LOAN PERFORMANCE - Aging analysis of past due loans, by loan class (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Aging analysis
Total current loans	$ 2,875,291,000	$ 2,930,758,000
Total gross loans	2,876,427,000	2,936,670,000
Interest income that would have been earned under the original terms of the nonaccrual loans	855,000	804,000	$ 57,000
30 to 59 days past due
Aging analysis
Total current loans	905,000	1,463,000
60 to 89 days past due
Aging analysis
Total current loans	34,000	2,074,000
90 days or greater past due
Aging analysis
Total current loans	197,000	2,375,000
Total Past Due
Aging analysis
Total current loans	1,136,000	5,912,000
Commercial and industrial
Aging analysis
Total current loans	634,370,000	738,582,000
Total gross loans	634,384,000	742,957,000
Commercial and industrial | 30 to 59 days past due
Aging analysis
Total current loans	14,000	51,000
Commercial and industrial | 60 to 89 days past due
Aging analysis
Total current loans		2,055,000
Commercial and industrial | 90 days or greater past due
Aging analysis
Total current loans		2,269,000
Commercial and industrial | Total Past Due
Aging analysis
Total current loans	14,000	4,375,000
Commercial real estate
Aging analysis
Total current loans	1,091,264,000	1,041,998,000
Total gross loans	1,091,969,000	1,041,998,000
Commercial real estate | 30 to 59 days past due
Aging analysis
Total current loans	650,000
Commercial real estate | 90 days or greater past due
Aging analysis
Total current loans	55,000
Commercial real estate | Total Past Due
Aging analysis
Total current loans	705,000
Construction and development
Aging analysis
Total current loans	460,577,000	522,705,000
Total gross loans	460,719,000	522,705,000
Construction and development | 90 days or greater past due
Aging analysis
Total current loans	142,000
Construction and development | Total Past Due
Aging analysis
Total current loans	142,000
1-4 family residential
Aging analysis
Total current loans	277,089,000	238,390,000
Total gross loans	277,273,000	239,872,000
1-4 family residential | 30 to 59 days past due
Aging analysis
Total current loans	150,000	1,357,000
1-4 family residential | 60 to 89 days past due
Aging analysis
Total current loans	34,000	19,000
1-4 family residential | 90 days or greater past due
Aging analysis
Total current loans		106,000
1-4 family residential | Total Past Due
Aging analysis
Total current loans	184,000	1,482,000
Multifamily residential
Aging analysis
Total current loans	286,396,000	258,346,000
Total gross loans	286,396,000	258,346,000
Consumer
Aging analysis
Total current loans	28,040,000	33,879,000
Total gross loans	28,090,000	33,884,000
Consumer | 30 to 59 days past due
Aging analysis
Total current loans	50,000	5,000
Consumer | Total Past Due
Aging analysis
Total current loans	50,000	5,000
Agriculture
Aging analysis
Total current loans	7,941,000	8,620,000
Total gross loans	7,941,000	8,670,000
Agriculture | 30 to 59 days past due
Aging analysis
Total current loans		50,000
Agriculture | Total Past Due
Aging analysis
Total current loans		50,000
Other
Aging analysis
Total current loans	89,614,000	88,238,000
Total gross loans	89,655,000	$ 88,238,000
Other | 30 to 59 days past due
Aging analysis
Total current loans	41,000
Other | Total Past Due
Aging analysis
Total current loans	$ 41,000