LOANS - Summary of Past Due Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 2,485,613	$ 1,129,064
Business Activities Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	15,498	8,928
Current	1,437,132	1,120,136
Total loans	1,452,630	1,129,064
Past Due 90 days and Accruing	494	0
Business Activities Loans | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,840	5,074
Business Activities Loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,882	1,029
Business Activities Loans | 90 Days or Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7,776	2,825
Business Activities Loans | Commercial Real Estate:
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,326	2,414
Current	525,685	415,705
Total loans	534,011	418,119
Past Due 90 days and Accruing	119	0
Business Activities Loans | Commercial Real Estate: | Construction and land development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	637	0
Current	28,255	14,695
Total loans	28,892	14,695
Past Due 90 days and Accruing	0	0
Business Activities Loans | Commercial Real Estate: | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7,689	2,414
Current	497,430	401,010
Total loans	505,119	403,424
Past Due 90 days and Accruing	119	0
Business Activities Loans | Commercial Real Estate: | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	965	195
Business Activities Loans | Commercial Real Estate: | 30-59 Days Past Due | Construction and land development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Business Activities Loans | Commercial Real Estate: | 30-59 Days Past Due | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	965	195
Business Activities Loans | Commercial Real Estate: | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,659	554
Business Activities Loans | Commercial Real Estate: | 60-89 Days Past Due | Construction and land development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Business Activities Loans | Commercial Real Estate: | 60-89 Days Past Due | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,659	554
Business Activities Loans | Commercial Real Estate: | 90 Days or Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,702	1,665
Business Activities Loans | Commercial Real Estate: | 90 Days or Greater Past Due | Construction and land development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	637	0
Business Activities Loans | Commercial Real Estate: | 90 Days or Greater Past Due | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,065	1,665
Business Activities Loans | Commercial and Industrial:
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,616	538
Current	266,388	150,702
Total loans	268,004	151,240
Past Due 90 days and Accruing	176	0
Business Activities Loans | Commercial and Industrial: | Other Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,217	307
Current	196,834	103,279
Total loans	198,051	103,586
Past Due 90 days and Accruing	21	0
Business Activities Loans | Commercial and Industrial: | Agricultural and other loans to farmers
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	399	231
Current	27,189	31,577
Total loans	27,588	31,808
Past Due 90 days and Accruing	155	0
Business Activities Loans | Commercial and Industrial: | Tax exempt
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Current	42,365	15,846
Total loans	42,365	15,846
Past Due 90 days and Accruing	0	0
Business Activities Loans | Commercial and Industrial: | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	228	292
Business Activities Loans | Commercial and Industrial: | 30-59 Days Past Due | Other Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	186	61
Business Activities Loans | Commercial and Industrial: | 30-59 Days Past Due | Agricultural and other loans to farmers
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	42	231
Business Activities Loans | Commercial and Industrial: | 30-59 Days Past Due | Tax exempt
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Business Activities Loans | Commercial and Industrial: | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	488	45
Business Activities Loans | Commercial and Industrial: | 60-89 Days Past Due | Other Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	329	45
Business Activities Loans | Commercial and Industrial: | 60-89 Days Past Due | Agricultural and other loans to farmers
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	159	0
Business Activities Loans | Commercial and Industrial: | 60-89 Days Past Due | Tax exempt
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Business Activities Loans | Commercial and Industrial: | 90 Days or Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	900	201
Business Activities Loans | Commercial and Industrial: | 90 Days or Greater Past Due | Other Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	702	201
Business Activities Loans | Commercial and Industrial: | 90 Days or Greater Past Due | Agricultural and other loans to farmers
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	198	0
Business Activities Loans | Commercial and Industrial: | 90 Days or Greater Past Due | Tax exempt
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Business Activities Loans | Total Commercial Loans:
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	9,942	2,952
Current	792,073	566,407
Total loans	802,015	569,359
Past Due 90 days and Accruing	295	0
Business Activities Loans | Total Commercial Loans: | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,193	487
Business Activities Loans | Total Commercial Loans: | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,147	599
Business Activities Loans | Total Commercial Loans: | 90 Days or Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,602	1,866
Business Activities Loans | Residential Real Estate:
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,782	5,851
Current	586,629	500,761
Total loans	591,411	506,612
Past Due 90 days and Accruing	0	0
Business Activities Loans | Residential Real Estate: | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,782	5,851
Current	586,629	500,761
Total loans	591,411	506,612
Past Due 90 days and Accruing	0	0
Business Activities Loans | Residential Real Estate: | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,096	4,484
Business Activities Loans | Residential Real Estate: | 30-59 Days Past Due | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,096	4,484
Business Activities Loans | Residential Real Estate: | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	711	429
Business Activities Loans | Residential Real Estate: | 60-89 Days Past Due | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	711	429
Business Activities Loans | Residential Real Estate: | 90 Days or Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	975	938
Business Activities Loans | Residential Real Estate: | 90 Days or Greater Past Due | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	975	938
Business Activities Loans | Consumer:
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	774	125
Current	58,430	52,968
Total loans	59,204	53,093
Past Due 90 days and Accruing	199	0
Business Activities Loans | Consumer: | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	714	15
Current	50,662	46,906
Total loans	51,376	46,921
Past Due 90 days and Accruing	199	0
Business Activities Loans | Consumer: | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	60	110
Current	7,768	6,062
Total loans	7,828	6,172
Past Due 90 days and Accruing	0	0
Business Activities Loans | Consumer: | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	551	103
Business Activities Loans | Consumer: | 30-59 Days Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	515	0
Business Activities Loans | Consumer: | 30-59 Days Past Due | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	36	103
Business Activities Loans | Consumer: | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	24	1
