Loans - Summary of Recorded Investment of Purchased Impaired Loans (Detail) - PCI Loans - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	$ 39	$ 390
90 Days or More Past Due and Still Accruing	162	16
Nonaccrual	0	0
Total Past Due and Nonaccrual	201	406
Current	3,989	4,464
Total PCI Loans	4,190	4,870
Residential first mortgages
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	39	239
90 Days or More Past Due and Still Accruing	13	16
Nonaccrual	0	0
Total Past Due and Nonaccrual	52	255
Current	2,381	2,836
Total PCI Loans	2,433	3,091
Commercial mortgages (non-owner occupied)
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due		126
90 Days or More Past Due and Still Accruing	128
Nonaccrual	0	0
Total Past Due and Nonaccrual	128	126
Total PCI Loans	128	126
Construction, land and land development
Financing Receivable, Impaired [Line Items]
Nonaccrual	0	0
Current	1,368	1,357
Total PCI Loans	1,368	1,357
Commercial mortgages (owner occupied)
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due		25
90 Days or More Past Due and Still Accruing	21
Nonaccrual	0	0
Total Past Due and Nonaccrual	21	25
Current	203	229
Total PCI Loans	224	254
Residential revolving and junior mortgages
Financing Receivable, Impaired [Line Items]
Nonaccrual	0	0
Commercial and industrial
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	0	0
90 Days or More Past Due and Still Accruing	0	0
Nonaccrual	0	0
Total Past Due and Nonaccrual	0	0
Current	0	0
Total PCI Loans	0	0
Paycheck Protection Program
Financing Receivable, Impaired [Line Items]
Nonaccrual	0
Consumer
Financing Receivable, Impaired [Line Items]
Nonaccrual	0	0
Current	37	42
Total PCI Loans	$ 37	$ 42