Loans and Leases Receivable Disclosure [Abstract] Financing Receivable, Past Due [Table] Financing Receivable, Past Due [Table] Financing Receivable Portfolio Segment [Axis] Financing Receivable Portfolio Segment [Axis] Financing Receivable Portfolio Segment [Domain] Financing Receivable Portfolio Segment [Domain] One- to Four-Family Segment [Member] Residential Portfolio Segment [Member] Commercial Segment [Member] Commercial Portfolio Segment [Member] Consumer Segment [Member] Consumer Portfolio Segment [Member] Class of Financing Receivable [Axis] Class of Financing Receivable [Axis] Financing Receivable, Recorded Investment, Class of Financing Receivable [Domain] Class of Financing Receivable [Domain] Originated [Member] One To Four Family Loans Originated [Member] One To Four Family Loans Originated [Member] Correspondent Purchased [Member] One To Four Family Loans Correspondent Purchased [Member] Correspondent purchased loan secured by residential real estate as a single family home or a multi-unit dwelling of two to four units. Bulk Purchased [Member] One To Four Family Loans Bulk Purchased [Member] Bulk purchased loan secured by residential real estate as a single family home or a multi-unit dwelling of two to four units. Commercial Real Estate [Member] Commercial Real Estate Portfolio Segment [Member] Commercial and Industrial [Member] Commercial Loan [Member] Home Equity [Member] Home Equity Line of Credit [Member] Other [Member] Consumer Loan [Member] Financing Receivable, Past Due [Line Items] Financing Receivable, Past Due [Line Items] Financing receivable, nonaccrual loans Financing Receivable, Nonaccrual Property, Plant and Equipment [Table] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Land [Member] Land [Member] Building and Improvements [Member] Building and Building Improvements [Member] Furniture, Fixtures and Equipment [Member] Furniture and Fixtures [Member] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Property, plant and equipment, gross Property, Plant and Equipment, Gross Accumulated depreciation, property, plant and equipment Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Property, plant and equipment, net Property, Plant and Equipment, Net Employee Stock Ownership Plan (ESOP), Shares in ESOP [Abstract] Employee Benefit Plans Compensation and Employee Benefit Plans [Text Block] Fair Value Disclosures [Abstract] Schedule Of Fair Value Assets Measured On A Recurring Basis Fair Value, Assets Measured on Recurring Basis [Table Text Block] Schedule Of Carrying Amounts And Estimated Fair Values Of Financial Instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Business Combinations [Abstract] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Capital City Bancshares, Inc. [Member] Capital City Bancshares [Member] Capital City Bancshares [Member] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Regulatory and Outside Services [Member] Regulatory and Outside Services [Member] Primary financial statement caption encompassing regulatory and outside services Business Acquisition [Line Items] Business Acquisition [Line Items] Fair value of loans acquired Business Combination, Acquired Receivable, Fair Value Fair value of deposits acquired Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposits The fair value of customer deposits acquired in a business combination PCI loans, contractually required payments receivable at acquisition Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, Contractually Required Payments Receivable at Acquisition PCI loans, cash flows expected to be collected at acquisition Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, Cash Flows Expected to be Collected at Acquisition Number of common stock shares issued Business Acquisition, Equity Interest Issued or Issuable, Number of Shares Total merger consideration Business Combination, Consideration Transferred Closing stock price Business Acquisition, Share Price Merger-related expenses incurred Business Combination, Acquisition Related Costs Schedule of Impaired Financing Receivable [Table] Schedule of Impaired Financing Receivable [Table] Financing Receivable, Impaired [Line Items] Financing Receivable, Impaired [Line Items] Average Recorded Investment, No Related Allowance Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment Average Recorded Investment, Allowance Recorded Impaired Financing Receivable, with Related Allowance, Average Recorded Investment Average Recorded Investment Impaired Financing Receivable, Average Recorded Investment Interest Income Recognized, No Related Allowance Impaired Financing Receivable, with No Related Allowance, Interest Income, Accrual Method Interest Income Recognized, Allowance Recorded Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method Interest Income Recognized Impaired Financing Receivable, Interest Income, Accrual Method Marketable Securities [Abstract] Schedule of Held-to-maturity Securities [Table] Debt Securities, Held-to-maturity [Table] Financial Instrument [Axis] Financial Instrument [Axis] Financial Instruments [Domain] Financial Instruments [Domain] MBS [Member] Residential Mortgage Backed Securities [Member] GSE Debentures [Member] US Government-sponsored Enterprises Debt Securities [Member] Municipal Bonds [Member] Municipal Bonds [Member] Schedule of Held-to-maturity Securities [Line Items] Schedule of Held-to-maturity Securities [Line Items] Held-to-maturity Securities, Amortized Cost Debt Securities, Held-to-maturity Held-to-maturity Securities, Gross Unrealized Gains Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain Held-to-maturity Securities, Gross Unrealized Losses Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss Held-to-maturity securities, Estimated Fair Value Debt Securities, Held-to-maturity, Fair Value Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Line Items] Debt Securities, Available-for-sale [Line Items] Available-for-sale Securities, Amortized Cost Debt Securities, Available-for-sale, Amortized Cost Available-for-sale Securities, Gross Unrealized Gains Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax Available-for-sale Securities, Gross Unrealized Losses Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax Available-for-sale Securities, Estimated Fair Value Debt Securities, Available-for-sale Income Tax Disclosure [Abstract] Current, Federal Current Federal Tax Expense (Benefit) Current, State Current State and Local Tax Expense (Benefit) Current income tax expense Current Federal, State and Local, Tax Expense (Benefit) Deferred, Federal Deferred Federal Income Tax Expense (Benefit) Deferred, State Deferred State and Local Income Tax Expense (Benefit) Deferred income tax expense Deferred Federal, State and Local, Tax Expense (Benefit) Income tax expense Income Tax Expense (Benefit) Debt Disclosure [Abstract] Schedule of Short-term Debt [Table] Schedule of Short-term Debt [Table] Debt, Type [Axis] Short-term Debt, Type [Axis] Debt, Type [Domain] Short-term Debt, Type [Domain] FHLB Advances [Member] Federal Home Loan Bank Advances [Member] Statistical Measurement [Axis] Statistical Measurement [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] Weighted Average [Member] Weighted Average [Member] Debt [Line Items] Short-term Debt [Line Items] FHLB advances Advances from Federal Home Loan Banks Deferred prepayment penalty Prepayment Penalty On FHLB Advances Penalty paid as a result of prepaying FHLB advances. Deferred penalty is recognized in interest expense over the life of the new advances. FHLB advances, outstanding balance Long-term Federal Home Loan Bank Advances Weighted average contractual interest rate on FHLB advances Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Interest Rate at Period End Weighted average effective interest rate on FHLB advances Effective Rate FHLB Advances States the interest rate applicable to Federal Home Loan Bank advances outstanding as of the Balance Sheet date, including the net impact of interest rate swaps and the amortization of deferred prepayment penalties Financing Receivable, Troubled Debt Restructuring [Table] Financing Receivable, Troubled Debt Restructuring [Table] Financing Receivable, Troubled Debt Restructuring [Line Items] Financing Receivable, Troubled Debt Restructuring [Line Items] Number of Contracts Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts Recorded Investment Financing Receivable, Troubled Debt Restructuring, Subsequent Default Condensed Financial Information Disclosure [Abstract] Statement [Table] Statement [Table] Consolidated Entities [Axis] Consolidated