Allowance for Loan Losses - Performing and Nonperforming Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment [Line Items]
Performing	$ 369,770	$ 382,911
Total	369,770	382,911
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing	343,970	354,987
Total	343,970	354,987
Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing	14,688	15,948
Total	14,688	15,948
Consumer and Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing	11,112	11,976
Total	$ 11,112	$ 11,976