Loans - Past-due Status of Loans by Class (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Schedule of Financing Receivables [Line Items]
All Past Due	$ 15,867	$ 18,676	$ 10,412
Current	1,172,135	1,145,463	1,079,323
Total	1,188,002	1,164,139	1,089,735
90 Days or More & Accruing	137	445	11
30-59 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	11,940	2,944	4,636
60-89 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	860	11,948	1,127
90 Days or More Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	3,067	3,784	4,649
Commercial | Real estate
Schedule of Financing Receivables [Line Items]
All Past Due	1,182	874	2,737
Current	338,124	322,935	301,926
Total	339,306	323,809	304,663
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	963	574	142
Commercial | Real estate | 60-89 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	17	80	772
Commercial | Real estate | 90 Days or More Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	202	220	1,823
Commercial | Construction
Schedule of Financing Receivables [Line Items]
All Past Due	347	0	20
Current	43,466	38,056	28,755
Total	43,813	38,056	28,775
90 Days or More & Accruing	0	0	0
Commercial | Construction | 30-59 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	347	0	20
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	7,233	7,779	792
Current	170,550	173,749	157,715
Total	177,783	181,528	158,507
90 Days or More & Accruing	0	0	0
Commercial | Other | 30-59 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	6,887	542	199
Commercial | Other | 60-89 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	52	6,663	154
Commercial | Other | 90 Days or More Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	294	574	439
Municipal
Schedule of Financing Receivables [Line Items]
All Past Due	0	0	0
Current	35,463	33,391	28,327
Total	35,463	33,391	28,327
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	0
Current	15,847	17,397	13,717
Total	15,847	17,868	13,717
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	0
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	5,400	7,659	5,158
Current	434,584	425,002	416,044
Total	439,984	432,661	421,202
90 Days or More & Accruing	0	436	0
Residential | Term | 30-59 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	3,175	1,031	3,555
Residential | Term | 60-89 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	345	4,372	0
Residential | Term | 90 Days or More Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	1,880	2,256	1,603
Home equity line of credit
Schedule of Financing Receivables [Line Items]
All Past Due	1,551	1,707	1,332
Current	108,747	109,595	108,684
Total	110,298	111,302	110,016
90 Days or More & Accruing	126	0	0
Home equity line of credit | 30-59 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	449	537	392
Home equity line of credit | 60-89 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	438	445	167
Home equity line of credit | 90 Days or More Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	664	725	773
Consumer
Schedule of Financing Receivables [Line Items]
All Past Due	154	186	373
Current	25,354	25,338	24,155
Total	25,508	25,524	24,528
90 Days or More & Accruing	11	9	11
Consumer | 30-59 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	119	159	328
Consumer | 60-89 Days Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	8	18	34
Consumer | 90 Days or More Past Due
Schedule of Financing Receivables [Line Items]
All Past Due	$ 27	$ 9	$ 11