Condensed Financial Statements of Parent Company - Schedule of Condensed Statements of Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Net income	$ 2,621	$ 1,079
First Seacoast Bancorp (Parent) Company
Interest on ESOP loan	115	119
Miscellaneous expense	3	2
Net income before equity in undistributed net income of First Seacoast Bank	112	117
Equity in undistributed net income of First Seacoast Bank	2,509	962
Net income	$ 2,621	$ 1,079