LOANS AND ALLOWANCE FOR LOAN LOSSES - Allowances (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Sep. 30, 2019	Dec. 31, 2018
Allowance for loan losses, by portfolio segment [Roll Forward]
Beginning balance	$ 19,656	$ 19,645	$ 18,944	$ 21,161	$ 21,161
Charge-offs	(302)	(440)	(1,155)	(5,315)
Recoveries	128	130	450	418
Net recoveries (charge-offs)	(174)	(310)	(705)	(4,897)
Provision	4,441	300	5,684	3,371
Ending balance	23,923	19,635	23,923	19,635	18,944
Ending allowance balance attributable to loans [Abstract]
Individually evaluated for impairment						$ 8,660	$ 2,189
Collectively evaluated for impairment						15,263	16,755
Total ending allowance balance	19,656	19,645	18,944	21,161	21,161	23,923	18,944
Loans [Abstract]
Loans individually evaluated for impairment						20,617	8,731
Loans collectively evaluated for impairment						1,289,703	1,306,878
Total recorded investment in loans						1,310,320	1,315,609
Commercial and Agricultural
Allowance for loan losses, by portfolio segment [Roll Forward]
Beginning balance	5,476	4,969	5,383	6,976	6,976
Charge-offs	0		(55)	(3,644)
Recoveries	29	13	44	34
Net recoveries (charge-offs)	29	13	(11)	(3,610)
Provision	4,651	285	4,784	1,901
Ending balance	10,156	5,267	10,156	5,267	5,383
Ending allowance balance attributable to loans [Abstract]
Individually evaluated for impairment						6,141	1,743
Collectively evaluated for impairment						4,015	3,640
Total ending allowance balance	5,476	4,969	5,383	6,976	6,976	10,156	5,383
Loans [Abstract]
Loans individually evaluated for impairment						6,349	2,128
Loans collectively evaluated for impairment						221,376	201,284
Total recorded investment in loans						227,725	203,412
Commercial Mortgages
Allowance for loan losses, by portfolio segment [Roll Forward]
Beginning balance	9,545	8,740	8,184	8,514	8,514
Charge-offs	0	0	0	(145)
Recoveries	0	0	2	2
Net recoveries (charge-offs)	0	0	2	(143)
Provision	(285)	(91)	1,074	278
Ending balance	9,260	8,649	9,260	8,649	8,184
Ending allowance balance attributable to loans [Abstract]
Individually evaluated for impairment						2,519	446
Collectively evaluated for impairment						6,741	7,738
Total ending allowance balance	9,545	8,740	8,184	8,514	8,514	9,260	8,184
Loans [Abstract]
Loans individually evaluated for impairment						13,708	6,146
Loans collectively evaluated for impairment						639,697	656,842
Total recorded investment in loans						653,405	662,988
Residential mortgages
Allowance for loan losses, by portfolio segment [Roll Forward]
Beginning balance	1,229	1,445	1,226	1,316	1,316
Charge-offs	(19)	(60)	(60)	(225)
Recoveries	0	0	45	5
Net recoveries (charge-offs)	(19)	(60)	(15)	(220)
Provision	(26)	11	(27)	300
Ending balance	1,184	1,396	1,184	1,396	1,226
Ending allowance balance attributable to loans [Abstract]
Individually evaluated for impairment						0	0
Collectively evaluated for impairment						1,184	1,226
Total ending allowance balance	1,229	1,445	1,226	1,316	1,316	1,184	1,226
Loans [Abstract]
Loans individually evaluated for impairment						407	402
Loans collectively evaluated for impairment						184,162	182,823
Total recorded investment in loans						184,569	183,225
Consumer Loans
Allowance for loan losses, by portfolio segment [Roll Forward]
Beginning balance	3,406	4,491	4,151	4,355	4,355
Charge-offs	(283)	(380)	(1,040)	(1,301)
Recoveries	99	117	359	377
Net recoveries (charge-offs)	(184)	(263)	(681)	(924)
Provision	101	95	(147)	892
Ending balance	3,323	4,323	3,323	4,323	4,151
Ending allowance balance attributable to loans [Abstract]
Individually evaluated for impairment						0	0
Collectively evaluated for impairment						3,323	4,151
Total ending allowance balance	$ 3,406	$ 4,491	$ 4,151	$ 4,355	$ 4,355	3,323	4,151
Loans [Abstract]
Loans individually evaluated for impairment						153	55
Loans collectively evaluated for impairment						244,468	265,929
Total recorded investment in loans						$ 244,621	$ 265,984