Loans - Summary of Recorded investment of purchased impaired loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	$ 1,262	$ 2,679
90 Days or More Past Due and Still Accruing	0	0
Nonaccruals	5,362	5,300
Total Past Due and Nonaccruals	6,624	7,979
Current	643,002	377,030
Total loans	649,626	385,009
Construction, Land and Land Development
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	93
90 Days or More Past Due and Still Accruing	0	0
Nonaccruals	542	623
Total Past Due and Nonaccruals	635	623
Current	57,256	39,195
Total loans	57,891	39,818
Commercial Mortgages (Non-Owner Occupied)
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	454
90 Days or More Past Due and Still Accruing	0	0
Total Past Due and Nonaccruals	454
Current	79,786	35,343
Total loans	80,240	35,343
Commercial Mortgages (Owner Occupied)
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due		188
90 Days or More Past Due and Still Accruing	0	0
Nonaccruals	1,747	2,270
Total Past Due and Nonaccruals	1,747	2,458
Current	72,234	39,367
Total loans	73,981	41,825
Residential First Mortgages
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	236	1,546
90 Days or More Past Due and Still Accruing	0	0
Nonaccruals	1,941	2,155
Total Past Due and Nonaccruals	2,177	3,701
Current	257,897	190,306
Total loans	260,074	194,007
Residential Revolving and Junior Mortgages
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	43	480
90 Days or More Past Due and Still Accruing	0	0
Nonaccruals	956	160
Total Past Due and Nonaccruals	999	640
Current	48,307	25,785
Total loans	49,306	26,425
Consumer and Other Loans
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	436
90 Days or More Past Due and Still Accruing	0	0
Nonaccruals	66
Total Past Due and Nonaccruals	502
Current	40,727	3,544
Total loans	41,229	$ 3,544
Impaired Financing Receivable
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	29
90 Days or More Past Due and Still Accruing	408
Nonaccruals	0
Total Past Due and Nonaccruals	437
Current	5,553
Total loans	5,990
Impaired Financing Receivable | Construction, Land and Land Development
Financing Receivable, Impaired [Line Items]
Nonaccruals	0
Current	1,421
Total loans	1,421
Impaired Financing Receivable | Commercial Mortgages (Non-Owner Occupied)
Financing Receivable, Impaired [Line Items]
Nonaccruals	0
Current	187
Total loans	187
Impaired Financing Receivable | Commercial Mortgages (Owner Occupied)
Financing Receivable, Impaired [Line Items]
90 Days or More Past Due and Still Accruing	182
Nonaccruals	0
Total Past Due and Nonaccruals	182
Current	173
Total loans	355
Impaired Financing Receivable | Residential First Mortgages
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	24
90 Days or More Past Due and Still Accruing	206
Nonaccruals	0
Total Past Due and Nonaccruals	230
Current	3,665
Total loans	3,895
Impaired Financing Receivable | Residential Revolving and Junior Mortgages
Financing Receivable, Impaired [Line Items]
90 Days or More Past Due and Still Accruing	20
Nonaccruals	0
Total Past Due and Nonaccruals	20
Current	34
Total loans	54
Impaired Financing Receivable | Consumer and Other Loans
Financing Receivable, Impaired [Line Items]
30-89 Days Past Due	5
Nonaccruals	0
Total Past Due and Nonaccruals	5
Current	73
Total loans	$ 78