Loans - Summary of Recorded Investment of Purchased Impaired Loans (Detail) - PCI Loans - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	$ 306	$ 115
90 Days or More Past Due and Still Accruing	47	111
Nonaccrual	0	0
Total Past Due and Nonaccrual	353	226
Current	4,917	5,097
Total PCI Loans	5,270	5,323
Construction, land and land development
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	23	23
Nonaccrual	0	0
Total Past Due and Nonaccrual	23	23
Current	1,348	1,355
Total PCI Loans	1,371	1,378
Commercial mortgages (non-owner occupied)
Financing Receivable, Impaired [Line Items]
Nonaccrual	0	0
Current	135	142
Total PCI Loans	135	142
Commercial mortgages (owner occupied)
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	26
90 Days or More Past Due and Still Accruing	23	56
Nonaccrual	0	0
Total Past Due and Nonaccrual	49	56
Current	232	237
Total PCI Loans	281	293
Residential first mortgages
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	257	92
90 Days or More Past Due and Still Accruing	24	55
Nonaccrual	0	0
Total Past Due and Nonaccrual	281	147
Current	3,154	3,317
Total PCI Loans	3,435	3,464
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
Consumer
Financing Receivable, Impaired [Line Items]
Nonaccrual	0	0
Current	48	46
Total PCI Loans	$ 48	$ 46