Employee Benefits - Additional information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Jun. 30, 2019
Number of shares committed to be released each year, ESOP		11,924	11,924
Unearned compensation for ESOP		$ 3,163,000	$ 2,146,000
Defined Benefit Plan, Plan Assets, Contributions by Employer		189,000	198,000
Deferred Compensation Liability Current And Noncurrent		1,729,000	1,667,000
Scenario Forecast [Member]
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant	$ 200,000
Pentegra DB Plan [Member]
Defined Benefit Plan, Plan Assets, Contributions by Employer		200,000
Maximum employer contribution percentage in defined benefit plan				5.00%
Pension Cost (Reversal of Cost)		200,000	300,000
Salary Continuation Plan [Member] | Supplemental Employee Retirement Plan [Member]
Liability, Defined Benefit Plan		$ 634,000	$ 607,000
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		5.00%	5.00%
Employee salary incremental percent		3.00%	3.00%
Defined Contribution Plan, Cost		$ 82,000	$ 73,000
Executive Supplemental Retirement Plan | Supplemental Employee Retirement Plan [Member]
Pension Cost (Reversal of Cost)		6,000	8,000
Liability, Defined Benefit Plan		$ 90,000	$ 132,000
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		6.25%	6.25%
Endorsement Method Split Dollar Plan [Member] | Supplemental Employee Retirement Plan [Member]
Pension Cost (Reversal of Cost)		$ 1,000	$ 1,000
Liability, Defined Benefit Plan		35,000	34,000
Deferred Directors Supplemental Retirement Plan [Member] | Supplemental Employee Retirement Plan [Member]
Pension Cost (Reversal of Cost)		63,000	63,000
Liability, Defined Benefit Plan		$ 550,000	$ 573,000
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		625.00%	625.00%
Deferred Compensation Liability Current And Noncurrent		$ 420,000	$ 321,000
First Seacoast Bank Employee Stock Ownership Plan [Member]
Number of shares committed to be released each year, ESOP		11,924
Employee stock option compensation recognized		$ 115,000	89,000
Unearned compensation for ESOP		2,000,000.0	2,100,000
Employee stock option unallocated shares fair value		$ 2,200,000	1,900,000
Employee stock option plan [Member]
Stock Repurchase		238,473
Remaining Loan Term		17 years 6 months
Percentage of Purchase price common stock		100.00%
Remaining Principal Balance of Debt		$ 2,100,000	$ 2,200,000