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, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 2,166,181	$ 2,087,925
Percent of total	100.00%	100.00%
Grades 1- 4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 2,061,424	$ 1,979,429
Percent of total	95.10%	94.80%
Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 58,822	$ 58,354
Percent of total	2.70%	2.80%
Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 18,607	$ 23,461
Percent of total	0.90%	1.10%
Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 27,328	$ 26,681
Percent of total	1.30%	1.30%
Grade 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 0	$ 0
Percent of total	0.00%	0.00%
Grade 9
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 0	$ 0
Percent of total	0.00%	0.00%
Retail & other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 26,493	$ 22,815
Retail & other | Grades 1- 4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	26,493	22,811
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	0	4
Retail & other | Grade 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Retail & other | Grade 9
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Commercial Portfolio Segment | Commercial & industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	684,920	637,337
Commercial Portfolio Segment | Commercial & industrial | Grades 1- 4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	649,475	597,854
Commercial Portfolio Segment | Commercial & industrial | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	16,145	12,999
Commercial Portfolio Segment | Commercial & industrial | Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	6,178	16,129
Commercial Portfolio Segment | Commercial & industrial | Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	13,122	10,355
Commercial Portfolio Segment | Commercial & industrial | Grade 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Commercial Portfolio Segment | Commercial & industrial | Grade 9
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Commercial Portfolio Segment | Owner-occupied CRE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	441,353	430,043
Commercial Portfolio Segment | Owner-occupied CRE | Grades 1- 4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	405,198	397,357
Commercial Portfolio Segment | Owner-occupied CRE | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	22,776	23,340
Commercial Portfolio Segment | Owner-occupied CRE | Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	6,569	6,442
Commercial Portfolio Segment | Owner-occupied CRE | Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	6,810	2,904
Commercial Portfolio Segment | Owner-occupied CRE | Grade 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Commercial Portfolio Segment | Owner-occupied CRE | Grade 9
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Commercial Portfolio Segment | Agricultural (“AG”) production
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	35,625	35,455
Commercial Portfolio Segment | Agricultural (“AG”) production | Grades 1- 4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	29,363	30,431
Commercial Portfolio Segment | Agricultural (“AG”) production | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	3,302	4,000
Commercial Portfolio Segment | Agricultural (“AG”) production | Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	2,351	0
Commercial Portfolio Segment | Agricultural (“AG”) production | Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	609	1,024
Commercial Portfolio Segment | Agricultural (“AG”) production | Grade 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Commercial Portfolio Segment | Agricultural (“AG”) production | Grade 9
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Commercial Real Estate Portfolio Segment | AG real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	53,444	51,778
Commercial Real Estate Portfolio Segment | AG real estate | Grades 1- 4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	46,248	44,321
Commercial Real Estate Portfolio Segment | AG real estate | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	3,246	4,873
Commercial Real Estate Portfolio Segment | AG real estate | Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	2,983	0
Commercial Real Estate Portfolio Segment | AG real estate | Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	967	2,584
Commercial Real Estate Portfolio Segment | AG real estate | Grade 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Commercial Real Estate Portfolio Segment | AG real estate | Grade 9
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Commercial Real Estate Portfolio Segment | CRE investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	343,652	314,463
Commercial Real Estate Portfolio Segment | CRE investment | Grades 1- 4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	334,080	299,926
Commercial Real Estate Portfolio Segment | CRE investment | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	6,792	8,399
Commercial Real Estate Portfolio Segment | CRE investment | Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	190
Commercial Real Estate Portfolio Segment | CRE investment | Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	2,780	5,948
Commercial Real Estate Portfolio Segment | CRE investment | Grade 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Commercial Real Estate Portfolio Segment | CRE investment | Grade 9
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Commercial Real Estate Portfolio Segment | Construction & land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	80,599	89,660
Commercial Real Estate Portfolio Segment | Construction & land development | Grades 1- 4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	75,365	86,011
Commercial Real Estate Portfolio Segment | Construction & land development | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	5,138	2,758
Commercial Real Estate Portfolio Segment | Construction & land development | Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	16	17
Commercial Real Estate Portfolio Segment | Construction & land development | Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	80	874
Commercial Real Estate Portfolio Segment | Construction & land development | Grade 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Commercial Real Estate Portfolio Segment | Construction & land development | Grade 9
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Residential | Residential first mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	357,841	363,352
Residential | Residential first mortgage | Grades 1- 4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	353,239	358,067
Residential | Residential first mortgage | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	1,406	1,868
Residential | Residential first mortgage | Grade 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	510	683
Residential | Residential first mortgage | Grade 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	2,686	2,734
Residential | Residential first mortgage | Grade 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Residential | Residential first mortgage | Grade 9
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Residential | Residential junior mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	111,328	106,027
Residential | Residential junior mortgage | Grades 1- 4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	111,037	105,736
Residential | Residential junior mortgage | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	17	117
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	274	174
Residential | Residential junior mortgage | Grade 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Residential | Residential junior mortgage | Grade 9
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Residential | Residential construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	30,926	36,995
Residential | Residential construction | Grades 1- 4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	30,926	36,915
Residential | Residential construction | Grade 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	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	80
Residential | Residential construction | Grade 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	0	0
Residential | Residential construction | Grade 9
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 0	$ 0