Allowance for loan losses and credit quality Impaired Loans by Class (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2020		Sep. 30, 2019		Sep. 30, 2020		Sep. 30, 2019		Dec. 31, 2019
Financing Receivable, Impaired [Line Items]
With an alowance recorded, recorded investment	$ 1,870	[1]			$ 1,870	[1]			$ 1,991
With an allowance recorded, principal balance	2,008	[1]			2,008	[1]			2,023
Related Allowance	76		$ 225		76		$ 225		196
With no allowance recorded, recorded investment	3,394	[1]			3,394	[1]			3,250	[2]
With no allowance recorded, principal balance	4,116	[1]			4,116	[1]			3,902	[2]
Total, recorded investment	5,264	[1]	5,385	[3]	5,264	[1]	5,385	[3]	5,241	[2]
Total, principal balance	6,124	[1]	6,074	[3]	6,124	[1]	6,074	[3]	5,925	[2]
Average Recorded Investment	5,388		4,465		5,290		4,299
Interest Income Recognized	50		50		130		166
Government guarantees on impaired loans	535		592		535		592		587
Residential real estate
Financing Receivable, Impaired [Line Items]
With an alowance recorded, recorded investment	211				211				218
With an allowance recorded, principal balance	221				221				228
Related Allowance	33		41		33		41		39
With no allowance recorded, recorded investment	1,594	[1]			1,594	[1]			1,297	[2]
With no allowance recorded, principal balance	2,192	[1]			2,192	[1]			1,832	[2]
Total, recorded investment	1,805	[1]	1,595	[3]	1,805	[1]	1,595	[3]	1,515	[2]
Total, principal balance	2,413	[1]	2,168	[3]	2,413	[1]	2,168	[3]	2,060	[2]
Average Recorded Investment	1,882		1,606		1,692		1,653
Interest Income Recognized	19		17		47		55
Construction real estate
Financing Receivable, Impaired [Line Items]
Related Allowance	0		0		0		0		0
With no allowance recorded, recorded investment	212				212				223
With no allowance recorded, principal balance	233				233				241
Total, recorded investment	212		229		212		229		223
Total, principal balance	233		247		233		247		241
Average Recorded Investment	215		170		218		143
Interest Income Recognized	1		1		3		3
Commercial real estate
Financing Receivable, Impaired [Line Items]
With an alowance recorded, recorded investment	1,650				1,650				1,762
With an allowance recorded, principal balance	1,776				1,776				1,783
Related Allowance	36		176		36		176		149
With no allowance recorded, recorded investment	1,368	[1]			1,368	[1]			1,442	[2]
With no allowance recorded, principal balance	1,469	[1]			1,469	[1]			1,539	[2]
Total, recorded investment	3,018	[1]	3,264	[3]	3,018	[1]	3,264	[3]	3,204	[2]
Total, principal balance	3,245	[1]	3,359	[3]	3,245	[1]	3,359	[3]	3,322	[2]
Average Recorded Investment	3,051		2,380		3,116		2,176
Interest Income Recognized	26		24		64		89
Commercial
Financing Receivable, Impaired [Line Items]
With an alowance recorded, recorded investment	9	[1]			9	[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	220	[1]			220	[1]			288	[2]
With no allowance recorded, principal balance	222	[1]			222	[1]			290	[2]
Total, recorded investment	229	[1]	297	[3]	229	[1]	297	[3]	299	[2]
Total, principal balance	233	[1]	300	[3]	233	[1]	300	[3]	$ 302	[2]
Average Recorded Investment	240		309		264		327
Interest Income Recognized	$ 4		$ 8		$ 16		$ 19

[1] Does not reflect government guaranties on impaired loans as of September 30, 2020 totaling $535 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 September 30, 2019 totaling $592 thousand.