Loans - Past-due Status of Loans by Class (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Schedule of Financing Receivables [Line Items]
All Past Due	$ 7,438	$ 18,676	$ 9,786
Current	1,217,002	1,145,463	1,110,879
Total	1,224,440	1,164,139	1,120,665
90 Days or More & Accruing	3	445	29
30-59 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	2,112	2,944	1,471
60-89 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	2,206	11,948	4,126
90 Days or More Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	3,120	3,784	4,189
Commercial | Real estate
Schedule of Financing Receivables [Line Items]
All Past Due	715	874	1,475
Current	349,399	322,935	305,015
Total	350,114	323,809	306,490
90 Days or More & Accruing	0	0	0
Commercial | Real estate | 30-59 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	137	574	88
Commercial | Real estate | 60-89 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	75	80	0
Commercial | Real estate | 90 Days or More Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	503	220	1,387
Commercial | Construction
Schedule of Financing Receivables [Line Items]
All Past Due	0	0	0
Current	40,308	38,056	33,605
Total	40,308	38,056	33,605
90 Days or More & Accruing	0	0	0
Commercial | Construction | 30-59 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	0	0	0
Commercial | Construction | 60-89 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	0	0	0
Commercial | Construction | 90 Days or More Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	0	0	0
Commercial | Other
Schedule of Financing Receivables [Line Items]
All Past Due	795	7,779	803
Current	183,923	173,749	172,888
Total	184,718	181,528	173,691
90 Days or More & Accruing	0	0	0
Commercial | Other | 30-59 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	459	542	29
Commercial | Other | 60-89 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	42	6,663	259
Commercial | Other | 90 Days or More Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	294	574	515
Municipal
Schedule of Financing Receivables [Line Items]
All Past Due	0	0	0
Current	48,717	33,391	28,695
Total	48,717	33,391	28,695
90 Days or More & Accruing	0	0	0
Municipal | 30-59 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	0	0	0
Municipal | 60-89 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	0	0	0
Municipal | 90 Days or More Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	0	0	0
Residential | Construction
Schedule of Financing Receivables [Line Items]
All Past Due	0	471	99
Current	14,583	17,397	14,957
Total	14,583	17,868	15,056
90 Days or More & Accruing	0	0	0
Residential | Construction | 30-59 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	0	101	99
Residential | Construction | 60-89 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	0	370	0
Residential | Construction | 90 Days or More Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	0	0	0
Residential | Term
Schedule of Financing Receivables [Line Items]
All Past Due	4,275	7,659	5,383
Current	449,313	425,002	421,788
Total	453,588	432,661	427,171
90 Days or More & Accruing	0	436	0
Residential | Term | 30-59 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	531	1,031	533
Residential | Term | 60-89 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	2,014	4,372	3,343
Residential | Term | 90 Days or More Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	1,730	2,256	1,507
Home equity line of credit
Schedule of Financing Receivables [Line Items]
All Past Due	1,528	1,707	1,597
Current	106,138	109,595	108,731
Total	107,666	111,302	110,328
90 Days or More & Accruing	0	0	0
Home equity line of credit | 30-59 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	915	537	440
Home equity line of credit | 60-89 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	38	445	406
Home equity line of credit | 90 Days or More Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	575	725	751
Consumer
Schedule of Financing Receivables [Line Items]
All Past Due	125	186	429
Current	24,621	25,338	25,200
Total	24,746	25,524	25,629
90 Days or More & Accruing	3	9	29
Consumer | 30-59 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	70	159	282
Consumer | 60-89 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	37	18	118
Consumer | 90 Days or More Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	$ 18	$ 9	$ 29