Nature of Business and Basis of Presentation (Policies)	9 Months Ended
Nature of Business and Basis of Presentation (Policies)	Sep. 30, 2019
Accounting Policies [Abstract]
Business Activity	Business Activity *Southern First Bancshares, Inc.* (the “Company”) is a South Carolina corporation that owns all of the capital stock of Southern First Bank (the “Bank”) and all of the stock of Greenville First Statutory Trust I and II (collectively, the “Trusts”). The Trusts are special purpose non-consolidated entities organized for the sole purpose of issuing trust preferred securities. The Bank's primary federal regulator is the Federal Deposit Insurance Corporation (the “FDIC”). The Bank is also regulated and examined by the South Carolina Board of Financial Institutions. The Bank is primarily engaged in the business of accepting demand deposits and savings deposits insured by the FDIC, and providing commercial, consumer and mortgage loans to the general public.
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles (“GAAP”) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all the information and footnotes required by accounting principles generally accepted in the United States of America for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation have been included. Operating results for the three and nine month periods ended September 30, 2019 are not necessarily indicative of the results that may be expected for the year ending December 31, 2019. For further information, refer to the consolidated financial statements and footnotes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018 as filed with the Securities and Exchange Commission (“SEC”) on February 28, 2019. The consolidated financial statements include the accounts of the Company and the Bank. In accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 810, “Consolidation,” the financial statements related to the Trusts have not been consolidated.
Business Segments	Business Segments In determining proper segment definition, the Company considers the materiality of a potential segment and components of the business about which financial information is available and regularly evaluated, relative to a resource allocation and performance assessment. The Company accounts for intersegment revenues and expenses as if the revenue/expense transactions were generated to third parties, that is, at current market prices. Please refer to “Note 10 – Reportable Segments” for further information on the reporting for the Company’s three business segments.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America, or GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amount of income and expenses during the reporting periods. Actual results could differ from those estimates. Material estimates that are particularly susceptible to significant change in the near term relate to the determination of the allowance for loan losses, real estate acquired in the settlement of loans, fair value of financial instruments, evaluating other-than-temporary-impairment of investment securities and valuation of deferred tax assets.
Reclassifications	Reclassifications Certain amounts, previously reported, have been reclassified to state all periods on a comparable basis and had no effect on shareholders’ equity or net income.
Subordinated Debentures	Subordinated Debentures On September 30, 2019, the Company entered into Subordinated Note Purchase Agreements (collectively, the “Purchase Agreement”) with certain qualified institutional buyers and accredited investors (the “Purchasers”) pursuant to which the Company sold and issued $23.0 million in aggregate principal amount of its 4.75% Fixed-to-Floating Rate Subordinated Notes due 2029 (the “Notes”). The Notes were offered and sold by the Company to eligible purchasers in a private offering in reliance on the exemption from the registration requirements of Section 4(a)(2) of the Securities Act of 1933, as amended (the “Securities Act”) and the provisions of Regulation D promulgated thereunder (the “Private Placement”). The Company intends to use the proceeds from the offering, which were approximately $22.5 million, for general corporate purposes, including providing capital to the Bank and supporting organic growth. The Notes have a ten-year term and, from and including the date of issuance to but excluding September 30, 2024, will bear interest at a fixed annual rate of 4.75%, payable semi-annually in arrears, for the first five years of the term. From and including September 30, 2024 to but excluding the maturity date or early redemption date, the interest rate shall reset quarterly to an interest rate per annum equal to a benchmark rate (which is expected to be Three-Month Term SOFR) plus 340.8 basis points, payable quarterly in arrears. As provided in the Notes, the interest rate on the Notes during the applicable floating rate period may be determined based on a rate other than Three-Month Term SOFR. The Notes are redeemable, in whole or in part, on September 30, 2024, on any interest payment date thereafter, and at any time upon the occurrence of certain events. The Purchase Agreement contains certain customary representations, warranties and covenants made by the Company, on the one hand, and the Purchasers, severally and not jointly, on the other hand. On September 30, 2019, in connection with the sale and issuance of the Notes, the Company entered into a Registration Rights Agreement (the “Registration Rights Agreement”) with the Purchasers. Under the terms of the Registration Rights Agreement, the Company has agreed to take certain actions to provide for the exchange of the Notes for subordinated notes that are registered under the Securities Act and have substantially the same terms as the Notes (the “Exchange Notes”). Under certain circumstances, if the Company fails to meet its obligations under the Registration Rights Agreement, it would be required to pay additional interest to the holders of the Notes. The Notes were issued under an Indenture, dated September 30, 2019 (the “Indenture”), by and between the Company and UMB Bank, National Association, as trustee. The Notes are not subject to any sinking fund and are not convertible into or, other than with respect to the Exchange Notes, exchangeable for any other securities or assets of the Company or any of its subsidiaries. The Notes are not subject to redemption at the option of the holder. The Notes are unsecured, subordinated obligations of the Company only and are not obligations of, and are not guaranteed by, any subsidiary of the Company. The Notes rank junior in right to payment to the Company’s current and future senior indebtedness. The Notes are intended to qualify as Tier 2 capital for regulatory capital purposes for the Company.
