Significant Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2024
Accounting Policies [Abstract]
Basis of Accounting, Policy [Policy Text Block]	Basis of Presentation: BankFinancial Corporation, a Maryland corporation headquartered in Burr Ridge, Illinois, is the owner of all of the issued and outstanding capital stock of BankFinancial, National Association (the “Bank”). The interim unaudited consolidated financial statements include the accounts and transactions of BankFinancial Corporation, the Bank, and the Bank’s wholly-owned subsidiaries, Financial Assurance Services, Inc. and BFIN Asset Recovery Company, LLC (collectively, the “Company”), and reflect all normal and recurring adjustments that are, in the opinion of management, considered necessary for a fair presentation of the financial condition and results of operations for the periods presented. Such adjustments are the only adjustments reflected in the accompanying financial statements. All significant intercompany accounts and transactions have been eliminated. The results of operations for the three and nine-month periods ended September 30, 2024 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2024 or for any other period. Certain information and note disclosures normally included in financial statements prepared in conformity with accounting principles generally accepted in the United States of America (“US GAAP”) have been condensed or omitted pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”).
Use of Estimates, Policy [Policy Text Block]	Use of Estimates: The preparation of the consolidated financial statements in conformity with US GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Although these estimates and assumptions are based on the best available information, actual information and actual results could differ from those estimates.
Financing Receivable, Fee and Interest Income [Policy Text Block]	Factored Receivables: The Company purchases invoices from its factoring customers in schedules or batches. These receivables are included in loans receivable on the Consolidated Statements of Financial Condition, and as commercial loans and leases in Note 4 - Loans Receivable. The face value of the invoices purchased or amount advanced is recorded by the Company as factored receivables, and the unadvanced portions of the invoices purchased, less fees, are considered customer reserves. The customer reserves are held to settle any payment disputes or collection shortfalls. Customer reserves may be used to pay customers’ obligations to various third parties as directed by the customer. Customer reserves are periodically released to or withdrawn by customers, and are reported as noninterest-bearing deposits in the Consolidated Statements of Financial Condition. The unpaid principal balances of these receivables were $2.3 million and $5.9 million at September 30, 2024 and December 31, 2023, respectively, and are included in commercial loans and leases. The customer reserves associated with the factored receivables were $675,000 and $2.1 million at September 30, 2024 and December 31, 2023, respectively. Factoring fees are recognized in interest income as incurred by the customer and deducted from the customer's reserve balances. Other factoring-related fees, which include wire transfer fees, broker fees, and other similar fees, are reported by the Company as loan servicing fees in noninterest income.
Interest-bearing Deposits in Other Financial Institutions [Policy Text Block]	Interest-Bearing Time Deposits in other Financial Institutions: Interest-bearing time deposits in other financial institutions are carried at cost. Prior year financial statement disclosures reported interest-bearing time deposits in other financial institutions, maturing in 90 days or more, with Securities.
Reclassification, Comparability Adjustment [Policy Text Block]	Reclassifications: Certain reclassifications have been made in the prior period’s financial statements to conform them to the current period’s presentation with no impact on previously reported net income or stockholders' equity. These unaudited consolidated financial statements should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2023, as filed with the SEC.
New Accounting Pronouncements, Policy [Policy Text Block]	**Newly Issued Not* Yet Effective Accounting Standards:*** In December 2023, the FASB issued Accounting Standards Update (“ASU”) 2023-09, Income Tax (Topic 740): Improvements to Income Tax Disclosures. The amendments expand the disclosure requirements of income taxes, primarily related to the income tax rate reconciliation and income taxes paid. The guidance also eliminates certain existing disclosure requirements related to uncertain tax positions and unrecognized deferred income tax liabilities. The amendments are effective for fiscal years beginning after December 15, 2024, and interim periods within fiscal years beginning after December 15, 2025. Earlier adoption is permitted. The adoption of the guidance is not expected to have a material impact on the Company’s consolidated financial statements.

Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2024

Basis of Accounting, Policy [Policy Text Block]

Basis of Presentation: BankFinancial Corporation, a Maryland corporation headquartered in Burr Ridge, Illinois, is the owner of all of the issued and outstanding capital stock of BankFinancial, National Association (the “Bank”). The interim unaudited consolidated financial statements include the accounts and transactions of BankFinancial Corporation, the Bank, and the Bank’s wholly-owned subsidiaries, Financial Assurance Services, Inc. and BFIN Asset Recovery Company, LLC (collectively, the “Company”), and reflect all normal and recurring adjustments that are, in the opinion of management, considered necessary for a fair presentation of the financial condition and results of operations for the periods presented. Such adjustments are the only adjustments reflected in the accompanying financial statements. All significant intercompany accounts and transactions have been eliminated. The results of operations for the three and nine-month periods ended September 30, 2024 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2024 or for any other period.

Certain information and note disclosures normally included in financial statements prepared in conformity with accounting principles generally accepted in the United States of America (“US GAAP”) have been condensed or omitted pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”).

Use of Estimates, Policy [Policy Text Block]

Use of Estimates: The preparation of the consolidated financial statements in conformity with US GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Although these estimates and assumptions are based on the best available information, actual information and actual results could differ from those estimates.

Financing Receivable, Fee and Interest Income [Policy Text Block]

Factored Receivables: The Company purchases invoices from its factoring customers in schedules or batches. These receivables are included in loans receivable on the Consolidated Statements of Financial Condition, and as commercial loans and leases in Note 4 - Loans Receivable. The face value of the invoices purchased or amount advanced is recorded by the Company as factored receivables, and the unadvanced portions of the invoices purchased, less fees, are considered customer reserves. The customer reserves are held to settle any payment disputes or collection shortfalls. Customer reserves may be used to pay customers’ obligations to various third parties as directed by the customer. Customer reserves are periodically released to or withdrawn by customers, and are reported as noninterest-bearing deposits in the Consolidated Statements of Financial Condition. The unpaid principal balances of these receivables were $2.3 million and $5.9 million at September 30, 2024 and December 31, 2023, respectively, and are included in commercial loans and leases. The customer reserves associated with the factored receivables were $675,000 and $2.1 million at September 30, 2024 and December 31, 2023, respectively.

Factoring fees are recognized in interest income as incurred by the customer and deducted from the customer's reserve balances. Other factoring-related fees, which include wire transfer fees, broker fees, and other similar fees, are reported by the Company as loan servicing fees in noninterest income.

Interest-bearing Deposits in Other Financial Institutions [Policy Text Block]

Interest-Bearing Time Deposits in other Financial Institutions: Interest-bearing time deposits in other financial institutions are carried at cost. Prior year financial statement disclosures reported interest-bearing time deposits in other financial institutions, maturing in 90 days or more, with Securities.

Reclassification, Comparability Adjustment [Policy Text Block]

Reclassifications: Certain reclassifications have been made in the prior period’s financial statements to conform them to the current period’s presentation with no impact on previously reported net income or stockholders' equity.

These unaudited consolidated financial statements should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2023, as filed with the SEC.

New Accounting Pronouncements, Policy [Policy Text Block]

Newly Issued Not Yet Effective Accounting Standards: In December 2023, the FASB issued Accounting Standards Update (“ASU”) 2023-09, Income Tax (Topic 740): Improvements to Income Tax Disclosures. The amendments expand the disclosure requirements of income taxes, primarily related to the income tax rate reconciliation and income taxes paid. The guidance also eliminates certain existing disclosure requirements related to uncertain tax positions and unrecognized deferred income tax liabilities. The amendments are effective for fiscal years beginning after December 15, 2024, and interim periods within fiscal years beginning after December 15, 2025. Earlier adoption is permitted. The adoption of the guidance is not expected to have a material impact on the Company’s consolidated financial statements.