Allowance for Loan Losses and Reserve for Unfunded Lending Commitments (Details) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Mar. 31, 2018		Mar. 31, 2017	Dec. 31, 2017		Mar. 31, 2018	Dec. 31, 2017
Allowance for Loan Losses
Balance, beginning of period	$ 13,603	[1]	$ 12,801	$ 12,801
Provision for loan losses	(44)		300	1,016
Charge-offs	(44)		(49)	(690)
Recoveries	60		56	476
Balance, end of period	13,575		13,108	13,603	[1]
Reserve for Unfunded Lending Commitments
Balance, beginning of period	206		203	203
Provision for unfunded commitments	5		3	3
Charge-offs	0		0	0
Balance, end of period	211		206	206
Allowance for Loan Losses
Individually evaluated for impairment						$ 160	$ 167
Collectively evaluated for impairment						13,174	13,151
Total	13,603	[1]	12,801	12,801		13,575	13,603	[1]
Loans
Individually evaluated for impairment						2,462	3,217
Collectively evaluated for impairment						1,296,725	1,309,478
Total Loans						1,321,221	1,336,125	[1]
Acquired impaired loans
Allowance for Loan Losses
Balance, beginning of period	285
Balance, end of period	241			285
Allowance for Loan Losses
Total	285			285		241	285
Loans
Total Loans						22,034	23,430
Commercial
Allowance for Loan Losses
Balance, beginning of period	2,413		2,095	2,095
Provision for loan losses	254			377
Charge-offs	0			(282)
Recoveries	10			223
Balance, end of period	2,677			2,413
Allowance for Loan Losses
Individually evaluated for impairment						60	154
Collectively evaluated for impairment						2,617	2,259
Total	2,413		2,095	2,095		2,677	2,413
Loans
Individually evaluated for impairment						122	206
Collectively evaluated for impairment						283,823	251,185
Total Loans						284,257	251,666
Commercial | Acquired impaired loans
Allowance for Loan Losses
Balance, beginning of period	0
Balance, end of period	0			0
Allowance for Loan Losses
Total	0			0		0	0
Loans
Total Loans						312	275
Commercial Real Estate
Allowance for Loan Losses
Balance, beginning of period	8,321		7,355	7,355
Provision for loan losses	(400)			999
Charge-offs	(11)			(93)
Recoveries	1			60
Balance, end of period	7,911			8,321
Allowance for Loan Losses
Individually evaluated for impairment						0	0
Collectively evaluated for impairment						7,868	8,203
Total	8,321		7,355	7,355		7,911	8,321
Loans
Individually evaluated for impairment						593	862
Collectively evaluated for impairment						705,704	747,819
Total Loans						717,195	760,848
Commercial Real Estate | Acquired impaired loans
Allowance for Loan Losses
Balance, beginning of period	118
Balance, end of period	43			118
Allowance for Loan Losses
Total	118			118		43	118
Loans
Total Loans						10,898	12,167
Residential Real Estate
Allowance for Loan Losses
Balance, beginning of period	2,825		3,303	3,303
Provision for loan losses	97			(391)
Charge-offs	0			(172)
Recoveries	20			85
Balance, end of period	2,942			2,825
Allowance for Loan Losses
Individually evaluated for impairment						100	13
Collectively evaluated for impairment						2,644	2,645
Total	2,825		3,303	3,303		2,942	2,825
Loans
Individually evaluated for impairment						1,743	2,144
Collectively evaluated for impairment						302,728	306,066
Total Loans						315,280	319,183
Residential Real Estate | Acquired impaired loans
Allowance for Loan Losses
Balance, beginning of period	167
Balance, end of period	198			167
Allowance for Loan Losses
Total	167			167		198	167
Loans
Total Loans						10,809	10,973
Consumer
Allowance for Loan Losses
Balance, beginning of period	44		48	48
Provision for loan losses	5			31
Charge-offs	(33)			(143)
Recoveries	29			108
Balance, end of period	45			44
Allowance for Loan Losses
Individually evaluated for impairment						0	0
Collectively evaluated for impairment						45	44
Total	44		$ 48	48		45	44
Loans
Individually evaluated for impairment						4	5
Collectively evaluated for impairment						4,470	4,408
Total Loans						4,489	4,428
Consumer | Acquired impaired loans
Allowance for Loan Losses
Balance, beginning of period	0
Balance, end of period	0			0
Allowance for Loan Losses
Total	$ 0			$ 0		0	0
Loans
Total Loans						$ 15	$ 15

[1] Derived from audited consolidated financial statements.