Basis of Presentation	9 Months Ended
Sep. 30, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation – The unaudited consolidated financial statements include the accounts of Business First Bancshares, Inc. (the “Company”) and its five direct, wholly-owned subsidiaries, b1BANK (the “Bank”), Coastal Commerce Statutory Trust I, Progressive Statutory Trust I, Progressive Statutory Trust II, and b1Capital, Inc.; and the Bank’s wholly-owned subsidiaries, Business First Insurance, LLC, Smith Shellnut Wilson, LLC ("SSW"), Waterstone LSP, LLC ("Waterstone"), and b1 Securities, LLC ("b1Securities"). The Bank operates out of full-service banking centers and loan production offices in markets across Louisiana, the Dallas/Fort Worth metroplex and Houston, Texas. As a state bank, it is subject to regulation by the Office of Financial Institutions (“OFI”), State of Louisiana, and the Federal Deposit Insurance Corporation (“FDIC”) and undergoes periodic examinations by these agencies. The Company is also regulated by the Federal Reserve and is subject to periodic examinations. In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments necessary to present fairly the financial results for the periods presented, and all such adjustments are of a normal recurring nature. All material intercompany transactions are eliminated. The results of operations for the interim periods are not necessarily indicative of the results to be expected for the entire year. These interim consolidated financial statements have been prepared according to the rules and regulations of the Securities and Exchange Commission and, therefore, certain information and footnote disclosures normally presented in accordance with United States (“U.S.”) generally accepted accounting principles (“GAAP”) have been omitted or abbreviated. These interim financial statements should be read in conjunction with the audited consolidated financial statements and footnote disclosures for the Company’s previously filed Form 10-K for the year ended December 31, 2025. Preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying disclosures. These estimates are based on management’s best knowledge of current events and actions the Company may undertake in the future. Critical accounting estimates that are particularly susceptible to significant change for the Company include the determination of the acquired loans, allowance for credit losses and purchase accounting adjustments (other than loans). Other estimates include goodwill, fair value of financial instruments, investment securities and the assessment of income taxes. Management does not anticipate any material changes to estimates in the near term. Factors that may cause sensitivity to the aforementioned estimates include but are not limited to: external market factors such as market interest rates and employment rates, changes to operating policies and procedures, economic conditions in the Company’s markets, and changes in applicable banking regulations. Actual results may ultimately differ from estimates. Accounting Standards Adopted in Current Period ASU 2025-08, "Financial Instruments – Credit Losses (Topic 326), Purchased Loans.” The updates in ASU 2025-08 amend the guidance in ASC 326 on the accounting for certain purchased loans. Under the ASU, entities must account for acquired loans (excluding credit cards) that meet certain criteria at acquisition (“purchased seasoned loans”) by recognizing them at their purchase price plus an allowance for expected credit losses (i.e., the gross-up approach). All non-purchased credit deteriorated (“non-PCD”) loans (excluding credit cards) that are acquired in a business combination are deemed seasoned. Other non-PCD loans (excluding credit cards) are seasoned if they were purchased at least 90 days after origination and the acquirer was not involved in the origination of the loans. The ASU’s amendments align the accounting for purchased seasoned loans with the treatment of financial assets purchased with more-than-insignificant credit deterioration since origination (“PCD assets”). The Company early adopted the amendments effective January 1, 2026, on a prospective basis. The Progressive acquisition disclosures contained in Note 2, as well as the allowance measurements reflected in Note 5 incorporate the updated guidance. Accounting Standards Not Yet Adopted None Reclassifications Certain reclassifications may have been made to conform to reporting in 2026. These reclassifications did not materially impact the Company's consolidated financial statements.

The unaudited consolidated financial statements include the accounts of Business First Bancshares, Inc. (the “Company”) and its five direct, wholly-owned subsidiaries, b1BANK (the “Bank”), Coastal Commerce Statutory Trust I, Progressive Statutory Trust I, Progressive Statutory Trust II, and b1Capital, Inc.; and the Bank’s wholly-owned subsidiaries, Business First Insurance, LLC, Smith Shellnut Wilson, LLC ("SSW"), Waterstone LSP, LLC ("Waterstone"), and b1 Securities, LLC ("b1Securities"). The Bank operates out of full-service banking centers and loan production offices in markets across Louisiana, the Dallas/Fort Worth metroplex and Houston, Texas. As a state bank, it is subject to regulation by the Office of Financial Institutions (“OFI”), State of Louisiana, and the Federal Deposit Insurance Corporation (“FDIC”) and undergoes periodic examinations by these agencies. The Company is also regulated by the Federal Reserve and is subject to periodic examinations.

In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments necessary to present fairly the financial results for the periods presented, and all such adjustments are of a normal recurring nature. All material intercompany transactions are eliminated. The results of operations for the interim periods are not necessarily indicative of the results to be expected for the entire year.

These interim consolidated financial statements have been prepared according to the rules and regulations of the Securities and Exchange Commission and, therefore, certain information and footnote disclosures normally presented in accordance with United States (“U.S.”) generally accepted accounting principles (“GAAP”) have been omitted or abbreviated. These interim financial statements should be read in conjunction with the audited consolidated financial statements and footnote disclosures for the Company’s previously filed Form 10-K for the year ended December 31, 2025.

Preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying disclosures. These estimates are based on management’s best knowledge of current events and actions the Company may undertake in the future. Critical accounting estimates that are particularly susceptible to significant change for the Company include the determination of the acquired loans, allowance for credit losses and purchase accounting adjustments (other than loans). Other estimates include goodwill, fair value of financial instruments, investment securities and the assessment of income taxes. Management does not anticipate any material changes to estimates in the near term. Factors that may cause sensitivity to the aforementioned estimates include but are not limited to: external market factors such as market interest rates and employment rates, changes to operating policies and procedures, economic conditions in the Company’s markets, and changes in applicable banking regulations. Actual results may ultimately differ from estimates.

ASU 2025-08, "Financial Instruments – Credit Losses (Topic 326), Purchased Loans.” The updates in ASU 2025-08 amend the guidance in ASC 326 on the accounting for certain purchased loans. Under the ASU, entities must account for acquired loans (excluding credit cards) that meet certain criteria at acquisition (“purchased seasoned loans”) by recognizing them at their purchase price plus an allowance for expected credit losses (i.e., the gross-up approach). All non-purchased credit deteriorated (“non-PCD”) loans (excluding credit cards) that are acquired in a business combination are deemed seasoned. Other non-PCD loans (excluding credit cards) are seasoned if they were purchased at least 90 days after origination and the acquirer was not involved in the origination of the loans. The ASU’s amendments align the accounting for purchased seasoned loans with the treatment of financial assets purchased with more-than-insignificant credit deterioration since origination (“PCD assets”).

The Company early adopted the amendments effective January 1, 2026, on a prospective basis. The Progressive acquisition disclosures contained in Note 2, as well as the allowance measurements reflected in Note 5 incorporate the updated guidance.