Loans - Schedule of Loans Not Rated by Class of Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Modifications [Line Items]
Loans not rated by class of loans	$ 194,785	$ 204,914
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Loans not rated by class of loans	1,475	1,924
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Loans not rated by class of loans	1,412	1,773
Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Loans not rated by class of loans	168,280	176,867
Construction & Land Development [Member]
Financing Receivable, Modifications [Line Items]
Loans not rated by class of loans	7,272	6,539
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Loans not rated by class of loans	16,346	17,811
Performing [Member]
Financing Receivable, Modifications [Line Items]
Loans not rated by class of loans	194,225	204,312
Performing [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Loans not rated by class of loans	1,475	1,924
Performing [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Loans not rated by class of loans	1,412	1,773
Performing [Member] | Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Loans not rated by class of loans	167,738	176,278
Performing [Member] | Construction & Land Development [Member]
Financing Receivable, Modifications [Line Items]
Loans not rated by class of loans	7,272	6,539
Performing [Member] | Consumer [Member]
Financing Receivable, Modifications [Line Items]
Loans not rated by class of loans	16,328	17,798
Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Loans not rated by class of loans	560	602
Nonperforming [Member] | Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Loans not rated by class of loans	542	589
Nonperforming [Member] | Consumer [Member]
Financing Receivable, Modifications [Line Items]
Loans not rated by class of loans	$ 18	$ 13