LOANS, ALLOWANCE FOR LOAN LOSSES, AND CREDIT QUALITY - Summary of loans by credit quality indicator based on internally assigned credit grade (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 2,573,751	$ 2,166,181
Percent of total	100.00%	100.00%
Grades 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 2,457,922	$ 2,061,424
Percent of total	95.50%	95.10%
Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 63,966	$ 58,822
Percent of total	2.50%	2.70%
Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 15,152	$ 18,607
Percent of total	0.60%	0.90%
Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 36,711	$ 27,328
Percent of total	1.40%	1.30%
Retail & other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 30,211	$ 26,493
Retail & other | Grades 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	30,210	26,493
Retail & other | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Retail & other | Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Retail & other | Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	1	0
Commercial Portfolio Segment | Commercial & industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	806,189	684,920
Commercial Portfolio Segment | Commercial & industrial | Grades 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	765,073	649,475
Commercial Portfolio Segment | Commercial & industrial | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	20,199	16,145
Commercial Portfolio Segment | Commercial & industrial | Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	7,663	6,178
Commercial Portfolio Segment | Commercial & industrial | Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	13,254	13,122
Commercial Portfolio Segment | Owner-occupied CRE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	496,372	441,353
Commercial Portfolio Segment | Owner-occupied CRE | Grades 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	464,661	405,198
Commercial Portfolio Segment | Owner-occupied CRE | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	20,855	22,776
Commercial Portfolio Segment | Owner-occupied CRE | Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	953	6,569
Commercial Portfolio Segment | Owner-occupied CRE | Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	9,903	6,810
Commercial Portfolio Segment | Agricultural (“AG”) production
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	35,982	35,625
Commercial Portfolio Segment | Agricultural (“AG”) production | Grades 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	27,521	29,363
Commercial Portfolio Segment | Agricultural (“AG”) production | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	3,174	3,302
Commercial Portfolio Segment | Agricultural (“AG”) production | Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	1,229	2,351
Commercial Portfolio Segment | Agricultural (“AG”) production | Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	4,058	609
Commercial Real Estate Portfolio Segment | AG real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	59,468	53,444
Commercial Real Estate Portfolio Segment | AG real estate | Grades 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	49,561	46,248
Commercial Real Estate Portfolio Segment | AG real estate | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	3,611	3,246
Commercial Real Estate Portfolio Segment | AG real estate | Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	2,046	2,983
Commercial Real Estate Portfolio Segment | AG real estate | Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	4,250	967
Commercial Real Estate Portfolio Segment | CRE investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	443,218	343,652
Commercial Real Estate Portfolio Segment | CRE investment | Grades 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	430,794	334,080
Commercial Real Estate Portfolio Segment | CRE investment | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	8,085	6,792
Commercial Real Estate Portfolio Segment | CRE investment | Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	2,578	0
Commercial Real Estate Portfolio Segment | CRE investment | Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	1,761	2,780
Commercial Real Estate Portfolio Segment | Construction & land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	92,970	80,599
Commercial Real Estate Portfolio Segment | Construction & land development | Grades 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	90,523	75,365
Commercial Real Estate Portfolio Segment | Construction & land development | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	2,213	5,138
Commercial Real Estate Portfolio Segment | Construction & land development | Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	15	16
Commercial Real Estate Portfolio Segment | Construction & land development | Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	219	80
Residential | Residential first mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	432,167	357,841
Residential | Residential first mortgage | Grades 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	424,044	353,239
Residential | Residential first mortgage | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	4,677	1,406
Residential | Residential first mortgage | Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	668	510
Residential | Residential first mortgage | Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	2,778	2,686
Residential | Residential junior mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	122,771	111,328
Residential | Residential junior mortgage | Grades 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	122,249	111,037
Residential | Residential junior mortgage | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	35	17
Residential | Residential junior mortgage | Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Residential | Residential junior mortgage | Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	487	274
Residential | Residential construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	54,403	30,926
Residential | Residential construction | Grades 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	53,286	30,926
Residential | Residential construction | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	1,117	0
Residential | Residential construction | Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Residential | Residential construction | Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 0	$ 0