Business Activities Loans | Consumer: | 60-89 Days Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Business Activities Loans | Consumer: | 60-89 Days Past Due | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	24	1
Business Activities Loans | Consumer: | 90 Days or Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	199	21
Business Activities Loans | Consumer: | 90 Days or Greater Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	199	15
Business Activities Loans | Consumer: | 90 Days or Greater Past Due | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	6
Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,088
Acquired Credit Impaired	12,587
Total loans	1,032,983
Past Due 90 days and Accruing	16
Acquired Loans | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,406
Acquired Loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	528
Acquired Loans | 90 Days or Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,154
Acquired Loans | Commercial Real Estate:
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	822
Acquired Credit Impaired	8,655
Total loans	292,735	0
Past Due 90 days and Accruing	0
Acquired Loans | Commercial Real Estate: | Construction and land development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	133
Acquired Credit Impaired	258
Total loans	16,781	0
Past Due 90 days and Accruing	0
Acquired Loans | Commercial Real Estate: | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	689
Acquired Credit Impaired	8,397
Total loans	275,954	0
Past Due 90 days and Accruing	0
Acquired Loans | Commercial Real Estate: | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	402
Acquired Loans | Commercial Real Estate: | 30-59 Days Past Due | Construction and land development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	124
Acquired Loans | Commercial Real Estate: | 30-59 Days Past Due | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	278
Acquired Loans | Commercial Real Estate: | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	9
Acquired Loans | Commercial Real Estate: | 60-89 Days Past Due | Construction and land development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	9
Acquired Loans | Commercial Real Estate: | 60-89 Days Past Due | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0
Acquired Loans | Commercial Real Estate: | 90 Days or Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	411
Acquired Loans | Commercial Real Estate: | 90 Days or Greater Past Due | Construction and land development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0
Acquired Loans | Commercial Real Estate: | 90 Days or Greater Past Due | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	411
Acquired Loans | Commercial and Industrial:
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	188
Acquired Credit Impaired	632
Total loans	111,419	0
Past Due 90 days and Accruing	0
Acquired Loans | Commercial and Industrial: | Other Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	188
Acquired Credit Impaired	632
Total loans	68,069	0
Past Due 90 days and Accruing	0
Acquired Loans | Commercial and Industrial: | Agricultural and other loans to farmers
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0
Acquired Credit Impaired	0
Total loans	0	0
Past Due 90 days and Accruing	0
Acquired Loans | Commercial and Industrial: | Tax exempt
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0
Acquired Credit Impaired	0
Total loans	43,350	$ 0
Past Due 90 days and Accruing	0
Acquired Loans | Commercial and Industrial: | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	125
Acquired Loans | Commercial and Industrial: | 30-59 Days Past Due | Other Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	125
Acquired Loans | Commercial and Industrial: | 30-59 Days Past Due | Agricultural and other loans to farmers
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0
Acquired Loans | Commercial and Industrial: | 30-59 Days Past Due | Tax exempt
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0
Acquired Loans | Commercial and Industrial: | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	14
Acquired Loans | Commercial and Industrial: | 60-89 Days Past Due | Other Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	14
Acquired Loans | Commercial and Industrial: | 60-89 Days Past Due | Agricultural and other loans to farmers
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0
Acquired Loans | Commercial and Industrial: | 60-89 Days Past Due | Tax exempt
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0
Acquired Loans | Commercial and Industrial: | 90 Days or Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	49
Acquired Loans | Commercial and Industrial: | 90 Days or Greater Past Due | Other Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	49
Acquired Loans | Commercial and Industrial: | 90 Days or Greater Past Due | Agricultural and other loans to farmers
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0
Acquired Loans | Commercial and Industrial: | 90 Days or Greater Past Due | Tax exempt
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0
Acquired Loans | Total Commercial Loans:
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,010
Acquired Credit Impaired	9,287
Total loans	404,154
Past Due 90 days and Accruing	0
Acquired Loans | Total Commercial Loans: | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	527
Acquired Loans | Total Commercial Loans: | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	23
Acquired Loans | Total Commercial Loans: | 90 Days or Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	460
Acquired Loans | Residential Real Estate:
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,754
Acquired Credit Impaired	3,259
Total loans	564,271
Past Due 90 days and Accruing	0
Acquired Loans | Residential Real Estate: | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,754
Acquired Credit Impaired	3,259
Total loans	564,271
Past Due 90 days and Accruing	0
Acquired Loans | Residential Real Estate: | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	752
Acquired Loans | Residential Real Estate: | 30-59 Days Past Due | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	752
Acquired Loans | Residential Real Estate: | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	388
Acquired Loans | Residential Real Estate: | 60-89 Days Past Due | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	388
Acquired Loans | Residential Real Estate: | 90 Days or Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	614
Acquired Loans | Residential Real Estate: | 90 Days or Greater Past Due | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	614
Acquired Loans | Consumer:
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	324
Acquired Credit Impaired	41
Total loans	64,558
Past Due 90 days and Accruing	16
Acquired Loans | Consumer: | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	322
Acquired Credit Impaired	38
Total loans	62,217
Past Due 90 days and Accruing	16
Acquired Loans | Consumer: | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2
Acquired Credit Impaired	3
Total loans	2,341
Past Due 90 days and Accruing	0
Acquired Loans | Consumer: | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	127
Acquired Loans | Consumer: | 30-59 Days Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	125
Acquired Loans | Consumer: | 30-59 Days Past Due | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2
Acquired Loans | Consumer: | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	117
Acquired Loans | Consumer: | 60-89 Days Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	117
Acquired Loans | Consumer: | 60-89 Days Past Due | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0
Acquired Loans | Consumer: | 90 Days or Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	80
Acquired Loans | Consumer: | 90 Days or Greater Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	80
Acquired Loans | Consumer: | 90 Days or Greater Past Due | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 0