LOANS AND ALLOWANCE FOR LOAN LOSSES - Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Unpaid Principal Balance [Abstract]
Unpaid principal balance, total	$ 9,387		$ 9,387		$ 14,094
Recorded Investment [Abstract]
Recorded investment, total	9,342		9,342		13,926
Allowance for loan losses allocated	1,738		1,738		5,937
Average Recorded Investment [Abstract]
Average recorded investment, total	11,490	$ 13,273	12,303	$ 12,825
Interest Income, Accrual Method [Abstract]
Interest income, accrual method, total	19	51	40	126
Commercial Mortgages | Construction
Unpaid Principal Balance [Abstract]
With no related allowance, Unpaid Principal Balance	336		336		364
Recorded Investment [Abstract]
With no related allowance, Recorded Investment	338		338		365
Average Recorded Investment [Abstract]
With no related allowance, Average Recorded Investment	345	1,555	352	1,130
Interest Income, Accrual Method [Abstract]
With no related allowance, Interest Income, Accrual Method	3	3	6	6
Commercial Mortgages | Commercial mortgages, other
Unpaid Principal Balance [Abstract]
With no related allowance, Unpaid Principal Balance	4,366		4,366		4,135
With related allowance, Unpaid Principal Balance	2,173		2,173		2,989
Recorded Investment [Abstract]
With no related allowance, Recorded Investment	4,370		4,370		4,138
With related allowance, Recorded Investment	2,139		2,139		2,799
Allowance for loan losses allocated	453		453		802
Average Recorded Investment [Abstract]
With no related allowance, Average Recorded Investment	4,290	5,879	4,240	6,538
With related allowance, Average Recorded Investment	2,467	4,461	2,578	3,723
Interest Income, Accrual Method [Abstract]
With no related allowance, Interest Income, Accrual Method	5	32	10	90
With related allowance, Interest Income, Accrual Method	1	4	3	7
Residential mortgages
Unpaid Principal Balance [Abstract]
With no related allowance, Unpaid Principal Balance	439		439		450
Recorded Investment [Abstract]
With no related allowance, Recorded Investment	417		417		427
Average Recorded Investment [Abstract]
With no related allowance, Average Recorded Investment	421	417	423	410
Interest Income, Accrual Method [Abstract]
With no related allowance, Interest Income, Accrual Method	2	2	4	4
Consumer loans: | Home equity lines and loans
Unpaid Principal Balance [Abstract]
With no related allowance, Unpaid Principal Balance	60		60		64
Recorded Investment [Abstract]
With no related allowance, Recorded Investment	61		61		64
Average Recorded Investment [Abstract]
With no related allowance, Average Recorded Investment	61	71	62	79
With related allowance, Average Recorded Investment	0	180	0	240
Interest Income, Accrual Method [Abstract]
With no related allowance, Interest Income, Accrual Method	1	1	2	1
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	643		643		861
With related allowance, Unpaid Principal Balance	1,370		1,370		5,231
Recorded Investment [Abstract]
With no related allowance, Recorded Investment	647		647		867
With related allowance, Recorded Investment	1,370		1,370		5,266
Allowance for loan losses allocated	1,285		1,285		$ 5,135
Average Recorded Investment [Abstract]
With no related allowance, Average Recorded Investment	710	626	762	649
With related allowance, Average Recorded Investment	3,196	84	3,886	56
Interest Income, Accrual Method [Abstract]
With no related allowance, Interest Income, Accrual Method	7	8	15	17
With related allowance, Interest Income, Accrual Method	$ 0	$ 1	$ 0	$ 1