Fair Value of Assets and Liabilities - Fair Value of Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. government agency securities, mortgage-backed securities, obligations of states and political subdivisions, collateralized mortgage obligations, and corporate bonds	$ 95,635	$ 98,194
Fair Value, Recurring \| Assets:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. government agency securities, mortgage-backed securities, obligations of states and political subdivisions, collateralized mortgage obligations, and corporate bonds	95,635	98,194
Fair Value, Recurring \| Assets: \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. government agency securities, mortgage-backed securities, obligations of states and political subdivisions, collateralized mortgage obligations, and corporate bonds	0	0
Fair Value, Recurring \| Assets: \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. government agency securities, mortgage-backed securities, obligations of states and political subdivisions, collateralized mortgage obligations, and corporate bonds	95,635	98,194
Fair Value, Recurring \| Assets: \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. government agency securities, mortgage-backed securities, obligations of states and political subdivisions, collateralized mortgage obligations, and corporate bonds	$ 0	$ 0

Amount of 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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FIVE STAR BANCORP 10-Q