ALLOWANCE FOR LOAN LOSSES - Segregated by loan class (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loan losses segregated by loan class
Beginning balance	$ 25,006,000	$ 25,315,000	$ 24,952,000
Provision (recapture) for loan loss	(338,000)	4,575,000	6,950,000
Charge-offs	(1,125,000)	(6,079,000)	(7,602,000)
Recoveries	1,235,000	1,195,000	1,015,000
Net (charge-offs) recoveries	110,000	(4,884,000)	(6,587,000)
Ending balance	24,778,000	25,006,000	25,315,000
Specific reserve
Loan losses segregated by loan class
Beginning balance	668,000	389,000
Ending balance	1,035,000	668,000	389,000
General reserve
Loan losses segregated by loan class
Beginning balance	24,338,000	24,926,000
Ending balance	23,743,000	24,338,000	24,926,000
Commercial and industrial
Loan losses segregated by loan class
Beginning balance	6,409,000	4,746,000	7,160,000
Provision (recapture) for loan loss	642,000	5,537,000	4,272,000
Charge-offs	(904,000)	(4,884,000)	(7,210,000)
Recoveries	1,110,000	1,010,000	524,000
Net (charge-offs) recoveries	206,000	(3,874,000)	(6,686,000)
Ending balance	7,257,000	6,409,000	4,746,000
Commercial and industrial | Specific reserve
Loan losses segregated by loan class
Beginning balance	462,000	357,000
Ending balance	852,000	462,000	357,000
Commercial and industrial | General reserve
Loan losses segregated by loan class
Beginning balance	5,947,000	4,389,000
Ending balance	6,405,000	5,947,000	4,389,000
Commercial real estate
Loan losses segregated by loan class
Beginning balance	10,770,000	7,058,000	6,985,000
Provision (recapture) for loan loss	(284,000)	4,193,000	(189,000)
Charge-offs	(120,000)	(589,000)	(27,000)
Recoveries	9,000	108,000	289,000
Net (charge-offs) recoveries	(111,000)	(481,000)	262,000
Ending balance	10,375,000	10,770,000	7,058,000
Commercial real estate | Specific reserve
Loan losses segregated by loan class
Beginning balance	206,000
Ending balance	64,000	206,000
Commercial real estate | General reserve
Loan losses segregated by loan class
Beginning balance	10,564,000	7,058,000
Ending balance	10,311,000	10,564,000	7,058,000
Construction and development
Loan losses segregated by loan class
Beginning balance	4,598,000	4,504,000	2,991,000
Provision (recapture) for loan loss	(1,116,000)	94,000	1,513,000
Ending balance	3,482,000	4,598,000	4,504,000
Construction and development | Specific reserve
Loan losses segregated by loan class
Beginning balance		26,000
Ending balance			26,000
Construction and development | General reserve
Loan losses segregated by loan class
Beginning balance	4,598,000	4,478,000
Ending balance	3,482,000	4,598,000	4,478,000
One to four family residential
Loan losses segregated by loan class
Beginning balance	1,286,000	2,295,000	1,843,000
Provision (recapture) for loan loss	35,000	(1,012,000)	573,000
Charge-offs	(8,000)	(3,000)	(263,000)
Recoveries	13,000	6,000	142,000
Net (charge-offs) recoveries	5,000	3,000	(121,000)
Ending balance	1,326,000	1,286,000	2,295,000
One to four family residential | Specific reserve
Loan losses segregated by loan class
Ending balance	119,000
One to four family residential | General reserve
Loan losses segregated by loan class
Beginning balance	1,286,000	2,295,000
Ending balance	1,207,000	1,286,000	2,295,000
Multi‑family residential
Loan losses segregated by loan class
Beginning balance	916,000	762,000	500,000
Provision (recapture) for loan loss	503,000	154,000	262,000
Ending balance	1,419,000	916,000	762,000
Multi‑family residential | General reserve
Loan losses segregated by loan class
Beginning balance	916,000	762,000
Ending balance	1,419,000	916,000	762,000
Consumer
Loan losses segregated by loan class
Beginning balance	353,000	363,000	423,000
Provision (recapture) for loan loss	263,000	222,000	(18,000)
Charge-offs	(93,000)	(277,000)	(102,000)
Recoveries	43,000	45,000	60,000
Net (charge-offs) recoveries	(50,000)	(232,000)	(42,000)
Ending balance	566,000	353,000	363,000
Consumer | Specific reserve
Loan losses segregated by loan class
Beginning balance		6,000
Ending balance			6,000
Consumer | General reserve
Loan losses segregated by loan class
Beginning balance	353,000	357,000
Ending balance	566,000	353,000	357,000
Agriculture
Loan losses segregated by loan class
Beginning balance	79,000	93,000	118,000
Provision (recapture) for loan loss	(63,000)	227,000	(25,000)
Charge-offs		(267,000)
Recoveries	52,000	26,000
Net (charge-offs) recoveries	52,000	(241,000)
Ending balance	68,000	79,000	93,000
Agriculture | General reserve
Loan losses segregated by loan class
Beginning balance	79,000	93,000
Ending balance	68,000	79,000	93,000
Other
Loan losses segregated by loan class
Beginning balance	595,000	5,494,000	4,932,000
Provision (recapture) for loan loss	(318,000)	(4,840,000)	562,000
Charge-offs		(59,000)
Recoveries	8,000
Net (charge-offs) recoveries	8,000	(59,000)
Ending balance	285,000	595,000	5,494,000
Other | General reserve
Loan losses segregated by loan class
Beginning balance	595,000	5,494,000
Ending balance	285,000	595,000	$ 5,494,000
Unfunded Loan Commitment
Loan losses segregated by loan class
Beginning balance	366,000
Ending balance	$ 378,000	$ 366,000