SHORT-TERM BORROWINGS - Schedule of Short-term borrowings (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
SHORT-TERM BORROWINGS
Balance at year end	$ 100,748,000	$ 13,241,000
Line of Credit
SHORT-TERM BORROWINGS
Additional lines of credit available from correspondent banks other than the FHLB	52,000,000
Repurchase Agreements
SHORT-TERM BORROWINGS
Balance at year end	7,878,000	13,241,000	$ 18,334,000
Maximum amount outstanding at any month end	13,782,000	17,827,000	18,614,000
Average balance outstanding during the year	$ 10,425,000	$ 15,394,000	$ 15,834,000
Weighted-average interest rate: At year end (as a percent)	0.13%	0.16%	0.21%
Weighted-average interest rate: Paid during the year (as a percent)	0.14%	0.18%	0.21%
Overnight
SHORT-TERM BORROWINGS
Balance at year end	$ 92,870,000	$ 0	$ 28,304,000
Maximum amount outstanding at any month end	92,870,000	24,000	42,760,000
Average balance outstanding during the year	$ 15,559,000	$ 3,000	$ 23,075,000
Weighted-average interest rate: At year end (as a percent)	1.54%	0.00%	0.43%
Weighted-average interest rate: Paid during the year (as a percent)	1.41%	0.57%	0.36%