan interest in master trust, in-kind transfers of stock out of the plan by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Employee Benefit Plan, Investment In-kind Transfers of Stock Out of Plan, Excluding Plan Interest In Master Trust, Value In-kind transfers of stock out of Plan, Value of shares on transaction dates EBP, Investment, Sold, Number of Shares Sales of stock, Number of shares EBP, Investment Sold, Excluding Plan Interest in Master Trust, Selling Price Sales of stock, Value of shares on transaction dates EBP, Investment, Number of Shares Number of shares held EBP, Liability to Participant Amounts owed to participants withdrawing from the plan EBP, Form 5500 Caption, Net Assets [Abstract] Reconciliation of net assets available for benefits EBP, Reconciliation to Form 5500, Net Asset Available for Benefit, Contract Value to Current Value Adjustment Common collective fund valued at net asset value per the financial statements and fair value per the Form 5500 EBP, Form 5500 Caption, Net Assets NET ASSETS AVAILABLE FOR BENEFITS PER FORM 5500 EBP, Form 5500 Caption, Net Income (Loss) [Abstract] Reconciliation of the change in net assets available for plan benefits EBP, Reconciliation to Form 5500, Change in Net Asset Available for Benefit, Increase (Decrease) from Contract Value to Current Value Change in differential between net asset value and fair value of common collective fund EBP, Form 5500 Caption, Net Income (Loss) CHANGE IN NET ASSETS AVAILABLE FOR BENEFITS PER FORM 5500 Investment, Identifier [Axis] EBP, Plan Number Plan number Entity Tax Identification Number Entity tax identification number EBP, Asset Held for Investment, Party-in-Interest [true false] EBP, Asset Held for Investment, Party-in-Interest [true false] EBP, Investment, Issuer Name [Extensible Enumeration] EBP, Investment, Issuer Name [Extensible Enumeration] EBP, Investment, Current Value, Type [Extensible Enumeration] EBP, Investment, Current Value, Type [Extensible Enumeration] EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Current Value TOTAL INVESTMENTS