Significant Accounting Policies (Policies)	3 Months Ended
Mar. 31, 2024
Accounting Policies [Abstract]
Basis of Accounting, Policy [Policy Text Block]	Basis of Presentation The accompanying unaudited consolidated financial statements of the Company have been prepared in accordance with GAAP for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include information or footnotes necessary for a complete presentation of financial position, results of operations, and cash flows in conformity with GAAP. However, in the opinion of management, all adjustments (consisting of normal recurring adjustments) necessary for a fair presentation of the financial statements have been included. The results of operations for the three month period ended March 31, 2024 are not necessarily indicative of the results that may be expected for the entire fiscal year. These statements should be read in conjunction with the Company’s audited consolidated financial statements for the year ended December 31, 2023, including the notes thereto, which were included as part of the Company’s Annual Report.
Nature of Operations Policy [Policy Text Block]	Nature of Operations The Company is a financial holding company, headquartered in Baton Rouge, Louisiana that provides full banking services, excluding trust services, through its wholly-owned banking subsidiary, Investar Bank, National Association, a national bank, primarily to meet the needs of individuals, professionals and small to medium-sized businesses. The Company’s primary markets are in south Louisiana, southeast Texas and Alabama. At March 31, 2024 , the Company operated 20 full service branches located in Louisiana, two full service branches located in Texas and six full service branches located in Alabama and had 323 full-time equivalent employees.
Consolidation, Policy [Policy Text Block]	Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary, the Bank. All significant intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates, Policy [Policy Text Block]	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements as well as the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates, and such differences could be material. Material estimates that are particularly susceptible to significant change relate to the determination of the allowance for credit losses. While management uses available information to recognize credit losses on loans, future additions to the allowance may be necessary based on changes in economic conditions, changes in conditions of our borrowers’ industries or changes in the condition of individual borrowers. The Company adopted ASU 2016-13 effective January 1, 2023, which changed how the Company accounts for the allowance for credit losses. In addition, regulatory agencies, as an integral part of their examination process, periodically review the Company’s allowance for credit losses. Such agencies may require the Company to recognize additions to the allowance based on their judgments about information available to them at the time of their examination. Because of these factors, it is reasonably possible that the allowance for credit losses may change materially in the near term. However, the amount of the change that is reasonably possible cannot be estimated. Other estimates that are susceptible to significant change in the near term relate to the allowance for off-balance sheet credit losses, the fair value of stock-based compensation awards, the determination of other-than-temporary impairments of securities, and the fair value of financial instruments and goodwill. Rapidly changing inflation rates and rising interest rates have made certain estimates more challenging, including those discussed above.
Reclassification, Comparability Adjustment [Policy Text Block]	Reclassifications Certain reclassifications have been made to prior period balances to conform to the current period presentation.
New Accounting Pronouncements, Policy [Policy Text Block]	Recent Accounting Pronouncements FASB “Disclosure Improvements” Update No. 2023-06 (“ASU 2023-06”). In October 2023, the FASB issued ASU 2023-06, which amends the disclosure or presentation requirements related to various topics. The amendment is intended to align GAAP with the SEC’s regulations. ASU 2023-06 is required to be applied prospectively, and early adoption is prohibited. For reporting entities subject to the SEC’s existing disclosure requirements, the effective dates of ASU 2023-06 will be the date on which the SEC’s removal of that related disclosure requirement from Regulation S-X or Regulation S-K becomes effective. If by June 30, 2027, the SEC has not removed the applicable requirement from Regulation S-X or Regulation S-K, the pending content of the related amendment will be removed and will not become effective for any entities. ASU 2023-06 is not expected to have a material impact on the Company’s consolidated financial statements. FASB ASC Topic 740 “Income Taxes - Improvements to Income Tax Disclosures” Update No. 2023-09 (“ASU 2023-09”). In December 2023, the FASB issued ASU 2023-09, which enhances the transparency and decision usefulness of income tax disclosures. ASU 2023-09 requires disclosure of additional categories of information about federal, state and foreign income taxes in the rate reconciliation table and requires companies to provide more information about the reconciling items in some categories if a quantitative threshold is met. The adoption of ASU 2023-09 is effective for fiscal years beginning after December 15, 2024 and is not expected to have a material impact on the Company’s consolidated financial statements.

Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2024

Basis of Accounting, Policy [Policy Text Block]

Basis of Presentation

The accompanying unaudited consolidated financial statements of the Company have been prepared in accordance with GAAP for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include information or footnotes necessary for a complete presentation of financial position, results of operations, and cash flows in conformity with GAAP. However, in the opinion of management, all adjustments (consisting of normal recurring adjustments) necessary for a fair presentation of the financial statements have been included. The results of operations for the three month period ended March 31, 2024 are not necessarily indicative of the results that may be expected for the entire fiscal year. These statements should be read in conjunction with the Company’s audited consolidated financial statements for the year ended December 31, 2023, including the notes thereto, which were included as part of the Company’s Annual Report.

Nature of Operations Policy [Policy Text Block]

Nature of Operations

The Company is a financial holding company, headquartered in Baton Rouge, Louisiana that provides full banking services, excluding trust services, through its wholly-owned banking subsidiary, Investar Bank, National Association, a national bank, primarily to meet the needs of individuals, professionals and small to medium-sized businesses. The Company’s primary markets are in south Louisiana, southeast Texas and Alabama. At March 31, 2024 , the Company operated 20 full service branches located in Louisiana, two full service branches located in Texas and six full service branches located in Alabama and had 323 full-time equivalent employees.

Consolidation, Policy [Policy Text Block]

Principles of Consolidation

The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary, the Bank. All significant intercompany accounts and transactions have been eliminated in consolidation.

Use of Estimates, Policy [Policy Text Block]

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements as well as the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates, and such differences could be material.

Material estimates that are particularly susceptible to significant change relate to the determination of the allowance for credit losses. While management uses available information to recognize credit losses on loans, future additions to the allowance may be necessary based on changes in economic conditions, changes in conditions of our borrowers’ industries or changes in the condition of individual borrowers. The Company adopted ASU 2016-13 effective January 1, 2023, which changed how the Company accounts for the allowance for credit losses. In addition, regulatory agencies, as an integral part of their examination process, periodically review the Company’s allowance for credit losses. Such agencies may require the Company to recognize additions to the allowance based on their judgments about information available to them at the time of their examination. Because of these factors, it is reasonably possible that the allowance for credit losses may change materially in the near term. However, the amount of the change that is reasonably possible cannot be estimated.

Other estimates that are susceptible to significant change in the near term relate to the allowance for off-balance sheet credit losses, the fair value of stock-based compensation awards, the determination of other-than-temporary impairments of securities, and the fair value of financial instruments and goodwill. Rapidly changing inflation rates and rising interest rates have made certain estimates more challenging, including those discussed above.

Reclassification, Comparability Adjustment [Policy Text Block]

Reclassifications

Certain reclassifications have been made to prior period balances to conform to the current period presentation.

New Accounting Pronouncements, Policy [Policy Text Block]

Recent Accounting Pronouncements

FASB “Disclosure Improvements” Update No. 2023-06 (“ASU 2023-06”). In October 2023, the FASB issued ASU 2023-06, which amends the disclosure or presentation requirements related to various topics. The amendment is intended to align GAAP with the SEC’s regulations. ASU 2023-06 is required to be applied prospectively, and early adoption is prohibited. For reporting entities subject to the SEC’s existing disclosure requirements, the effective dates of ASU 2023-06 will be the date on which the SEC’s removal of that related disclosure requirement from Regulation S-X or Regulation S-K becomes effective. If by June 30, 2027, the SEC has not removed the applicable requirement from Regulation S-X or Regulation S-K, the pending content of the related amendment will be removed and will not become effective for any entities. ASU 2023-06 is not expected to have a material impact on the Company’s consolidated financial statements.

FASB ASC Topic 740 “Income Taxes - Improvements to Income Tax Disclosures” Update No. 2023-09 (“ASU 2023-09”). In December 2023, the FASB issued ASU 2023-09, which enhances the transparency and decision usefulness of income tax disclosures. ASU 2023-09 requires disclosure of additional categories of information about federal, state and foreign income taxes in the rate reconciliation table and requires companies to provide more information about the reconciling items in some categories if a quantitative threshold is met. The adoption of ASU 2023-09 is effective for fiscal years beginning after December 15, 2024 and is not expected to have a material impact on the Company’s consolidated financial statements.