LOAN PORTFOLIO AND CREDIT QUALITY - Impaired Loans With and Without Related Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Recorded Investment:
With no related allowance recorded:	$ 22,364	$ 18,122
With an allowance recorded:	2,778	1,065
Total:	25,142	19,187
Unpaid principal balance:
With no related allowance recorded:	22,841	19,027
With an allowance recorded:	2,815	1,065
Total:	25,656	20,092
Related Allowance	400	235
Average Recorded Investment:
With no related allowance recorded:	24,063	17,012
With an allowance recorded:	1,163	2,411
Total:	25,226	19,423	$ 20,817
Interest Income Recognized while Impaired:
With no related allowance recorded:	744	1,201
With an allowance recorded:	21	60
Total:	765	1,261	2,817
Commercial and industrial
Recorded Investment:
With no related allowance recorded:	2,262	470
With an allowance recorded:	2,053	254
Total:	4,315	724
Unpaid principal balance:
With no related allowance recorded:	2,307	553
With an allowance recorded:	2,090	254
Total:	4,397	807
Related Allowance	279	146
Average Recorded Investment:
With no related allowance recorded:	2,512	1,062
With an allowance recorded:	378	736
Total:	2,890	1,798	2,245
Interest Income Recognized while Impaired:
With no related allowance recorded:	141	268
With an allowance recorded:	1	33
Total:	142	301	84
Paycheck Protection Program
Recorded Investment:
With no related allowance recorded:	0
With an allowance recorded:	0
Total:	0
Unpaid principal balance:
With no related allowance recorded:	0
With an allowance recorded:	0
Total:	0
Related Allowance	0
Average Recorded Investment:
With no related allowance recorded:	0
With an allowance recorded:	0
Total:	0
Interest Income Recognized while Impaired:
With no related allowance recorded:	0
With an allowance recorded:	0
Total:	0
Commercial tax-exempt
Recorded Investment:
With no related allowance recorded:	0	0
With an allowance recorded:	0	0
Total:	0	0
Unpaid principal balance:
With no related allowance recorded:	0	0
With an allowance recorded:	0	0
Total:	0	0
Related Allowance	0	0
Average Recorded Investment:
With no related allowance recorded:	302	0
With an allowance recorded:	0	0
Total:	302	0	0
Interest Income Recognized while Impaired:
With no related allowance recorded:	20	0
With an allowance recorded:	0	0
Total:	20	0	0
Commercial real estate
Recorded Investment:
With no related allowance recorded:	5,212	733
With an allowance recorded:	50	0
Total:	5,262	733
Unpaid principal balance:
With no related allowance recorded:	5,384	733
With an allowance recorded:	50	0
Total:	5,434	733
Related Allowance	50	0
Average Recorded Investment:
With no related allowance recorded:	4,818	155
With an allowance recorded:	23	0
Total:	4,841	155	6,089
Interest Income Recognized while Impaired:
With no related allowance recorded:	33	262
With an allowance recorded:	0	0
Total:	33	262	2,249
Construction and land
Recorded Investment:
With no related allowance recorded:	0	0
With an allowance recorded:	0	0
Total:	0	0
Unpaid principal balance:
With no related allowance recorded:	0	0
With an allowance recorded:	0	0
Total:	0	0
Related Allowance	0	0
Average Recorded Investment:
With no related allowance recorded:	0	0
With an allowance recorded:	0	0
Total:	0	0	50
Interest Income Recognized while Impaired:
With no related allowance recorded:	0	0
With an allowance recorded:	0	0
Total:	0	0	16
Residential
Recorded Investment:
With no related allowance recorded:	14,523	15,362
With an allowance recorded:	419	538
Total:	14,942	15,900
Unpaid principal balance:
With no related allowance recorded:	14,783	15,622
With an allowance recorded:	419	538
Total:	15,202	16,160
Related Allowance	54	67
Average Recorded Investment:
With no related allowance recorded:	15,509	13,700
With an allowance recorded:	498	1,130
Total:	16,007	14,830	10,423
Interest Income Recognized while Impaired:
With no related allowance recorded:	534	636
With an allowance recorded:	13	23
Total:	547	659	430
Home equity
Recorded Investment:
With no related allowance recorded:	367	1,557
With an allowance recorded:	256	273
Total:	623	1,830
Unpaid principal balance:
With no related allowance recorded:	367	2,119
With an allowance recorded:	256	273
Total:	623	2,392
Related Allowance	17	22
Average Recorded Investment:
With no related allowance recorded:	922	2,095
With an allowance recorded:	264	545
Total:	1,186	2,640	2,000
Interest Income Recognized while Impaired:
With no related allowance recorded:	16	35
With an allowance recorded:	7	4
Total:	23	39	35
Consumer and other
Recorded Investment:
With no related allowance recorded:	0	0
With an allowance recorded:	0	0
Total:	0	0
Unpaid principal balance:
With no related allowance recorded:	0	0
With an allowance recorded:	0	0
Total:	0	0
Related Allowance	0	0
Average Recorded Investment:
With no related allowance recorded:	0	0
With an allowance recorded:	0	0
Total:	0	0	10
Interest Income Recognized while Impaired:
With no related allowance recorded:	0	0
With an allowance recorded:	0	0
Total:	$ 0	$ 0	$ 3