Entities [Axis] Consolidated Entities [Domain] Consolidated Entities [Domain] Capitol Federal Financial Inc [Member] Parent Company [Member] Statement [Line Items] Statement [Line Items] INTEREST AND DIVIDEND INCOME: Interest and Dividend Income, Operating [Abstract] Dividend income from the Bank Dividend Income From Bank Dividend income from bank subsidiary. Interest income from other investments Other Interest and Dividend Income Total interest and dividend income Interest and Dividend Income, Operating INTEREST EXPENSE Interest Expense NET INTEREST INCOME Interest Income (Expense), Net NON-INTEREST INCOME Noninterest Income NON-INTEREST EXPENSE: Noninterest Expense [Abstract] Salaries and employee benefits Labor and Related Expense Regulatory and outside services Regulatory And Professional Fees Fees charged for services from professionals such as lawyers and accountants, and fees paid to regulators for conducting regulatory examinations. Other non-interest expense Other Noninterest Expense Total non-interest expense Noninterest Expense INCOME BEFORE INCOME TAX EXPENSE AND EQUITY IN EXCESS OF DISTRIBUTION OVER EARNINGS OF SUBSIDIARY Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest INCOME TAX EXPENSE (BENEFIT) INCOME BEFORE EQUITY IN EXCESS OF DISTRIBUTION OVER EARNINGS OF SUBSIDIARY Income Before Equity In Undistributed Overdistributed Earnings Of Subsidiary Income before equity in undistributed (overdistributed) earnings of subsidiary. EQUITY IN EXCESS OF DISTRIBUTION OVER EARNINGS OF SUBSIDIARY Equity In Excess Of Distribution Over Undistributed Earnings Of Subsidiary Equity in excess of distribution over/(undistributed) earnings of subsidiary NET INCOME Net Income (Loss) Attributable to Parent Selected Quarterly Financial Information [Abstract] Total interest and dividend income Net interest and dividend income Provision for credit losses Provision for Loan and Lease Losses Net income Basic EPS Earnings Per Share, Basic Diluted EPS Earnings Per Share, Diluted Dividends declared per share Common Stock, Dividends, Per Share, Declared Average number of basic shares outstanding Weighted Average Number of Shares Outstanding, Basic Average number of diluted shares outstanding Weighted Average Number of Shares Outstanding, Diluted CASH FLOWS FROM OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] Net income Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Equity in excess of distribution over earnings of subsidiary Depreciation of equipment Depreciation, Nonproduction Loss on disposal of premises and equipment Gain (Loss) on Disposition of Property Plant Equipment Provision for deferred income taxes Deferred Income Tax Expense (Benefit) Changes in: Increase (Decrease) in Operating Capital [Abstract] Other assets Increase (Decrease) in Other Operating Assets Income taxes receivable/payable Increase Decrease Income Taxes The net change during a reporting period of income taxes payable/receivable and deferred income tax assets/liabilities. Accounts payable and accrued expenses Increase (Decrease) in Accounts Payable and Accrued Liabilities Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities CASH FLOWS FROM INVESTING ACTIVITIES: Net Cash Provided by (Used in) Investing Activities [Abstract] Principal collected on note receivable from ESOP Proceeds from Collection of Notes Receivable Cash acquired from acquisition Cash Acquired from Acquisition Purchase of equipment Payments to Acquire Property, Plant, and Equipment Proceeds from the redemption of common equity securities related to the redemption of junior subordinated debentures Proceeds from Sale of Other Investments Net cash provided by (used in) investing activities Net Cash Provided by (Used in) Investing Activities CASH FLOWS FROM FINANCING ACTIVITIES: Net Cash Provided by (Used in) Financing Activities [Abstract] Net payment from subsidiary related to restricted stock awards Proceeds, Issuance of Shares, Share-based Payment Arrangement, Excluding Option Exercised Cash dividends paid Payments of Dividends Repayment of other borrowings Repayments of Subordinated Debt Stock options exercised Proceeds from Stock Options Exercised Net cash used in financing activities Net Cash Provided by (Used in) Financing Activities NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS Cash and Cash Equivalents, Period Increase (Decrease) CASH AND CASH EQUIVALENTS: Cash and Cash Equivalents, at Carrying Value [Abstract] Beginning of year Cash and Cash Equivalents, at Carrying Value End of year SUPPLEMENTAL DISCLOSURE OF NONCASH INVESTING AND FINANCING ACTIVITIES: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Common stock issued for acquisition Stock Issued Capital contribution to subsidiary in conjunction with acquisition of CCB Capital Contributions To Subsidiaries The fair value of capital contributions to subsidiaries during the period in noncash transactions ASSETS: Assets [Abstract] Cash and cash equivalents Investment in the Bank Investment In Bank And Parent Company Parent company investment in bank subsidiary. Note receivable - ESOP E S O P Note Receivable ESOP note receivable. Other assets Other Assets Income taxes receivable, net Income Taxes Receivable TOTAL ASSETS Assets LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities and Equity [Abstract] LIABILITIES: Liabilities [Abstract] Junior subordinated debentures Debt Instrument, Face Amount Accounts payable and accrued expenses Accounts Payable and Other Accrued Liabilities Total liabilities Liabilities STOCKHOLDERS' EQUITY: Stockholders' Equity Attributable to Parent [Abstract] Preferred stock, $.01 par value; 100,000,000 shares authorized, no shares issued or outstanding Preferred Stock, Value, Issued Common stock, $.01 par value; 1,400,000,000 shares authorized; 141,440,030 and 141,225,516 shares issued and outstanding as of September 30, 2019 and 2018, respectively Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital, Common Stock Unearned compensation - ESOP Unearned ESOP Shares Retained earnings Retained Earnings (Accumulated Deficit) AOCI, net of tax Accumulated Other Comprehensive Income (Loss), Net of Tax Total stockholders' equity Stockholders' Equity Attributable to Parent TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities and Equity Preferred stock, par value Preferred Stock, Par or Stated Value Per Share Preferred stock, shares authorized Preferred Stock, Shares Authorized Preferred stock, shares issued Preferred Stock, Shares Issued Preferred stock, shares outstanding Preferred Stock, Shares Outstanding Common stock, par value Common Stock, Par or Stated Value Per Share Common stock, shares authorized Common Stock, Shares Authorized Common stock, shares issued Common Stock, Shares, Issued Common stock, shares outstanding Common Stock, Shares, Outstanding Banking and Thrift [Abstract] Liquidation account balance Liquidation Account The amount equal to the former mutual holding company's ownership interest in the retained earnings of the former company, as determined as of a specific date, for the benefit of certain depositors of the Bank. Capital Conservation Buffer, Annual Increase Capital Conservation Buffer, Annual Increase Amount of annual percentage increase in required capital conservation buffer above minimum risk-based capital ratios Required Capital Conservation Buffer Required Capital Conservation Buffer Amount of required capital conservation buffer above minimum risk-based capital ratios Property, Plant and Equipment, Net [Abstract] Premises And Equipment, Net Property, Plant and Equipment Disclosure [Text Block] Accounting Policies [Abstract] Summary Of Significant Accounting Policies [Table] Summary Of Significant Accounting Policies [Table] Summary Of Significant Accounting Policies [Table] Traditional Banking Offices [Member] Traditional Banking Offices [Member] Traditional Banking Offices [Member] In-Store Banking Offices [Member] In Store Banking Offices [Member] In-Store Banking Offices [Member] Scenario [Axis] Scenario [Axis] Scenario [Domain] Scenario [Domain] Forecast [Member] Forecast [Member] Summary Of Significant Accounting Policies [Line Items] Summary Of Significant Accounting Policies [Line Items] Summary Of Significant Accounting Policies [Line Items] Number of Stores Number of Stores Restricted cash and cash equivalents Restricted Cash and Cash Equivalents Restricted cash and cash equivalents, balance sheet location Restricted Cash and Cash Equivalents, Asset, Statement of Financial Position [Extensible List] Interest-bearing deposits held at the Federal