Federal Home Loan Bank Advances - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Total borrowings excluding for fair value related to acquisition	$ 18,026,000	$ 25,500,000
Total borrowings, fair value related to acquisition	164,000	700
Unsecured borrowings through correspondent banks	148,100,000	148,100,000
Unpledged securities which could be sold or used as collateral	206,700,000	116,300,000
Additional borrowings available from the Federal Home Loan Bank based on current pledging	7,400,000	1,600,000
Mortgage Loans at Cost [Member]
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Advances, secured by mortgage loans	$ 38,000,000.0	$ 42,100,000