LOANS AND ALLOWANCE FOR LOAN LOSSES - Impaired Loans (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
Unpaid Principal Balance [Abstract]
Unpaid principal balance, total	$ 18,523		$ 18,523		$ 15,712
Recorded Investment [Abstract]
Recorded investment, total	16,354		16,354		15,665
Allowance for loan losses allocated	5,766		5,766		8,097
Average Recorded Investment [Abstract]
Average recorded investment, total	16,049	$ 18,645	15,715	$ 14,111
Interest Income, Accrual Method [Abstract]
Interest income, accrual method, total	23	44	50	61
Commercial mortgages: | Construction
Unpaid Principal Balance [Abstract]
With no related allowance, unpaid principal balance	204		204		247
Recorded Investment [Abstract]
With no related allowance, recorded investment	204		204		247
Average Recorded Investment [Abstract]
With no related allowance, average recorded investment	213	270	226	285
Interest Income, Accrual Method [Abstract]
With no related allowance, interest income, accrual method	2	2	6	7
Commercial mortgages: | Commercial mortgages, other
Unpaid Principal Balance [Abstract]
With no related allowance, unpaid principal balance	6,339		6,339		3,501
With related allowance, Unpaid Principal Balance	2,347		2,347		5,093
Recorded Investment [Abstract]
With no related allowance, recorded investment	4,287		4,287		3,503
With related allowance, recorded investment	2,259		2,259		5,094
Allowance for loan losses allocated	184		184		2,097
Average Recorded Investment [Abstract]
With no related allowance, average recorded investment	4,515	3,372	3,938	3,630
With related allowance, average recorded investment	2,229	10,240	3,645	6,881
Interest Income, Accrual Method [Abstract]
With no related allowance, interest income, accrual method	0	3	0	9
With related allowance, interest income, accrual method	8	0	16	0
Residential mortgages
Unpaid Principal Balance [Abstract]
With no related allowance, unpaid principal balance	1,297		1,297		554
Recorded Investment [Abstract]
With no related allowance, recorded investment	1,277		1,277		525
Average Recorded Investment [Abstract]
With no related allowance, average recorded investment	1,224	396	873	396
Interest Income, Accrual Method [Abstract]
With no related allowance, interest income, accrual method	7	36	17	40
Consumer loans: | Home equity lines and loans
Unpaid Principal Balance [Abstract]
With no related allowance, unpaid principal balance	657		657		171
With related allowance, Unpaid Principal Balance	170		170		0
Recorded Investment [Abstract]
With no related allowance, recorded investment	642		642		149
With related allowance, recorded investment	170		170		0
Allowance for loan losses allocated	52		52		0
Average Recorded Investment [Abstract]
With no related allowance, average recorded investment	650	156	399	134
With related allowance, average recorded investment	175	0	88	0
Interest Income, Accrual Method [Abstract]
With no related allowance, interest income, accrual method	2	3	5	4
With related allowance, interest income, accrual method	0	0	0	0
Commercial and industrial | Commercial and agricultural:
Unpaid Principal Balance [Abstract]
With no related allowance, unpaid principal balance	1,391		1,391		133
With related allowance, Unpaid Principal Balance	6,118		6,118		6,013
Recorded Investment [Abstract]
With no related allowance, recorded investment	1,391		1,391		133
With related allowance, recorded investment	6,124		6,124		6,014
Allowance for loan losses allocated	5,530		5,530		$ 6,000
Average Recorded Investment [Abstract]
With no related allowance, average recorded investment	1,239	228	679	277
With related allowance, average recorded investment	5,804	3,983	5,867	2,508
Interest Income, Accrual Method [Abstract]
With no related allowance, interest income, accrual method	2	0	2	1
With related allowance, interest income, accrual method	$ 2	$ 0	$ 4	$ 0