Reserve Bank Interest Bearing Deposits Held At Federal Reserve Bank Interest Bearing Deposits Held At Federal Reserve Bank Average daily balance of required reserves at the Federal Reserve Bank Average Daily Required Reserve Balance At Federal Reserve Bank Average Daily Required Reserve Balance At Federal Reserve Bank Other intangible assets, estimated life Acquired Finite-lived Intangible Assets, Weighted Average Useful Life Cumulative effect of adopting ASU 2014-09 Cumulative Effect on Retained Earnings, Net of Tax Operating Lease, Right-of-Use Asset Operating Lease, Right-of-Use Asset Operating Lease, Liability Operating Lease, Liability Transfer of HTM securities, at amortized cost, to AFS securities Debt Securities, Held-to-maturity, Transfer, Amount Summary Of Shares Held In The ESOP Trust Employee Stock Ownership Plan (ESOP) Disclosures [Table Text Block] Loans Receivable And Allowance For Credit Losses Financing Receivables [Text Block] 2020 Operating Leases, Future Minimum Payments Due, Next Twelve Months 2021 Operating Leases, Future Minimum Payments, Due in Two Years 2022 Operating Leases, Future Minimum Payments, Due in Three Years 2023 Operating Leases, Future Minimum Payments, Due in Four Years 2024 Operating Leases, Future Minimum Payments, Due in Five Years Thereafter Operating Leases, Future Minimum Payments, Due Thereafter Future minimum rental commitments, total Operating Leases, Future Minimum Payments Due Public unit deposits Pledged Financial Instruments, Not Separately Reported, Securities for Public Unit Deposits The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for public unit deposits, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party. Repurchase agreements Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements FRB of Kansas City Pledged Financial Instruments, Not Separately Reported, Securities for Other Debt Facilities Total securities pledged as collateral Pledged Financial Instruments, Not Separately Reported, Securities Federal income tax expense computed at statutory Federal rate, Amount Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount Federal income tax expense computed at statutory Federal rate, Percentage Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Increases (Decreases) In Taxes Resulting From: Increases (Decreases) In Taxes Abstract Increases (Decreases) in taxes resulting from: State taxes, net of Federal tax effect, Amount Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount State taxes, net of Federal tax effect, Percentage Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent Deferred tax liability remeasurement, net, Amount Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act, Amount Deferred tax liability remeasurement, net, Percentage Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act, Percent Low income housing tax credits, net, Amount Effective Income Tax Rate Reconciliation, Tax Credit, Amount Low income housing tax credits, net, Percentage Effective Income Tax Rate Reconciliation, Tax Credit, Percent ESOP related expenses, net, Amount ESOP Related Expenses Net ESOP related expenses, net. ESOP related expenses, net, Percentage Effective Income Tax Rate ESOP Related Expenses Net Effective income tax rate ESOP related expenses, net. Other, Amount Effective Income Tax Rate Reconciliation, Other Adjustments, Amount Other, Percentage Effective Income Tax Rate Reconciliation, Other Adjustments, Percent Income tax expense, Percentage Effective Income Tax Rate Reconciliation, Percent Earnings Per Share [Abstract] Earnings Per Share Earnings Per Share [Text Block] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value, Disclosure Item Amounts [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Carrying Amount [Member] Reported Value Measurement [Member] Estimated Fair Value [Member] Estimate of Fair Value Measurement [Member] Fair Value, Hierarchy [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy and NAV [Domain] Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] Fair Value, Inputs, Level 1 [Member] Significant Other Observable Inputs (Level 2) [Member] Fair Value, Inputs, Level 2 [Member] Significant Unobservable Inputs (Level 3) [Member] Fair Value, Inputs, Level 3 [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Assets: Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract] Cash and cash equivalents Cash and Cash Equivalents, Fair Value Disclosure AFS securities HTM securities Loans receivable Loans Receivable, Fair Value Disclosure FHLB stock Investment in Federal Home Loan Bank Stock, Fair Value Disclosure Interest rate swaps Derivative Asset Liabilities: Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] Deposits Deposits, Fair Value Disclosure FHLB borrowings Federal Home Loan Bank Borrowings, Fair Value Disclosure Other borrowings Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure Interest rate swaps Derivative Liability Goodwill and Intangible Assets Disclosure [Abstract] Intangible Assets Goodwill and Intangible Assets Disclosure [Text Block] Regulatory Capital Requirements Regulatory Capital Requirements under Banking Regulations [Text Block] Schedule of Goodwill and Intangible Assets Schedule of Intangible Assets and Goodwill [Table Text Block] Schedule of Core Deposit and Other Intangible Assets, Future Amortization Expense Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Other than temporary impairments, amount Other than Temporary Impairment Losses, Investments Trust Preferred Securities [Member] Trust Preferred Securities [Member] A collateralized debt obligation backed by a shared pool of trust preferred securities. Issuers include companies in highly regulated industries such as banks, insurance companies and regulated utilities as well as some general corporate issuers. Most are rated by one or more of the standard rating agencies. Proceeds received from sale of AFS securities Proceeds from Sale of Debt Securities, Available-for-sale Gain on sale of AFS securities Debt Securities, Available-for-sale, Realized Gain Income Statement [Abstract] Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] Deposit Account [Member] Deposit Account [Member] Loans receivable Interest and Fee Income, Loans and Leases Mortgage-backed securities (MBS) Interest Income, Securities, Mortgage Backed FHLB stock Dividend Income, Operating Investment securities Interest Income, Debt Securities, Operating Cash and cash equivalents Interest Income, Deposits with Financial Institutions INTEREST EXPENSE: Interest Expense [Abstract] Deposits Interest Expense, Deposits FHLB borrowings Interest Expense, Federal Home Loan Bank and Federal Reserve Bank Advances, Long-term Other borrowings Interest Expense, Securities Sold under Agreements to Repurchase Total interest expense PROVISION FOR CREDIT LOSSES NET INTEREST INCOME AFTER PROVISION FOR CREDIT LOSSES Interest Income (Expense), after Provision for Loan Loss NON-INTEREST INCOME: Noninterest Income [Abstract] Deposit service fees Revenue from Contract with Customer, Excluding Assessed Tax Deposit service fees, type of revenue Revenue, Product and Service [Extensible List] Income from bank-owned life insurance (BOLI) Bank Owned Life Insurance Income Other non-interest income Noninterest Income, Other Total non-interest income Information technology and related expense Communications and Information Technology Occupancy, net Occupancy, Net Advertising and promotional Advertising Expense Deposit and loan transaction costs Deposit And Loan Transaction Costs Expense paid for miscellaneous loan fees that are not deferred, and fees related to deposit transactions, such as debit card processing, electronic banking, and ATM networks. Office supplies and related expense Supplies and Postage Expense Federal insurance premium Federal Deposit Insurance Corporation Premium Expense Other non-interest expense INCOME BEFORE INCOME TAX EXPENSE INCOME TAX EXPENSE Basic earnings per share (EPS) Diluted EPS Federal corporate income tax rate Revaluation of net deferred tax liability Tax Cuts and Jobs Act, Change in Tax Rate, Deferred Tax Liability, Income Tax Benefit Effective income tax rate Valuation allowance Deferred Tax Assets, Valuation Allowance Unrecognized tax benefits Unrecognized Tax Benefits Open tax year Open Tax Year Schedule Of Balance Sheets Condensed Balance Sheet [Table Text Block] Schedule Of Statements Of Income Condensed Income Statement [Table Text Block] Schedule Of Statements Of Cash Flows Condensed Cash Flow Statement [Table Text Block] Financing Receivable, Credit Quality Indicator [Table] Financing Receivable, Credit Quality Indicator [Table] Internal Credit Assessment [Axis] Internal Credit Assessment [Axis] Financing Receivable, by Credit Quality Indicator [Domain] Internal Credit Assessment [Domain] Special Mention [Member] Special Mention [Member] Substandard [Member] Substandard [Member] Financing Receivable, Credit Quality Indicator [Line Items] Financing Receivable, Credit Quality Indicator [Line Items] Financing receivable, total recorded investment Loans and Leases Receivable, Net of Deferred Income Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Class of Financing Receivable [Domain] Construction [Member] Construction Loans [Member] Loans Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Loans receivable, gross Loans and Leases Receivable, before Fees, Gross ACL Loans and Leases Receivable, Allowance Discounts/unearned loan fees Loans and Leases Receivable, Deferred Income Premiums/deferred costs Loans And Leases Receivable Premiums Deferred Costs Amount of deferred premiums over face amounts of purchased and acquired loans and unamortized costs incurred to originate loans. Loans receivable, net Loans and Leases Receivable, Net Amount Amortized Cost, Estimated Fair Value, and Gross Unrealized Gains and Losses Of AFS Securities Debt Securities, Available-for-sale [Table Text Block] Amortized Cost, Estimated Fair Value, and Gross Unrealized Gains and Losses Of HTM Securities Debt Securities, Held-to-maturity [Table Text Block] Schedule Of Estimated Fair Value And Gross Unrealized Losses Of Securities In Continuous Unrealized Loss Position Unrealized Gain (Loss) on Investments [Table Text Block] Schedule Of Contractual Maturities Investments Classified by Contractual Maturity Date [Table Text Block] Schedule Of Taxable And Non-taxable Components Of Interest Income Interest Income and Interest Expense Disclosure [Table Text Block] Schedule Of Carrying Value Of Securities Pledged As Collateral Schedule Of Carrying Value Of Securities Pledged As Collateral Table Text Block Schedule Of Carrying Value Of Securities Pledged As Collateral. Share-based Payment Arrangement, Noncash Expense [Abstract] Stock-Based Compensation Share-based Payment Arrangement [Text Block] Revenue from Contract with Customer [Abstract] Revenue Recognition Revenue from Contract with Customer [Text Block] Summary of Loans Receivable Summary Of Loans Receivable By Category [Table Text Block] Tabular disclosure of the various types of loans receivable and for each the gross carrying value as of the balance sheet date. Recorded Investment in Loans, Past Due Financing Receivable, Past Due [Table Text Block] Recorded Investment in Loans, Nonaccrual Financing Receivable, Nonaccrual [Table Text Block] Recorded Investment in Classified Loans Financing Receivable Credit Quality Indicators [Table Text Block] Weighted Average Loan-to-Value and Credit Score Information Financing Receivable Credit Quality Indicator Loan To Value And Credit Scores [Table Text Block] Financing Receivable Credit Quality Indicator Loan To Value And Credit Scores Troubled Debt Restructurings on Financing Receivables Financing Receivable, Troubled Debt Restructuring [Table Text Block] Impaired Loans by Class Impaired Financing Receivables [Table Text Block] Allowance for Credit Losses Financing Receivable, Allowance for Credit Loss [Table Text Block] Number of Contracts Financing Receivable, Modifications, Number of Contracts Pre-Restructured Outstanding Financing Receivable, Troubled Debt Restructuring, Premodification Post-Restructured Outstanding Financing Receivable, Troubled Debt Restructuring, Postmodification Deferred income tax assets: Components of Deferred Tax Assets [Abstract] Unrealized loss on interest rate swaps Deferred Tax Assets, Derivative Instruments Salaries, deferred compensation and employee benefits Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Benefits ESOP compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Postretirement Benefits Net purchase discounts related to acquired loans Deferred Tax Assets, Deferred Income Low income housing partnerships Deferred Tax Assets, Investments Unrealized loss on AFS securities Deferred Tax Assets, Unrealized Losses on Available-for-Sale Securities, Gross Other Deferred Tax Assets, Other Gross deferred income tax assets Deferred Tax Assets, Gross Valuation allowance Gross deferred income tax asset, net of valuation allowance Deferred Tax Assets, Net of Valuation Allowance Deferred income tax liabilities: Components of Deferred Tax Liabilities [Abstract] FHLB stock dividends Deferred Tax Liabilities Federal Home Loan Bank Stock Dividends Deferred income tax liabilities relating to FHLB stock dividends. Premises and equipment Deferred Tax Liabilities, Property, Plant and Equipment Unrealized gain on AFS securities Deferred Tax Liabilities, Unrealized Gains On Available-for-Sale Securities Amount of deferred tax liability attributable to taxable temporary differences from unrealized gains on available-for-sale securities. Deposit intangible Deferred Tax Liabilities, Intangible Assets ACL Deferred Tax Liabilities, Allowance For Credit Losses Amount of deferred tax liability attributable to allowance for credit losses Unrealized gain on interest rate swaps Deferred Tax Liabilities, Derivatives Other Deferred Tax Liabilities, Other Gross deferred income tax liabilities Deferred Tax Liabilities, Gross Net deferred tax liabilities Deferred Tax Liabilities, Net Securities Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Statement of Stockholders' Equity [Abstract] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Common Stock [Member] Common Stock [Member] Additional Paid-In Capital [Member] Additional Paid-in Capital [Member] Unearned Compensation ESOP [Member] Employee Stock Ownership Plan [Member] A plan where shares of company stock are allocated to qualified employees based on the proportion of their qualifying compensation to total qualifying compensation. Funds are borrowed by the ESOP from the Company to purchase the Company's common stock and repaid from the Bank's contributions and dividends paid on unallocated ESOP shares. The shares pledged as collateral are reported as a reduction of stockholders' equity at cost. As ESOP shares are committed to be released from collateral each quarter, the Company records compensation expense based on the average market price of the Company's stock during the quarter. Additionally, the shares become outstanding for earnings per share ("EPS") computations once they are committed to be released. Retained Earnings [Member] Retained Earnings [Member] AOCI [Member] AOCI Attributable to Parent [Member] Balance Other comprehensive income (loss), net of tax Other Comprehensive Income (Loss), Net of Tax Reclassification of certain tax effects related to adoption of Accounting Standards Update (ASU) 2018-02 Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect Cumulative effect of ASU adoption Capital City Bancshares, Inc. (CCB) acquisition Stock Issued During Period, Value, Acquisitions ESOP activity Stock Issued During Period, Value, Employee Stock Ownership Plan Restricted stock activity, net Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures Stock-based compensation APIC, Share-based Payment Arrangement, Increase for Cost Recognition Stock options exercised Stock Issued During Period, Value, Stock Options Exercised Cash dividends to stockholders Dividends, Cash Balance Cash dividends to stockholders 2020 Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months 2021 Finite-Lived Intangible Assets, Amortization Expense, Year Two 2022 Finite-Lived Intangible Assets, Amortization Expense, Year Three 2023 Finite-Lived Intangible Assets, Amortization Expense, Year Four 2024 Finite-Lived Intangible Assets, Amortization Expense, Year Five Parent Company Financial Information (Parent Company Only) Condensed Financial Information of Parent Company Only Disclosure [Text Block] Financial Asset, Period Past Due [Axis] Financial Asset, Period Past Due [Axis] Financial Asset, Period Past Due [Domain] Financial Asset, Period Past Due [Domain] Financial Asset, 30 to 89 Days Past Due [Member] Financing Receivables, 30 to 89 Days Past Due [Member] Financing receivables that are more than 29 days past due but fewer than 90 days past due. Financial Asset, Equal to or Greater than 90 Days Past Due [Member] Financial Asset, Equal to or Greater than 90 Days Past Due [Member] Financing receivable, total delinquent loans Financing Receivable, Past Due Financing receivable, current loans Financing