LOAN PERFORMANCE - Aging analysis of loan past due (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Aging analysis
Total past due	$ 6,241,000		$ 2,874,000
Total current loans	2,672,170,000		2,643,799,000
Total Loans	2,678,411,000		2,646,673,000
Interest income that would have been earned under the original terms of the nonaccrual loans	33,000	$ 48,000
30 to 59 days past due
Aging analysis
Total past due	6,202,000		2,071,000
60 to 89 days past due
Aging analysis
Total past due	7,000		563,000
90 days or greater past due
Aging analysis
Total past due	32,000		240,000
Commercial and industrial
Aging analysis
Total past due	1,556,000		935,000
Total current loans	541,094,000		526,672,000
Total Loans	542,650,000		527,607,000
Commercial and industrial | 30 to 59 days past due
Aging analysis
Total past due	1,549,000		664,000
Commercial and industrial | 60 to 89 days past due
Aging analysis
Total past due	7,000		31,000
Commercial and industrial | 90 days or greater past due
Aging analysis
Total past due			240,000
Commercial real estate
Aging analysis
Total past due	1,532,000		865,000
Total current loans	902,863,000		899,881,000
Total Loans	904,395,000		900,746,000
Commercial real estate | 30 to 59 days past due
Aging analysis
Total past due	1,532,000		865,000
Construction and development
Aging analysis
Total past due	2,973,000		532,000
Total current loans	555,370,000		527,280,000
Total Loans	558,343,000		527,812,000
Construction and development | 30 to 59 days past due
Aging analysis
Total past due	2,973,000
Construction and development | 60 to 89 days past due
Aging analysis
Total past due			532,000
1-4 family residential
Aging analysis
Total past due	165,000		499,000
Total current loans	275,977,000		279,693,000
Total Loans	276,142,000		280,192,000
1-4 family residential | 30 to 59 days past due
Aging analysis
Total past due	133,000		499,000
1-4 family residential | 90 days or greater past due
Aging analysis
Total past due	32,000
Multi‑family residential
Aging analysis
Total current loans	267,152,000		277,209,000
Total Loans	267,152,000		277,209,000
Consumer
Aging analysis
Total past due	15,000		43,000
Total current loans	38,118,000		36,739,000
Total Loans	38,133,000		36,782,000
Consumer | 30 to 59 days past due
Aging analysis
Total past due	15,000		43,000
Agriculture
Aging analysis
Total current loans	7,520,000		9,812,000
Total Loans	7,520,000		9,812,000
Other
Aging analysis
Total current loans	84,076,000		86,513,000
Total Loans	$ 84,076,000		$ 86,513,000