ALLOWANCE FOR LOAN LOSSES - Segregated by loan class (Details) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Loan losses segregated by loan class
Beginning balance	$ 24,778,000	$ 25,006,000	$ 25,006,000
Provision (recapture) for loan loss	413,000	(1,388,000)	(338,000)
Charge-offs	(1,152,000)	(874,000)	(1,125,000)
Recoveries	447,000	1,013,000	1,235,000
Net (charge-offs) recoveries	(705,000)	139,000	110,000
Ending balance	24,486,000	23,757,000	24,778,000
Specific reserve
Loan losses segregated by loan class
Beginning balance	1,035,000
Ending balance	785,000	556,000	1,035,000
General reserve
Loan losses segregated by loan class
Beginning balance	23,743,000
Ending balance	23,701,000	23,201,000	23,743,000
Commercial and industrial
Loan losses segregated by loan class
Beginning balance	7,257,000	6,409,000	6,409,000
Provision (recapture) for loan loss	2,218,000	631,000	642,000
Charge-offs	(1,136,000)	(791,000)	(904,000)
Recoveries	424,000	945,000	1,110,000
Net (charge-offs) recoveries	(712,000)	154,000	206,000
Ending balance	8,763,000	7,194,000	7,257,000
Commercial and industrial | Specific reserve
Loan losses segregated by loan class
Beginning balance	852,000
Ending balance	542,000	424,000	852,000
Commercial and industrial | General reserve
Loan losses segregated by loan class
Beginning balance	6,405,000
Ending balance	8,221,000	6,770,000	6,405,000
Commercial real estate
Loan losses segregated by loan class
Beginning balance	10,375,000	10,770,000	10,770,000
Provision (recapture) for loan loss	(3,467,000)	(1,137,000)	(284,000)
Charge-offs	(9,000)		(120,000)
Recoveries	14,000	7,000	9,000
Net (charge-offs) recoveries	5,000	7,000	(111,000)
Ending balance	6,913,000	9,640,000	10,375,000
Commercial real estate | Specific reserve
Loan losses segregated by loan class
Beginning balance	64,000
Ending balance	1,000		64,000
Commercial real estate | General reserve
Loan losses segregated by loan class
Beginning balance	10,311,000
Ending balance	6,912,000	9,640,000	10,311,000
Construction and development
Loan losses segregated by loan class
Beginning balance	3,482,000	4,598,000	4,598,000
Provision (recapture) for loan loss	124,000	(1,234,000)	(1,116,000)
Ending balance	3,606,000	3,364,000	3,482,000
Construction and development | General reserve
Loan losses segregated by loan class
Beginning balance	3,482,000
Ending balance	3,606,000	3,364,000	3,482,000
1-4 family residential
Loan losses segregated by loan class
Beginning balance	1,326,000	1,286,000	1,286,000
Provision (recapture) for loan loss	1,126,000	(16,000)	35,000
Charge-offs	(3,000)		(8,000)
Recoveries	5,000	12,000	13,000
Net (charge-offs) recoveries	2,000	12,000	5,000
Ending balance	2,454,000	1,282,000	1,326,000
1-4 family residential | Specific reserve
Loan losses segregated by loan class
Beginning balance	119,000
Ending balance	115,000	132,000	119,000
1-4 family residential | General reserve
Loan losses segregated by loan class
Beginning balance	1,207,000
Ending balance	2,339,000	1,150,000	1,207,000
Multi‑family residential
Loan losses segregated by loan class
Beginning balance	1,419,000	916,000	916,000
Provision (recapture) for loan loss	211,000	444,000	503,000
Ending balance	1,630,000	1,360,000	1,419,000
Multi‑family residential | General reserve
Loan losses segregated by loan class
Beginning balance	1,419,000
Ending balance	1,630,000	1,360,000	1,419,000
Consumer
Loan losses segregated by loan class
Beginning balance	566,000	353,000	353,000
Provision (recapture) for loan loss	(173,000)	332,000	263,000
Charge-offs	(1,000)	(83,000)	(93,000)
Recoveries	2,000	24,000	43,000
Net (charge-offs) recoveries	1,000	(59,000)	(50,000)
Ending balance	394,000	626,000	566,000
Consumer | General reserve
Loan losses segregated by loan class
Beginning balance	566,000
Ending balance	394,000	626,000	566,000
Agriculture
Loan losses segregated by loan class
Beginning balance	68,000	79,000	79,000
Provision (recapture) for loan loss	3,000	(27,000)	(63,000)
Recoveries		17,000	52,000
Net (charge-offs) recoveries		17,000	52,000
Ending balance	71,000	69,000	68,000
Agriculture | General reserve
Loan losses segregated by loan class
Beginning balance	68,000
Ending balance	71,000	69,000	68,000
Other
Loan losses segregated by loan class
Beginning balance	285,000	595,000	595,000
Provision (recapture) for loan loss	371,000	(381,000)	(318,000)
Charge-offs	(3,000)
Recoveries	2,000	8,000	8,000
Net (charge-offs) recoveries	(1,000)	8,000	8,000
Ending balance	655,000	222,000	285,000
Other | Specific reserve
Loan losses segregated by loan class
Ending balance	127,000
Other | General reserve
Loan losses segregated by loan class
Beginning balance	285,000
Ending balance	528,000	$ 222,000	285,000
Unfunded Loan Commitment
Loan losses segregated by loan class
Beginning balance	378,000
Ending balance	$ 378,000		$ 378,000