Allowance for loan losses and credit quality Impaired Loans by Class (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020		Jun. 30, 2019		Jun. 30, 2020		Jun. 30, 2019		Dec. 31, 2019
Financing Receivable, Impaired [Line Items]
With an alowance recorded, Recorded Investment	$ 2,279	[1]			$ 2,279	[1]			$ 1,991
With an allowance recorded, Principal Balance	2,370	[1]			2,370	[1]			2,023
Related Allowance	130		$ 52		130		$ 52		196
With no allowance recorded, Recorded Investment	3,233	[1]			3,233	[1]			3,250	[2]
With no allowance recorded, Principal Balance	3,909	[1]			3,909	[1]			3,902	[2]
Total, Recorded Investment	5,512	[1]	3,544	[3]	5,512	[1]	3,544	[3]	5,241	[2]
Total, Principal Balance	6,279	[1]	4,221	[3]	6,279	[1]	4,221	[3]	5,925	[2]
Total, Average Recorded Investment	5,328		3,694		5,298		3,937
Total, Interest Income Recognized	31		51		80		116
Government Guarantees on Impaired Loans	553		613		553		613		587
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
With an alowance recorded, Recorded Investment	213				213				218
With an allowance recorded, Principal Balance	222				222				228
Related Allowance	35		44		35		44		39
With no allowance recorded, Recorded Investment	1,746	[1]			1,746	[1]			1,297	[2]
With no allowance recorded, Principal Balance	2,302	[1]			2,302	[1]			1,832	[2]
Total, Recorded Investment	1,959	[1]	1,617	[3]	1,959	[1]	1,617	[3]	1,515	[2]
Total, Principal Balance	2,524	[1]	2,180	[3]	2,524	[1]	2,180	[3]	2,060	[2]
Total, Average Recorded Investment	1,724		1,669		1,654		1,672
Total, Interest Income Recognized	9		19		28		38
Construction Real Estate [Member]
Financing Receivable, Impaired [Line Items]
With an alowance recorded, Recorded Investment	69				69
With an allowance recorded, Principal Balance	69				69
Related Allowance	2		0		2		0		0
With no allowance recorded, Recorded Investment	149				149				223
With no allowance recorded, Principal Balance	168				168				241
Total, Recorded Investment	218		110		218		110		223
Total, Principal Balance	237		128		237		128		241
Total, Average Recorded Investment	218		112		219		114
Total, Interest Income Recognized	1		1		2		2
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
With an alowance recorded, Recorded Investment	1,987				1,987				1,762
With an allowance recorded, Principal Balance	2,068				2,068				1,783
Related Allowance	86		0		86		0		149
With no allowance recorded, Recorded Investment	1,098	[1]			1,098	[1]			1,442	[2]
With no allowance recorded, Principal Balance	1,196	[1]			1,196	[1]			1,539	[2]
Total, Recorded Investment	3,085	[1]	1,496	[3]	3,085	[1]	1,496	[3]	3,204	[2]
Total, Principal Balance	3,264	[1]	1,590	[3]	3,264	[1]	1,590	[3]	3,322	[2]
Total, Average Recorded Investment	3,121		1,583		3,149		1,814
Total, Interest Income Recognized	16		25		38		65
Commercial [Member]
Financing Receivable, Impaired [Line Items]
With an alowance recorded, Recorded Investment	10	[1]			10	[1]			11
With an allowance recorded, Principal Balance	11	[1]			11	[1]			12
Related Allowance	7		8		7		8		8
With no allowance recorded, Recorded Investment	240	[1]			240	[1]			288	[2]
With no allowance recorded, Principal Balance	243	[1]			243	[1]			290	[2]
Total, Recorded Investment	250	[1]	321	[3]	250	[1]	321	[3]	299	[2]
Total, Principal Balance	254	[1]	323	[3]	254	[1]	323	[3]	$ 302	[2]
Total, Average Recorded Investment	265		330		276		337
Total, Interest Income Recognized	$ 5		$ 6		$ 12		$ 11

[1] Does not reflect government guaranties on impaired loans as of June 30, 2020 totaling $553 thousand.

[2] Does not reflect government guaranties on impaired loans as of December 31, 2019 totaling $587 thousand.

[3] Does not reflect government guaranties on impaired loans as of June 30, 2019 totaling $613 thousand.