Loans - Summary of Recorded Investment of Purchased Impaired Loans (Detail) - PCI Loans - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	$ 144	$ 510
90 Days or More Past Due and Still Accruing	87	165
Nonaccruals	0	0
Total Past Due and Nonaccruals	231	675
Current	5,407	5,150
Total PCI Loans	5,638	5,825
Construction, Land and Land Development
Financing Receivable, Impaired [Line Items]
Nonaccruals	0	0
Current	1,390	1,405
Total PCI Loans	1,390	1,405
Commercial Mortgages (Non-Owner Occupied)
Financing Receivable, Impaired [Line Items]
Nonaccruals	0	0
Current	156	171
Total PCI Loans	156	171
Commercial Mortgages (Owner Occupied)
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	121	161
Nonaccruals	0	0
Total Past Due and Nonaccruals	121	161
Current	182	160
Total PCI Loans	303	321
Residential First Mortgages
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	23	349
90 Days or More Past Due and Still Accruing	65	141
Nonaccruals	0	0
Total Past Due and Nonaccruals	88	490
Current	3,599	3,320
Total PCI Loans	3,687	3,810
Residential Revolving and Junior Mortgages
Financing Receivable, Impaired [Line Items]
90 Days or More Past Due and Still Accruing	19	20
Nonaccruals	0	0
Total Past Due and Nonaccruals	19	20
Current	23	29
Total PCI Loans	42	49
Consumer
Financing Receivable, Impaired [Line Items]
90 Days or More Past Due and Still Accruing	3	4
Nonaccruals	0	0
Total Past Due and Nonaccruals	3	4
Current	57	65
Total PCI Loans	$ 60	$ 69