Receivable, Not Past Due Financing receivable, total recorded investment Summary Of The Carrying Value Of Banking Premises And Equipment Property, Plant and Equipment [Table Text Block] Schedule Of Future Minimum Rental Commitments Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Deposits and Borrowed Funds [Abstract] Deposits and Borrowed Funds [Abstract] Deposits and Borrowed Funds Debt Disclosure [Text Block] Statement of Comprehensive Income [Abstract] Other comprehensive income (loss), net of tax: Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Unrealized gains (losses) on AFS securities arising during the period, net of taxes of $(3,468), $2,499, and $1,595 Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax Unrealized gains on securities reclassified from HTM to AFS during the period, net of taxes of $(750), $0, and $0 Other Comprehensive Income (Loss), Transfers from Held-to-maturity to Available-for-Sale Securities, Net of Tax Changes in unrealized gains (losses) on cash flow hedges, net of taxes of $10,394, $(2,785), and $226 Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Parent Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Investment Holdings [Table] Investment Holdings [Table] Debt Securities [Member] Debt Securities [Member] Investment Holdings [Line Items] Investment Holdings [Line Items] Available-for-sale Securities, One year or less, Amortized Cost Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost Available-for-sale Securities, One year through five years, Amortized Cost Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Amortized Cost Available-for-sale Securities, One year or less, Estimated Fair Value Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value Available-for-sale Securities, One year through five years, Estimated Fair Value Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Fair Value Available-for-sale Securities, Estimated Fair Value Cover page. Document Type Document Type Annual Report indicator Document Annual Report Period End Date Document Period End Date Transition Report indicator Document Transition Report Commission file number Entity File Number Registrant Name Entity Registrant Name State of incorporation Entity Incorporation, State or Country Code IRS identification number Entity Tax Identification Number Address of principal executive offices location Entity Address, Address Line One City of principal executive offices location Entity Address, City or Town State of principal executive offices location Entity Address, State or Province Zip code of principal executive offices location Entity Address, Postal Zip Code Telephone number - Area code City Area Code Telephone number Local Phone Number Title of security class Title of 12(b) Security Trading symbol Trading Symbol Name of exchange on which securities are registered Security Exchange Name Well-known Seasoned Issuer indicator Entity Well-known Seasoned Issuer Voluntary Filer indicator Entity Voluntary Filers Entity current reporting status indicator Entity Current Reporting Status Interactive data current reporting status indicator Entity Interactive Data Current Filer category Entity Filer Category Smaller Reporting Company indicator Entity Small Business Emerging Growth Company indicator Entity Emerging Growth Company Shell company indicator Entity Shell Company Entity Public Float Entity Public Float Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Documents Incorporated by Reference [Text Block] Documents Incorporated by Reference [Text Block] Entity Central Index Key Entity Central Index Key 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 Amendment Flag Amendment Flag Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Measurement Frequency [Axis] Measurement Frequency [Axis] Measurement Frequency [Domain] Measurement Frequency [Domain] Fair Value, Nonrecurring [Member] Fair Value, Nonrecurring [Member] Measurement Input Type [Axis] Measurement Input Type [Axis] Measurement Input Type [Domain] Measurement Input Type [Domain] Estimated Selling Costs [Member] Measurement Input, Cost to Sell [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Loans individually evaluated for impairment Loans receivable, measurement input Loans Receivable, Measurement Input Value of input used by financial institution to measure loans receivable at fair value OREO Other Real Estate OREO, measurement input Other Real Estate Owned, Measurement Input ACL maintained for loans individually evaluated for impairment Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment Rental expense Operating Leases, Rent Expense, Net Goodwill recognized upon acquisition of CCB Goodwill, Acquired During Period Other intangible assets recognized upon acquisition of CCB Finite-lived Intangible Assets Acquired Goodwill, impairment recorded Goodwill, Impaired, Accumulated Impairment Loss Statement of Financial Position [Abstract] Cash and cash equivalents (includes interest-earning deposits of $198,809 and $122,733) Securities: Available-for-sale (AFS), at estimated fair value (amortized cost of $1,191,455 and $718,564) Held-to-maturity (HTM), at amortized cost (estimated fair value of $0 and $601,071) Loans receivable, net (allowance for credit losses (ACL) of $9,226 and $8,463) Federal Home Loan Bank Topeka (FHLB) stock, at cost Federal Home Loan Bank Stock Premises and equipment, net Deposits Deposits, Domestic FHLB borrowings Other borrowings Securities Sold under Agreements to Repurchase Advance payments by borrowers for taxes and insurance Advance Payments by Borrowers for Taxes and Insurance Deferred income tax liabilities, net Unearned compensation, Employee Stock Ownership Plan (ESOP) Accumulated other comprehensive (loss) income (AOCI), net of tax Fair Value, Recurring [Member] Fair Value, Recurring [Member] Assets Assets, Fair Value Disclosure Commitments and Contingencies Disclosure [Abstract] Unadvanced lines of credit Unadvanced Lines Of Credit Unadvanced Lines Of Credit Standby letters of credit outstanding Letters of Credit Outstanding, Amount Investments in Affordable Housing Projects [Abstract] Investment In affordable housing limited partnerships Investment In Affordable Housing Limited Partnerships The Bank's investment in low income housing partnerships Obligations related to investments in affordable housing limited partnerships Qualified Affordable Housing Project Investments, Commitment Affordable housing tax credits commitment, year to be paid Affordable Housing Tax Credits Commitment, Year to be Paid Proportional amortization expense, amount Amortization Method Qualified Affordable Housing Project Investments, Amortization Affordable housing tax credits, amount Affordable Housing Tax Credits and Other Tax Benefits, Amount Net income tax benefit, low income housing partnerships Net Income Tax Benefit, Low Income Housing Partnerships Amount of net income tax benefit recognized related to low income housing partnerships Impairment losses from the forfeiture or ineligibility of tax credits or other circumstances, amount Affordable Housing Project Investment, Write-down, Amount Doubtful [Member] Doubtful [Member] PCI Loans [Member] Purchased Credit Impaired Loans [Member] Purchased Credit Impaired Loans [Member] Non-PCI Loans [Member] Non-Purchased Credit Impaired Loans [Member] Non-Purchased Credit Impaired Loans [Member] PCI Loans Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Outstanding Balance Outstanding discounts Serviced loans for others, aggregate amount Aggregate amount of loans serviced for others Aggregate amount of loans serviced by the Bank for others. Escrow balances on loans serviced for others escrow balances held on loans serviced for others Escrow balances held by the Bank on loans serviced for others. Loan-to-value ratio securing commercial real estate loans, maximum Loan To Value Ratio For Securing Commercial Real Estate Loans Maximum Loan To Value Ratio For Securing Commercial Real Estate Loans Maximum Debt service coverage ratio for commercial real estate loans, minimum Debt Service Coverage Ratio For Commercial Real Estate Loans Minimum For commercial real estate loans, the minimum acceptable debt service coverage ratio. Loan-to-value ratio securing commercial construction loans, maximum Loan to Value Ratio for Securing Commercial Construction Loans Maximum For commercial construction loans, the maximum acceptable loan to value ratio Recorded investment of loans in process of foreclosure Mortgage Loans in Process of Foreclosure, Amount Carrying value of residential OREO Real Estate Acquired