Employee Benefits - Additional information (Detail) - USD ($)				12 Months Ended
	Jul. 01, 2022	Feb. 10, 2022	Jul. 01, 2021	Dec. 31, 2022	Dec. 31, 2021	Jun. 30, 2019	May 26, 2022
Number of shares committed to be released each year, ESOP				11,924	11,924
Unearned compensation for ESOP				$ 2,637,000	$ 3,163,000
Defined Benefit Plan, Plan Assets, Contributions by Employer				202,000	189,000
Pension Cost (Reversal of Cost)				1,300,000
Deferred Compensation Liability Current And Noncurrent				1,830,000	1,729,000
Funded percentage							100.00%
Withdrawal liability amount				1,500,000
Withdrawal liability paid				200,000
Pension Plan [Member]
Percentage of funding status	96.24%		104.99%
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)				1,500,000	200,000
Salary Continuation Plan [Member] | Supplemental Employee Retirement Plan [Member]
Liability, Defined Benefit Plan				$ 660,000	$ 634,000
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	$ 82,000
Executive Supplemental Retirement Plan | Supplemental Employee Retirement Plan [Member]
Pension Cost (Reversal of Cost)				3,000	6,000
Liability, Defined Benefit Plan				$ 47,000	$ 90,000
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)				$ 0	$ 1,000
Liability, Defined Benefit Plan				34,000	35,000
Deferred Directors Supplemental Retirement Plan [Member] | Supplemental Employee Retirement Plan [Member]
Pension Cost (Reversal of Cost)				75,000	63,000
Liability, Defined Benefit Plan				$ 537,000	$ 550,000
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate				6.25%	6.25%
Defined Contribution Plan, Cost		$ 20,000
Revised fixed annual retirement benefits, payable		$ 200,000
Deferred Compensation Liability Current And Noncurrent				$ 553,000	$ 420,000
Previous final base fee, percentage		70.00%
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				$ 124,000	115,000
Unearned compensation for ESOP				1,900,000	2,000,000.0
Employee stock option unallocated shares fair value				$ 1,800,000	2,200,000
Employee stock option plan [Member]
Stock Repurchase				238,473
Remaining Loan Term				16 years 6 months
Percentage of Purchase price common stock				100.00%
Remaining Principal Balance of Debt				$ 2,000,000.0	$ 2,100,000