Loans - Credit exposure (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 1,336,125	$ 1,164,821
Threshold limit to consider loan as nonperforming	90 days
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 251,666	208,717
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans	760,848	625,218
Commercial real estate | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total Loans	123,147	114,258
Commercial real estate | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans	637,701	510,960
Commercial real estate | Real estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans	637,701	510,960
Residential
Financing Receivable, Recorded Investment [Line Items]
Total Loans	319,183	325,855
Residential | Real estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans	209,326	215,104
Residential | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total Loans	109,857	110,751
Consumer
Financing Receivable, Recorded Investment [Line Items]
Total Loans	4,428	5,031
Consumer | Performing
Financing Receivable, Recorded Investment [Line Items]
Total Loans	4,415	5,003
Consumer | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Total Loans	13	28
Pass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans	248,714	208,098
Pass | Commercial real estate | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total Loans	114,502	112,729
Pass | Commercial real estate | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans	625,861	501,081
Pass | Residential | Real estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans	200,405	199,278
Pass | Residential | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total Loans	107,705	108,799
Special Mention | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,763	592
Special Mention | Commercial real estate | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total Loans	7,114	902
Special Mention | Commercial real estate | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans	6,914	4,859
Special Mention | Residential | Real estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans	4,438	10,600
Special Mention | Residential | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,325	1,257
Substandard | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,189	27
Substandard | Commercial real estate | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,531	627
Substandard | Commercial real estate | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans	4,926	5,020
Substandard | Residential | Real estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans	4,483	5,226
Substandard | Residential | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total Loans	827	695
Doubtful | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Doubtful | Commercial real estate | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Doubtful | Commercial real estate | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Doubtful | Residential | Real estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
Doubtful | Residential | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 0	$ 0