Recent Accounting Pronouncements - Additional Information (Details)	12 Months Ended
Dec. 31, 2021
Accounting Policies [Abstract]
Emerging Growth of Company Status	(i) the last day of the fiscal year of the Company during which it had total annual gross revenues of $1.07 billion (as adjusted for inflation) or more; (ii) the last day of the fiscal year of the Company following the fifth anniversary of the effective date of the Company’s initial public offering (which will be December 31, 2024 for First Seacoast Bancorp); (iii) the date on which the Company has, during the previous three-year period, issued more than $1.0 billion in non-convertible debt; or (iv) the date on which the Company is deemed to be a “large accelerated filer” under Securities and Exchange Commission regulations (generally, at least $700 million of voting and non-voting equity held by non-affiliates).

Recent Accounting Pronouncements - Additional Information (Details)

12 Months Ended

Dec. 31, 2021

(i) the last day of the fiscal year of the Company during which it had total annual gross revenues of $1.07 billion (as adjusted for inflation) or more; (ii) the last day of the fiscal year of the Company following the fifth anniversary of the effective date of the Company’s initial public offering (which will be December 31, 2024 for First Seacoast Bancorp); (iii) the date on which the Company has, during the previous three-year period, issued more than $1.0 billion in non-convertible debt; or (iv) the date on which the Company is deemed to be a “large accelerated filer” under Securities and Exchange Commission regulations (generally, at least $700 million of voting and non-voting equity held by non-affiliates).