INCOME TAXES - Schedule of Effective Income Tax Rate (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount:
Provision at expected rate									$ 5,859,000	$ 5,804,000	$ 5,996,000
(Decrease) increase in tax resulting from
Tax-exempt income									(811,000)	(1,092,000)	(1,492,000)
Tax credits									(177,000)	(312,000)	(737,000)
Change in corporate tax rate									2,724,000	0.0000	0
Other, net									(136,000)	197,000	(31,000)
Total provision	$ 3,968,000	$ 1,282,000	$ 1,223,000	$ 986,000	$ 1,290,000	$ 1,273,000	$ 1,152,000	$ 882,000	$ 7,459,000	$ 4,597,000	$ 3,736,000
Effective Income Tax Rate Reconciliation, Percent:
Provision at expected rate (as a percent)									34.00%	34.00%	34.00%
(Decrease) increase in tax resulting from:
Tax-exempt income (as a percent)									(4.71%)	(6.40%)	(8.46%)
Tax credits (as a percent)									(1.03%)	(1.83%)	(4.17%)
Change in corporate tax rate (as a percent)									15.81%	0.00%	0.00%
Other, net (as a percent)									(0.78%)	1.16%	(0.18%)
Effective income tax provision (benefit) and rate (as a percent)									43.29%	26.93%	21.19%