v3.25.0.1

SECURITIES - Narrative (Details)	12 Months Ended
SECURITIES - Narrative (Details)	Dec. 31, 2024 USD ($) security	Dec. 31, 2023 USD ($) security	Dec. 31, 2022 USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, AFS, allowance for credit loss	$ 0	$ 0
Accrued interest receivable	$ 5,000,000.0	$ 5,200,000
Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss, Current, Statement of Financial Position [Extensible Enumeration]	Interest receivable	Interest receivable
Total loans	$ 5,407,231,000	$ 5,170,042,000
Debt securities, HTM, credit loss exposure	201,000	205,000
Debt securities, HTM, accrued interest, after allowance for credit loss	$ 3,100,000	$ 3,400,000
Debt Securities, Held-to-Maturity, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]	Interest receivable	Interest receivable
Debt securities, HTM, excluding accrued interest, nonaccrual	$ 0	$ 0
Carrying value of securities pledged to public deposits	$ 1,089,000,000.000	$ 1,095,000,000.000
Number of security portfolio \| security	1,063	1,125
Equity securities	$ 15,684,000	$ 0
Change in value of equity securities	(78,000)	0	$ 0
Total Past Due
Debt and Equity Securities, FV-NI [Line Items]
Total loans	0
Securities HTM, excluding accrued interest, past due 30 days	0
AFS Securities
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, AFS, allowance for credit loss	$ 0	$ 0

Amount of credit loss exposure of held to maturity securities.

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Securities held to maturity past due 30 days.

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Amount, after allowance for credit loss, of accrued interest on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current.

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Amount excluding accrued interest, of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, after allowance for credit loss, of accrued interest on investment in debt security measured at amortized cost (held-to-maturity).

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Amount excluding accrued interest, of investment in debt security measured at amortized cost (held-to-maturity) on nonaccrual status.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair value of liabilities arising from or related to a financial instrument held by the entity for its own account (proprietary securities) which has been pledged to counterparties.

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FIRST BANCSHARES INC /MS/ 10-K