Condensed Financial Statements of Parent Company - Schedule of Condensed Statements of Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income tax expense	$ (451)	$ 601
Net (loss) income	(565)	2,621
First Seacoast Bancorp (Parent) Company
Interest on ESOP loan	110	115
Miscellaneous expense	4	3
Income before income tax expense and equity in undistributed net (loss) income of First Seacoast Bank	106	112
Income tax expense	62
Net income before equity in undistributed net income of First Seacoast Bank	44	112
Equity in undistributed net income of First Seacoast Bank	(609)	2,509
Net (loss) income	$ (565)	$ 2,621