Through Foreclosure Loans receivable ACL maintained for impaired loans Impaired Financing Receivable, Related Allowance Description of Business Nature of Operations [Text Block] Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Net Presentation of Cash Flows Related to Borrowings Net Presentation of Cash Flows Related to Borrowings [Policy Text Block] Disclosure of accounting policy for net presentation of cash flows related to borrowings Securities Investment, Policy [Policy Text Block] Loans Receivable Financing Receivable, Held-for-investment [Policy Text Block] Allowance for Credit Losses Loans and Leases Receivable, Allowance for Loan Losses Policy [Policy Text Block] Federal Home Loan Bank Stock Federal Home Loan Bank Stock [Policy Text Block] Federal Home Loan Bank Stock [Policy Text Block] Premises and Equipment Property, Plant and Equipment, Policy [Policy Text Block] Other Assets Goodwill and Intangible Assets, Policy [Policy Text Block] Income Taxes Income Tax, Policy [Policy Text Block] Employee Stock Ownership Plan Employee Stock Ownership Plan (ESOP), Policy [Policy Text Block] Stock-based Compensation Share-based Payment Arrangement [Policy Text Block] Borrowed Funds Borrowed Funds [Policy Text Block] Borrowed Funds [Policy Text Block] Segment Information Segment Reporting, Policy [Policy Text Block] Low Income Housing Partnerships Low Income Housing Partnerships, Policy [Policy Text Block] Disclosure of accounting policy for low income housing partnerships Earnings Per Share Earnings Per Share, Policy [Policy Text Block] Trust Asset Management Trust Asset Management [Policy Text Block] The accounting policy for treatment of trust assets Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Interest-earning deposits Interest-bearing Deposits in Banks and Other Financial Institutions Available-for-sale securities, amortized cost Held-to-maturity securities, estimated fair value Loans receivable, allowance for credit losses FHLB Advances Due in 2020 Federal Home Loan Bank, Advances, Maturities Summary, Due in Next Twelve Months FHLB Advances Due in 2021 Federal Home Loan Bank, Advances, Maturities Summary, Due in Year Two FHLB Advances Due in 2022 Federal Home Loan Bank, Advances, Maturities Summary, Due in Year Three FHLB Advances Due in 2023 Federal Home Loan Bank, Advances, Maturities Summary, Due in Year Four FHLB Advances Due in 2024 Federal Home Loan Bank, Advances, Maturities Summary, Due in Year Five FHLB Advances Due Thereafter Federal Home Loan Bank, Advances, Maturities Summary, Due after Year Five FHLB Advances Amount Repurchase Agreements Due in 2020 Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months Repurchase Agreements Due in 2021 Long-term Debt, Maturities, Repayments of Principal in Year Two Repurchase Agreements Due in 2022 Long-term Debt, Maturities, Repayments of Principal in Year Three Repurchase Agreements Due in 2023 Long-term Debt, Maturities, Repayments of Principal in Year Four Repurchase Agreements Due in 2024 Long-term Debt, Maturities, Repayments of Principal in Year Five Repurchase Agreements Due Thereafter Long-term Debt, Maturities, Repayments of Principal after Year Five Repurchase Agreements Amount Secured Debt, Repurchase Agreements Certificates of Deposit Due in 2020 Time Deposit Maturities, Next Twelve Months Certificates of Deposit Due in 2021 Time Deposit Maturities, Year Two Certificates of Deposit Due in 2022 Time Deposit Maturities, Year Three Certificates of Deposit Due in 2023 Time Deposit Maturities, Year Four Certificates of Deposit Due in 2024 Time Deposit Maturities, Year Five Certificates of Deposit Due Thereafter Time Deposit Maturities, after Year Five Certificates of Deposit Amount Interest-bearing Domestic Deposit, Certificates of Deposits Recorded investment in loans collectively evaluated for impairment Financing Receivable, Collectively Evaluated for Impairment Recorded investment in loans individually evaluated for impairment Financing Receivable Individually Evaluated for Impairment, Recorded Investment The balance of financing receivables that were individually evaluated for impairment. ACL for loans collectively evaluated for impairment Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment Originate fixed-rate Loans and Leases Receivable, Commitments, Fixed Rates Originate adjustable-rate Loans and Leases Receivable, Commitments, Variable Rates Purchase/participate fixed-rate Commitments Outstanding To Purchase Fixed Rate Commitment to purchase/participate fixed-rate loans. Purchase/participate adjustable-rate Commitments Outstanding To Purchase Adjustable Rate Commitments to purchase/participate adjustable rate loans. Commitments outstanding to originate, purchase, or participate in loans Commitments Outstanding To Originate And Purchase Loans Commitments outstanding to originate and purchase loans. Equity [Abstract] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Other Comprehensive Income Components [Axis] Other Comprehensive Income Location [Axis] Other Comprehensive Income Components [Domain] Other Comprehensive Income Location [Domain] Unrealized Gains (Losses) on AFS Securities [Member] AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member] Unrealized Gains (Losses) on Cash Flow Hedges [Member] Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Beginning Balance Transfer of HTM securities to AFS securities Other comprehensive income (loss), before reclassifications OCI, before Reclassifications, Net of Tax, Attributable to Parent Amount reclassified from AOCI Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent Other comprehensive income (loss) Reclassification of certain income tax effects related to adoption of ASU 2018-02 Ending Balance Income Taxes Income Tax Disclosure [Text Block] Fair Value Of Financial Instruments Fair Value Disclosures [Text Block] Accumulated Other Comprehensive Income Comprehensive Income (Loss) Note [Text Block] Revenue from contracts with customers Interchange network charges Interchange Network Charges Transaction related costs paid in order to participate in debit card payment networks Low Income Housing Partnerships Affordable Housing Program [Text Block] Summary Of Capital And Total Risk-Based Capital Ratios Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table Text Block] Schedule Of Income Tax Expense Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Differences Between Effective Rates And Statutory Federal Income Tax Rate Computed On Income Before Income Tax Expense Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Deferred Income Tax Expense (Benefit) Results From Temporary Differences In Recognition Of Revenue And Expenses For Tax Summary of Deferred Tax Liability Not Recognized [Table Text Block] Components Of Net Deferred Income Tax Liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Commitments Outstanding To Originate, Purchase, Or Participate In Loans Commitments Outstanding To Originate And Purchase Loans [Table Text Block] Commitments Outstanding To Originate And Purchase Loans [Table Text Block] Schedule of Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Earnings Per Share Reconciliation Effect On Basic Earnings Per Share [Axis] Earnings Per Share Reconciliation Effect On Basic Earnings Per Share [Axis] Earnings Per Share Reconciliation, Effect On Basic Earnings Per Share [Axis] Earnings Per Share Reconciliation Effect On Basic Earnings Per Share [Domain] Earnings Per Share Reconciliation Effect On Basic Earnings Per Share [Domain] Earnings Per Share Reconciliation Effect On Basic Earnings Per Share [Domain] Average Common Shares Outstanding [Member] Average Common Shares Outstanding [Member] Average common shares outstanding Average Committed ESOP Shares Outstanding [Member] Average Committed Employee Stock Ownership Plan Shares Outstanding [Member] Average committed employee stock ownership plan shares outstanding Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Earnings Per Share Earnings Per Share Reconciliation [Abstract] Income allocated to participating securities Undistributed Earnings (Loss) Allocated to Participating Securities, Basic Net income available to common stockholders Net Income (Loss) Available to Common Stockholders, Basic Total basic average common shares outstanding Effect of dilutive stock options Weighted Average Number Diluted Shares Outstanding Adjustment Total diluted average common shares outstanding Net EPS: Earnings Per Share, Basic and Diluted [Abstract] Basic Diluted Antidilutive stock options, excluded from the diluted average common shares