Loan Portfolio and Credit Quality Impaired Loans With and Without Related Allowance (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Recorded Investment
With no related allowance recorded:	$ 24,574	$ 15,315	$ 18,122
With an allowance recorded:	1,075	1,899	1,065
Total:	25,649	17,214	19,187
Unpaid Principal Balance
With no related allowance recorded:	25,504	17,005	19,027
With an allowance recorded:	1,082	1,950	1,065
Total:	26,586	18,955	20,092
Related Allowance	259	299	235
Average Recorded Investment
With no related allowance recorded:	20,207	13,922	17,012
With an allowance recorded:	1,087	3,564	2,411
Total:	21,294	17,486	19,423
Interest Income Recognized while Impaired
With no related allowance recorded:	135	408	1,201
With an allowance recorded:	6	23	60
Total:	141	431	1,261
Commercial and industrial
Recorded Investment
With no related allowance recorded:	555	862	470
With an allowance recorded:	273	1,302	254
Total:	828	2,164	724
Unpaid Principal Balance
With no related allowance recorded:	632	1,730	553
With an allowance recorded:	280	1,353	254
Total:	912	3,083	807
Related Allowance	175	231	146
Average Recorded Investment
With no related allowance recorded:	667	1,021	1,062
With an allowance recorded:	281	1,542	736
Total:	948	2,563	1,798
Interest Income Recognized while Impaired
With no related allowance recorded:	6	15	268
With an allowance recorded:	0	16	33
Total:	6	31	301
Commercial tax-exempt
Recorded Investment
With no related allowance recorded:	0	0	0
With an allowance recorded:	0	0	0
Total:	0	0	0
Unpaid Principal Balance
With no related allowance recorded:	0	0	0
With an allowance recorded:	0	0	0
Total:	0	0	0
Related Allowance	0	0	0
Average Recorded Investment
With no related allowance recorded:	0	0	0
With an allowance recorded:	0	0	0
Total:	0	0	0
Interest Income Recognized while Impaired
With no related allowance recorded:	0	0	0
With an allowance recorded:	0	0	0
Total:	0	0	0
Commercial real estate
Recorded Investment
With no related allowance recorded:	6,119	0	733
With an allowance recorded:	0	0	0
Total:	6,119	0	733
Unpaid Principal Balance
With no related allowance recorded:	6,151	0	733
With an allowance recorded:	0	0	0
Total:	6,151	0	733
Related Allowance	0	0	0
Average Recorded Investment
With no related allowance recorded:	2,403	136	155
With an allowance recorded:	0	0	0
Total:	2,403	136	155
Interest Income Recognized while Impaired
With no related allowance recorded:	9	256	262
With an allowance recorded:	0	0	0
Total:	9	256	262
Construction and land
Recorded Investment
With no related allowance recorded:	0	0	0
With an allowance recorded:	0	0	0
Total:	0	0	0
Unpaid Principal Balance
With no related allowance recorded:	0	0	0
With an allowance recorded:	0	0	0
Total:	0	0	0
Related Allowance	0	0	0
Average Recorded Investment
With no related allowance recorded:	0	0	0
With an allowance recorded:	0	0	0
Total:	0	0	0
Interest Income Recognized while Impaired
With no related allowance recorded:	0	0	0
With an allowance recorded:	0	0	0
Total:	0	0	0
Residential
Recorded Investment
With no related allowance recorded:	16,352	12,306	15,362
With an allowance recorded:	532	597	538
Total:	16,884	12,903	15,900
Unpaid Principal Balance
With no related allowance recorded:	16,612	12,566	15,622
With an allowance recorded:	532	597	538
Total:	17,144	13,163	16,160
Related Allowance	64	68	67
Average Recorded Investment
With no related allowance recorded:	15,587	11,056	13,700
With an allowance recorded:	535	732	1,130
Total:	16,122	11,788	14,830
Interest Income Recognized while Impaired
With no related allowance recorded:	117	137	636
With an allowance recorded:	4	7	23
Total:	121	144	659
Home equity
Recorded Investment
With no related allowance recorded:	1,548	2,147	1,557
With an allowance recorded:	270	0	273
Total:	1,818	2,147	1,830
Unpaid Principal Balance
With no related allowance recorded:	2,109	2,709	2,119
With an allowance recorded:	270	0	273
Total:	2,379	2,709	2,392
Related Allowance	20	0	22
Average Recorded Investment
With no related allowance recorded:	1,550	1,709	2,095
With an allowance recorded:	271	1,290	545
Total:	1,821	2,999	2,640
Interest Income Recognized while Impaired
With no related allowance recorded:	3	0	35
With an allowance recorded:	2	0	4
Total:	5	0	39
Consumer and other
Recorded Investment
With no related allowance recorded:	0	0	0
With an allowance recorded:	0	0	0
Total:	0	0	0
Unpaid Principal Balance
With no related allowance recorded:	0	0	0
With an allowance recorded:	0	0	0
Total:	0	0	0
Related Allowance	0	0	0
Average Recorded Investment
With no related allowance recorded:	0	0	0
With an allowance recorded:	0	0	0
Total:	0	0	0
Interest Income Recognized while Impaired
With no related allowance recorded:	0	0	0
With an allowance recorded:	0	0	0
Total:	$ 0	$ 0	$ 0