Allowance for Loan Losses (the Allowance) - Roll-forward of allowance by portfolio segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Roll-Forward of Allowance for Loan and Lease Losses by Portfolio Segment
Balance at beginning of period	$ 9,513	$ 8,053
Recoveries	33	104
Provision	1,552	219
Balance at end of period	11,098	8,376
Commercial mortgage
Roll-Forward of Allowance for Loan and Lease Losses by Portfolio Segment
Balance at beginning of period	3,426	3,209
Recoveries		3
Provision	686	(49)
Balance at end of period	4,112	3,163
Home equity lines and loans
Roll-Forward of Allowance for Loan and Lease Losses by Portfolio Segment
Balance at beginning of period	342	323
Recoveries	1	3
Provision	141	15
Balance at end of period	484	341
Residential mortgage
Roll-Forward of Allowance for Loan and Lease Losses by Portfolio Segment
Balance at beginning of period	179	191
Recoveries	2
Provision	38	21
Balance at end of period	219	212
Construction
Roll-Forward of Allowance for Loan and Lease Losses by Portfolio Segment
Balance at beginning of period	2,362	1,627
Provision	19	175
Balance at end of period	2,381	1,802
Commercial and industrial
Roll-Forward of Allowance for Loan and Lease Losses by Portfolio Segment
Balance at beginning of period	2,684	2,612
Recoveries	29	97
Provision	456	51
Balance at end of period	3,169	2,760
Small Business Loans
Roll-Forward of Allowance for Loan and Lease Losses by Portfolio Segment
Balance at beginning of period	509	78
Provision	216	8
Balance at end of period	725	86
Consumer
Roll-Forward of Allowance for Loan and Lease Losses by Portfolio Segment
Balance at beginning of period	6	3
Recoveries	1	1
Provision	(3)
Balance at end of period	4	4
Leases
Roll-Forward of Allowance for Loan and Lease Losses by Portfolio Segment
Balance at beginning of period	5	10
Provision	(1)	(2)
Balance at end of period	$ 4	$ 8