Allowance for Loan Losses - Performing and Nonperforming Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment [Line Items]
Performing	$ 393,911	$ 407,051
Nonperforming	2
Total	393,913	407,051
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing	368,822	382,720
Total	368,822	382,720
Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing	12,147	10,565
Total	12,147	10,565
Consumer and Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing	12,942	13,766
Nonperforming	2
Total	$ 12,944	$ 13,766