Subsequent Events	Subsequent Events Subsequent events are events or transactions that occur after the balance sheet date but before financial statements are issued. Recognized subsequent events are events or transactions that provide additional evidence about conditions that existed at the date of the balance sheet, including the estimates inherent in the process of preparing financial statements. Non-recognized subsequent events are events that provide evidence about conditions that did not exist at the date of the balance sheet but arose after that date. On October 4, 2019, the Company sold its Health Savings Account (“HSA”) deposit accounts, which totaled $6.2 million at September 30, 2019, to a nationwide HSA servicer and recognized a gain of approximately $745,000 from the sale. Also subsequent to September 30, 2019, the Company sold $30.3 million of investment securities from its existing investment portfolio, recognizing a gain of approximately $718,000. On October 11, 2019, the Company paid off $25.0 million of FHLB advances with an average cost of 3.36% and incurred a prepayment penalty of $1.5 million.
Adoption of New Accounting Standards	Adoption of New Accounting Standards In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842)”. The guidance in the update supersedes the requirements in ASC Topic 840, Leases. The guidance is intended to increase transparency and comparability among organizations by recognizing right-of-use assets and lease liabilities on the balance sheet. For public companies, this update was effective for interim and annual periods beginning after December 15, 2018. The Company adopted this guidance in the first quarter of 2019. Upon adoption, the Company elected a practical expedient which allows existing leases to retain their classification as operating leases. The Company has also elected to not recognize right-of-use assets and lease liabilities arising from short-term leases. Implementation of the guidance resulted in the recording of a right-of-use asset and lease liability on the balance sheet; however it does not have a material impact on the Company's other consolidated financial statements. See additional disclosures in Note 8.
Newly Issued, But Not Yet Effective Accounting Standards	Newly Issued, But Not Yet Effective Accounting Standards In June 2016, the FASB issued ASU 2016-13, “Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments”. Among other things, ASU 2016-13 requires the measurement of all expected credit losses for financial assets held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. Financial institutions and other organizations will now use forward-looking information to form their credit loss estimates. Many of the loss estimation techniques applied today will still be permitted, although the inputs to those techniques will change to reflect the full amount of expected credit losses. In addition, ASU 2016-13 amends the accounting for credit losses on debt securities and purchased financial assets with credit deterioration. ASU 2016-13 is effective for all annual and interim periods beginning after December 31, 2019, with early adoption permitted for fiscal years beginning after December 15, 2018. Adoption will be applied through a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. The Company has established a team of individuals from credit, finance and risk management to evaluate the requirements of the new standard and the impact it will have on its processes. The implementation plan has progressed through the initial design, build, and testing phase and, in the first quarter of 2019, the Company began running parallel models. While the Company continues to evaluate the impact the new guidance will have on its financial position and results of operations, it currently expects the new guidance may result in an increase to its allowance for credit losses given the change to estimated losses over the contractual life of the loan portfolio. The amount of any change to the allowance is still under review and will depend, in part, upon the composition of our loan portfolio at the adoption date as well as economic conditions and loss forecasts at that date. On October 16, 2019, FASB voted to delay the effective date of this ASU for smaller reporting companies, such as the Company, until fiscal years beginning after December 15, 2022. Other accounting standards that have been issued or proposed by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the consolidated financial statements upon adoption.