Loans - Summary of Recorded Investment of Purchased Impaired Loans (Detail) - PCI Loans - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	$ 115	$ 510
90 Days or More Past Due and Still Accruing	111	165
Nonaccruals	0	0
Total Past Due and Nonaccruals	226	675
Current	5,097	5,150
Total PCI Loans	5,323	5,825
Construction, land and land development
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	23
Nonaccruals	0	0
Total Past Due and Nonaccruals	23
Current	1,355	1,405
Total PCI Loans	1,378	1,405
Commercial mortgages (non-owner occupied)
Financing Receivable, Impaired [Line Items]
Nonaccruals	0	0
Current	142	171
Total PCI Loans	142	171
Commercial mortgages (owner occupied)
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due		161
90 Days or More Past Due and Still Accruing	56
Nonaccruals	0	0
Total Past Due and Nonaccruals	56	161
Current	237	160
Total PCI Loans	293	321
Residential first mortgages
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	92	349
90 Days or More Past Due and Still Accruing	55	141
Nonaccruals	0	0
Total Past Due and Nonaccruals	147	490
Current	3,317	3,320
Total PCI Loans	3,464	3,810
Residential revolving and junior mortgages
Financing Receivable, Impaired [Line Items]
90 Days or More Past Due and Still Accruing		20
Nonaccruals	0	0
Total Past Due and Nonaccruals		20
Current		29
Total PCI Loans		49
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
Nonaccruals	0	0
Total Past Due and Nonaccruals	0	0
Current	0	0
Total PCI Loans	0	0
Consumer
Financing Receivable, Impaired [Line Items]
90 Days or More Past Due and Still Accruing		4
Nonaccruals	0	0
Total Past Due and Nonaccruals		4
Current	46	65
Total PCI Loans	$ 46	$ 69