Commitments, Contingencies and Off-Balance-Sheet Risk - Contractual Amounts of Financial Instruments with Off-Balance-Sheet Risk (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	$ 31,827	$ 39,095
Variable Rate	509,712	470,557
Lines of Credit and Construction Loans [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	31,205	38,474
Variable Rate	465,902	427,864
Overdraft Protection [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	7	6
Variable Rate	42,925	41,707
Letters of Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fixed Rate	615	615
Variable Rate	$ 885	$ 986