LOANS AND ALLOWANCE FOR LOAN LOSSES - Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Unpaid Principal Balance [Abstract]
Unpaid principal balance, total	$ 13,842		$ 14,094
Recorded Investment [Abstract]
Recorded investment, total	13,640		13,926
Allowance for loan losses allocated	5,681		5,937
Average Recorded Investment [Abstract]
Average recorded investment, total	13,784	$ 12,684
Interest Income, Accrual Method [Abstract]
Interest income, accrual method, total	21	75
Commercial Mortgages | Construction
Unpaid Principal Balance [Abstract]
With no related allowance, Unpaid Principal Balance	351		364
Recorded Investment [Abstract]
With no related allowance, Recorded Investment	352		365
Average Recorded Investment [Abstract]
With no related allowance, Average Recorded Investment	359	919
Interest Income, Accrual Method [Abstract]
With no related allowance, Interest Income, Accrual Method	3	3
Commercial Mortgages | Commercial mortgages, other
Unpaid Principal Balance [Abstract]
With no related allowance, Unpaid Principal Balance	4,210		4,135
With related allowance, Unpaid Principal Balance	2,984		2,989
Recorded Investment [Abstract]
With no related allowance, Recorded Investment	4,212		4,138
With related allowance, Recorded Investment	2,795		2,799
Allowance for loan losses allocated	771		802
Average Recorded Investment [Abstract]
With no related allowance, Average Recorded Investment	4,175	7,000
With related allowance, Average Recorded Investment	2,797	3,257
Interest Income, Accrual Method [Abstract]
With no related allowance, Interest Income, Accrual Method	5	59
With related allowance, Interest Income, Accrual Method	1	1
Residential mortgages
Unpaid Principal Balance [Abstract]
With no related allowance, Unpaid Principal Balance	447		450
Recorded Investment [Abstract]
With no related allowance, Recorded Investment	425		427
Average Recorded Investment [Abstract]
With no related allowance, Average Recorded Investment	426	393
Interest Income, Accrual Method [Abstract]
With no related allowance, Interest Income, Accrual Method	2	2
Consumer loans: | Home equity lines and loans
Unpaid Principal Balance [Abstract]
With no related allowance, Unpaid Principal Balance	61		64
Recorded Investment [Abstract]
With no related allowance, Recorded Investment	61		64
Average Recorded Investment [Abstract]
With no related allowance, Average Recorded Investment	63	84
With related allowance, Average Recorded Investment	0	360
Interest Income, Accrual Method [Abstract]
With no related allowance, Interest Income, Accrual Method	1	1
With related allowance, Interest Income, Accrual Method	0	0
Commercial and industrial | Commercial and agricultural:
Unpaid Principal Balance [Abstract]
With no related allowance, Unpaid Principal Balance	770		861
With related allowance, Unpaid Principal Balance	5,019		5,231
Recorded Investment [Abstract]
With no related allowance, Recorded Investment	773		867
With related allowance, Recorded Investment	5,022		5,266
Allowance for loan losses allocated	4,910		$ 5,135
Average Recorded Investment [Abstract]
With no related allowance, Average Recorded Investment	820	671
With related allowance, Average Recorded Investment	5,144	0
Interest Income, Accrual Method [Abstract]
With no related allowance, Interest Income, Accrual Method	9	9
With related allowance, Interest Income, Accrual Method	$ 0	$ 0