outstanding calculation Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Award Type [Axis] Award Type [Axis] Share-based Compensation Arrangements by Share-based Payment Award, Award Type and Plan Name [Domain] Award Type [Domain] Stock Option Plans [Member] Share-based Payment Arrangement [Member] Restricted Stock Plans [Member] Restricted Stock [Member] Incentive Stock Options [Member] Incentive Stock Options [Member] Incentive Stock Options [Member] Nonqualified Stock Options [Member] Nonqualified Stock Options [Member] Nonqualified Stock Options [Member] Minimum [Member] Minimum [Member] Maximum [Member] Maximum [Member] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] 2000 Stock Option Plan [Member] Two Thousand Stock Option Plan [Member] Two Thousand Stock Option Plan [Member] 2012 Equity Incentive Plan [Member] Two Thousand Twelve Equity Incentive Plan [Member] Two Thousand Twelve Equity Incentive Plan [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Shares of common stock reserved for future issuance Common Stock, Capital Shares Reserved for Future Issuance Contractual term of stock options Share-based Compensation Arrangement By Share-based Payment Award, Options Outstanding Contractual Term Contractual term of stock options. Plan expiration date Share-based Compensation Arrangement by Share-based Payment Award, Expiration Date Vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Requisite Service Period Options outstanding at end of year, number of options Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Options outstanding at end of year, weighted average exercise price Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Options outstanding at end of year, weighted average remaining contractual life (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Options exercisable at end of year, number of options Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Options exercisable at end of year, weighted average exercise price Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Options exercisable at end of year, weighted average remaining contractual life (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Number of shares available for future grants Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Compensation expense Share-based Payment Arrangement, Expense Fair value of stock options vested during the period Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, In Period, Fair Value Fair value of stock options vested during the period. Unrecognized total future compensation cost Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Unvested restricted stock at end of year, number of shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Unvested restricted stock at end of year, 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 Unrecognized total future compensation cost, net of forfeitures Employee service share based compensation nonvested awards total compensation cost not yet recognized net of forfeitures Unrecognized cost of unvested share-based compensation awards, net of forfeitures. Fair value of restricted stock vested during the period Share based compensation arrangement by share based payment award restricted stock vested in period fair value Fair value of restricted stock that vested during the period. Unrecognized total future compensation cost weighted average recognition period Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Schedule Of Earnings Per Share, Basic And Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Schedule of Investments [Line Items] Schedule of Investments [Line Items] Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Estimated Fair Value Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Available-for-sale Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Estimated Fair Value Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer Available-for-sale Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Unrealized Losses Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Estimated Fair Value Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Held-to-maturity Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Estimated Fair Value Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value Held-to-maturity Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Unrealized Losses Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table] Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table] Capitol Federal Savings Bank [Member] Subsidiaries [Member] Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] Tier 1 leverage, Actual Amount Tier One Leverage Capital Tier 1 leverage, Actual Ratio Tier One Leverage Capital to Average Assets Tier 1 leverage, For Capital Adequacy Purposes, Amount Tier One Leverage Capital Required for Capital Adequacy Tier 1 leverage, For Capital Adequacy Purposes, Ratio Tier One Leverage Capital Required for Capital Adequacy to Average Assets Tier 1 leverage, To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount Tier One Leverage Capital Required to be Well Capitalized Tier 1 leverage, To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio Tier One Leverage Capital Required to be Well Capitalized to Average Assets CET1 capital, Actual Amount Common Equity Tier One Capital CET1 capital, Actual Ratio Common Equity Tier One Capital Ratio CET1 capital, For Capital Adequacy Purposes, Amount Common Equity Tier One Capital Required for Capital Adequacy CET1 capital, For Capital Adequacy Purposes, Ratio Common Equity Tier 1 Capital, For Capital Adequacy Purposes, Ratio The minimum Common Equity Tier 1 Capital Ratio required for capital adequacy purposes as defined by the regulators. CET1 capital, To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount Common Equity Tier One Capital Required to be Well-Capitalized CET1 capital, To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio Common Equity Tier 1 Capital Ratio Required To Be Well Capitalized The Common Equity Tier 1 Capital Ratio required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action. Tier 1 capital, Actual Amount Tier One Risk Based Capital Tier 1 capital, Actual Ratio Tier One Risk Based Capital to Risk Weighted Assets Tier 1 capital, For Capital Adequacy Purposes, Amount Tier One Risk Based Capital Required for Capital Adequacy Tier 1 capital, For Capital Adequacy Purposes, Ratio Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets Tier 1 capital, To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount Tier One Risk Based Capital Required to be Well Capitalized Tier 1 capital, To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets Total capital, Actual Amount Capital Total capital, Actual Ratio Capital to Risk Weighted Assets Total capital, For Capital Adequacy Purposes, Amount Capital Required for Capital Adequacy Total capital, For Capital Adequacy Purposes, Ratio Capital Required for Capital Adequacy to Risk Weighted Assets Total capital, To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount Capital Required to be Well Capitalized Total capital, To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio Capital Required to be Well Capitalized to Risk Weighted Assets Selected Quarterly Financial Data (Unaudited) Quarterly Financial Information [Text Block] Summary Of Quarterly Data Quarterly Financial Information [Table Text Block] Financing Receivable, Allowance for Credit Loss [Table] Financing Receivable, Allowance for Credit Loss [Table] Financing Receivable, Allowance for Credit Loss [Line Items] Financing Receivable, Allowance for Credit Loss [Line Items] Beginning Balance Financing Receivable, Allowance for Credit Loss Charge-offs Financing Receivable, Allowance for Credit Loss, Writeoff Recoveries Financing Receivable, Allowance for Credit Loss, Recovery Provision for credit losses Provision for Loan, Lease, and Other Losses Ending Balance Weighted average credit score Weighted Average Credit Score Weighted Average Credit Score Weighted average LTV Weighted Average Loan To Value Ratio Weighted Average Loan To Value Ratio. Recorded Investment Impaired Financing Receivable, Recorded Investment Unpaid Principal Balance Impaired Financing Receivable, Unpaid Principal Balance Net purchase discount related to acquired loans Deferred Income Tax Expense Benefit Net Purchase Discounts on Acquired Loans The change during the period in the entity's deferred tax assets and liabilities attributable to net purchase discounts related to acquired loans. FHLB stock dividends Deferred Income Tax Expense Benefit FHLB Stock Dividends The change during the period in