Allowance for loan losses and credit quality Impaired Loans by Class (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2019		Sep. 30, 2018		Sep. 30, 2019		Sep. 30, 2018		Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
With an alowance recorded, Recorded Investment	$ 2,021				$ 2,021				$ 433
With an allowance recorded, Principal Balance	2,032				2,032				444
Related Allowance	225		$ 58		225		$ 58		66
With no allowance recorded, Recorded Investment	3,364	[1]			3,364	[1]			3,992	[2]
With no allowance recorded, Principal Balance	4,042	[1]			4,042	[1]			4,688	[2]
Total, Recorded Investment	5,385	[1]	4,454	[3]	5,385	[1]	4,454	[3]	4,425	[2]
Total, Principal Balance	6,074	[1]	5,122	[3]	6,074	[1]	5,122	[3]	5,132	[2]
Total, Average Recorded Investment	4,465		4,232		4,299		3,755
Total, Interest Income Recognized	50		48		166		124
Government Guarantees on Impaired Loans	592		656		592		656		641
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
With an alowance recorded, Recorded Investment	221				221				228
With an allowance recorded, Principal Balance	231				231				238
Related Allowance	41		49		41		49		47
With no allowance recorded, Recorded Investment	1,374	[1]			1,374	[1]			1,450	[2]
With no allowance recorded, Principal Balance	1,937	[1]			1,937	[1]			2,039	[2]
Total, Recorded Investment	1,595	[1]	1,688	[3]	1,595	[1]	1,688	[3]	1,678	[2]
Total, Principal Balance	2,168	[1]	2,268	[3]	2,168	[1]	2,268	[3]	2,277	[2]
Total, Average Recorded Investment	1,606		1,743		1,653		1,749
Total, Interest Income Recognized	17		17		55		46
Construction Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Related Allowance	0		0		0		0		0
With no allowance recorded, Recorded Investment	229				229				119
With no allowance recorded, Principal Balance	247				247				135
Total, Recorded Investment	229		78		229		78		119
Total, Principal Balance	247		78		247		78		135
Total, Average Recorded Investment	170		79		143		80
Total, Interest Income Recognized	1		1		3		3
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
With an alowance recorded, Recorded Investment	1,789				1,789				193
With an allowance recorded, Principal Balance	1,789				1,789				193
Related Allowance	176		9		176		9		9
With no allowance recorded, Recorded Investment	1,475	[1]			1,475	[1]			2,083	[2]
With no allowance recorded, Principal Balance	1,570	[1]			1,570	[1]			2,174	[2]
Total, Recorded Investment	3,264	[1]	2,318	[3]	3,264	[1]	2,318	[3]	2,276	[2]
Total, Principal Balance	3,359	[1]	2,406	[3]	3,359	[1]	2,406	[3]	2,367	[2]
Total, Average Recorded Investment	2,380		2,045		2,176		1,555
Total, Interest Income Recognized	24		21		89		52
Commercial [Member]
Financing Receivable, Impaired [Line Items]
With an alowance recorded, Recorded Investment	11				11				12
With an allowance recorded, Principal Balance	12				12				13
Related Allowance	8		0		8		0		10
With no allowance recorded, Recorded Investment	286	[1]			286	[1]			340	[2]
With no allowance recorded, Principal Balance	288	[1]			288	[1]			340	[2]
Total, Recorded Investment	297	[1]	370	[3]	297	[1]	370	[3]	352	[2]
Total, Principal Balance	300	[1]	370	[3]	300	[1]	370	[3]	$ 353	[2]
Total, Average Recorded Investment	309		365		327		371
Total, Interest Income Recognized	$ 8		$ 9		$ 19		$ 23

[1] Does not reflect government guaranties on impaired loans as of September 30, 2019 totaling $592 thousand.

[2] Does not reflect government guaranties on impaired loans as of December 31, 2018 totaling $641 thousand.

[3] Does not reflect government guaranties on impaired loans as of September 30, 2018 totaling $656 thousand.