LOAN PERFORMANCE - Aging analysis of past due loans, by loan class (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Aging analysis
Total past due	$ 5,912,000	$ 2,874,000
Total current loans	2,930,758,000	2,643,799,000
Total Loans	2,936,670,000	2,646,673,000
Interest income that would have been earned under the original terms of the nonaccrual loans	804,000	57,000	$ 163,000
30 to 59 days past due
Aging analysis
Total past due	1,463,000	2,071,000
60 to 89 days past due
Aging analysis
Total past due	2,074,000	563,000
90 days or greater past due
Aging analysis
Total past due	2,375,000	240,000
Commercial and industrial
Aging analysis
Total past due	4,375,000	935,000
Total current loans	738,582,000	526,672,000
Total Loans	742,957,000	527,607,000
Commercial and industrial | 30 to 59 days past due
Aging analysis
Total past due	51,000	664,000
Commercial and industrial | 60 to 89 days past due
Aging analysis
Total past due	2,055,000	31,000
Commercial and industrial | 90 days or greater past due
Aging analysis
Total past due	2,269,000	240,000
Commercial real estate
Aging analysis
Total past due		865,000
Total current loans	1,041,998,000	899,881,000
Total Loans	1,041,998,000	900,746,000
Commercial real estate | 30 to 59 days past due
Aging analysis
Total past due		865,000
Construction and development
Aging analysis
Total past due		532,000
Total current loans	522,705,000	527,280,000
Total Loans	522,705,000	527,812,000
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	1,482,000	499,000
Total current loans	238,390,000	279,693,000
Total Loans	239,872,000	280,192,000
1-4 family residential | 30 to 59 days past due
Aging analysis
Total past due	1,357,000	499,000
1-4 family residential | 60 to 89 days past due
Aging analysis
Total past due	19,000
1-4 family residential | 90 days or greater past due
Aging analysis
Total past due	106,000
Multifamily residential
Aging analysis
Total current loans	258,346,000	277,209,000
Total Loans	258,346,000	277,209,000
Consumer
Aging analysis
Total past due	5,000	43,000
Total current loans	33,879,000	36,739,000
Total Loans	33,884,000	36,782,000
Consumer | 30 to 59 days past due
Aging analysis
Total past due	5,000	43,000
Agriculture
Aging analysis
Total past due	50,000
Total current loans	8,620,000	9,812,000
Total Loans	8,670,000	9,812,000
Agriculture | 30 to 59 days past due
Aging analysis
Total past due	50,000
Other
Aging analysis
Total current loans	88,238,000	86,513,000
Total Loans	$ 88,238,000	$ 86,513,000