the entity's deferred tax assets and liabilities attributable to FHLB stock dividends. Salaries, deferred compensation and employee benefits Deferred Income Tax Expense Benefit Salaries Deferred Compensation and Employee Benefits The change during the period in the entity's deferred tax assets and liabilities attributable to salaries, deferred compensation, and employee benefits. Low income housing partnerships Deferred Income Tax Expense Benefit Low Income Housing Partnerships The change during the period in the entity's deferred tax assets and liabilities attributable to low income housing partnerships. Premises and equipment Deferred Income Tax Expense Benefit Fixed Assets The change during the period in the entity's deferred tax assets and liabilities attributable to fixed assets. Deposit intangible Deferred Income Tax Expense Benefit Deposit Intangible The change during the period in the entity's deferred tax assets and liabilities attributable to deposit intangibles. ACL Deferred Income Tax Expense Benefit Allowance For Credit Losses The change during the period in the entity's deferred tax assets and liabilities attributable to the allowance for credit losses. Other, net Deferred Other Tax Expense (Benefit) Deferred income tax expense Summary Of Significant Accounting Policies Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Schedule of Goodwill and Intangible Assets [Table] Schedule of Goodwill and Intangible Assets [Table] Schedule of Goodwill and Intangible Assets [Table] Schedule of Goodwill and Intangible Assets [Line Items] Schedule of Goodwill and Intangible Assets [Line Items] [Line Items] for Schedule of Goodwill and Intangible Assets [Table] Goodwill Balance Goodwill Goodwill, Acquired During Period Goodwill, Purchase Accounting Adjustments Goodwill, Purchase Accounting Adjustments Goodwill, Amortization Amortization Of Goodwill The aggregate expense charged against earnings to amortize goodwill Goodwill Balance Core Deposit and Other Intangibles Balance Finite-Lived Intangible Assets, Net Core Deposit and Other Intangibles, Acquired During Period Core Deposit and Other Intangibles, Purchase Accounting Adjustments Finite-Lived Intangible Assets, Purchase Accounting Adjustments Core Deposit and Other Intangibles, Amortization Amortization of Intangible Assets Core Deposit and Other Intangibles Balance Commitments And Contingencies Commitments and Contingencies Disclosure [Text Block] Unrealized gains (losses) on AFS securities arising during the period, deferred income taxes Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax Unrealized gains on securities reclassified from HTM to AFS during the period, deferred income taxes Other Comprehensive Income (Loss), Transfers from Held-to-maturity to Available-for-Sale Securities, Tax Changes in unrealized gains (losses) on cash flow hedges, deferred income taxes Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax, Portion Attributable to Parent Share-based Payment Arrangement, Disclosure [Abstract] Schedule of Employee Stock Ownership Plan (ESOP) Disclosures [Table] Schedule of Employee Stock Ownership Plan (ESOP) Disclosures [Table] Subsidiary, Sale of Stock [Axis] Sale of Stock [Axis] Sale of Stock, Name of Transaction [Domain] Sale of Stock [Domain] IPO [Member] IPO [Member] Corporate Reorganization [Member] Corporate Reorganization [Member] Corporate Reorganization [Member] Employee Stock Ownership Plan (ESOP) Disclosures [Line Items] Employee Stock Ownership Plan (ESOP) Disclosures [Line Items] Number of shares acquired by ESOP trust Number Shares Acquired By Employee Stock Ownership Plan Number of shares acquired by employee stock ownership plan. Number of shares acquired by ESOP post corporate reorganization Number Of Shares Acquired By Employee Stock Ownership Plan Post Corporate Reorganization Number Of Shares Acquired By Employee Stock Ownership Plan Post Corporate Reorganization ESOP loan maturity date Debt Instrument, Maturity Date Shares Held In Employee Stock Ownership Plan, Allocated Shares Held In Employee Stock Ownership Plan Allocated Number of allocated shares held by the Employee Stock Ownership Plan at balance sheet date. Allocated shares are shares that have been assigned to individual participant accounts based on a known formula. Shares Held In Employee Stock Ownership Plan, Committed-to-be-Released Employee Stock Ownership Plan (ESOP), Number of Committed-to-be-Released Shares Compensation expense related to the ESOP including dividends Employee Stock Ownership Plan ESOP Compensation Expense Including Dividends On Unallocated Shares In Excess Of Debt Service Payments Employee Stock Ownership Plan ESOP Compensation Expense Including Dividends On Unallocated Shares In Excess Of Debt Service Payments Portion of compensation expense related to the ESOP attributable to changes in Company stock price Portion Of Compensation Expense Related To ESOP Attributable To Changes In Company Stock Price Portion Of Compensation Expense Related To ESOP Attributable To Changes In Company Stock Price Dividends on unallocated ESOP shares in excess of debt service payments Employee Stock Ownership Plan (ESOP), Dividends Paid to ESOP Percentage of ESOP shares participant may diversify once age requirement is met Percentage Of Employee Stock Ownership Plan Shares Diversified Percentage of Employee Stock Ownership Plan shares diversified Required age of participant in order to diversify ESOP shares, years Age Period Of Diversified Employee Stock Ownership Plan Shares Age at which employee ESOP participants may begin to diversify their ESOP shares into other investments. Schedule Of Borrowed Funds [Table] Schedule Of Borrowed Funds [Table] Schedule Of Borrowed Funds [Table] Leverage Strategy [Member] Leverage Strategy [Member] Leverage Strategy [Member] Subordinated Debentures Subject to Mandatory Redemption [Member] Subordinated Debentures Subject to Mandatory Redemption [Member] Noninterest-bearing deposits Noninterest-bearing Deposit Liabilities, Domestic Time Deposits, $250,000 or more Time Deposits, at or Above FDIC Insurance Limit FHLB borrowings, outstanding balance FHLB Advances, Fixed Rate Federal Home Loan Bank, Advances, Maturities Summary, Fixed Rate FHLB Advances, Variable Rate Federal Home Loan Bank, Advances, Maturities Summary, Floating Rate FHLB line of credit, outstanding balance Long-term Line of Credit FHLB line of credit available for leverage strategy, maximum Federal Home Loan Bank, Advances, General Debt Obligations, Maximum Amount Available Expiration date for FHLB line of credit Line of Credit Facility, Expiration Date Interest rate swaps, notional amount Derivative Liability, Notional Amount Interest rate swaps, notional amount Derivative Asset, Notional Amount Interest rate swaps, remaining term to maturity Derivative, Average Remaining Maturity Interest rate swaps, fair value Derivative, Fair Value, Net Interest rate swaps, amount reclassified from AOCI Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net Interest rate swaps, future amount to be reclassified from AOCI Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred Interest rate swaps, amount of hedge ineffectiveness recognized Loss on Cash Flow Hedge Ineffectiveness Interest rate swaps, collateral posted Collateral Already Posted, Aggregate Fair Value Interest rate swaps, collateral held Derivative Asset, Fair Value of Collateral FHLB borrowings threshold percentage of regulatory assets F H L B Borrowings Threshold Percentage Of Regulatory Assets FHLB Borrowings Threshold Percentage Of Regulatory Assets FHLB borrowings threshold percentage of regulatory assets, temporary increase FHLB borrowings threshold percentage of regulatory assets, temporary increase Increased FHLB borrowing limit (as a percentage of regulatory assets) as approved by the FHLB president for one year. FHLB percentage of regulatory assets Fhlb Percentage Of Regulatory Assets FHLB advances as a percentage of total assets reported to regulator. Repurchase Agreements Repurchase agreements Weighted average rate of repurchase agreements Assets Sold under Agreements to Repurchase, Interest Rate Repurchase Agreements, Description of Potential Risks Repurchase Agreements, Securities Lending Transactions, and Repurchase-to-Maturity Transactions Accounted for as Secured Borrowings, Description of Potential Risks Statement of Cash Flows [Abstract] Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest FHLB stock dividends Originations of loans receivable held-for-sale (LHFS) Payments for Origination of Mortgage Loans Held-for-sale