LOANS - Summary of Total Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	$ 2,485,066	$ 2,485,613
Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	1,533,325	1,452,630
Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	951,741	1,032,983
Total Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	838,546	826,746
Total Commercial Real Estate | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	568,302	534,011
Total Commercial Real Estate | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	270,244	292,735
Total Commercial Real Estate | Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	37,264	45,673
Total Commercial Real Estate | Construction and land development | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	27,722	28,892
Total Commercial Real Estate | Construction and land development | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	9,542	16,781
Total Commercial Real Estate | Other commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	801,282	781,073
Total Commercial Real Estate | Other commercial real estate | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	540,580	505,119
Total Commercial Real Estate | Other commercial real estate | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	260,702	275,954
Total Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	400,293	379,423
Total Commercial and Industrial | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	296,827	268,004
Total Commercial and Industrial | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	103,466	111,419
Total Commercial and Industrial | Other Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	288,396	266,120
Total Commercial and Industrial | Other Commercial | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	226,143	198,051
Total Commercial and Industrial | Other Commercial | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	62,253	68,069
Total Commercial and Industrial | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	25,284	27,588
Total Commercial and Industrial | Agricultural | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	25,284	27,588
Total Commercial and Industrial | Agricultural | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	0	0
Total Commercial and Industrial | Tax exempt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	86,613	85,715
Total Commercial and Industrial | Tax exempt | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	45,400	42,365
Total Commercial and Industrial | Tax exempt | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	41,213	43,350
Total Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	1,238,839	1,206,169
Total Commercial Loans | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	865,129	802,015
Total Commercial Loans | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	373,710	404,154
Total Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	1,127,895	1,155,682
Total Residential Real Estate | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	606,128	591,411
Total Residential Real Estate | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	521,767	564,271
Total Residential Real Estate | Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	1,127,895	1,155,682
Total Residential Real Estate | Residential mortgages | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	606,128	591,411
Total Residential Real Estate | Residential mortgages | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	521,767	564,271
Total Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	118,332	123,762
Total Consumer | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	62,068	59,204
Total Consumer | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	56,264	64,558
Total Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	108,310	113,593
Total Consumer | Home equity | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	53,853	51,376
Total Consumer | Home equity | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	54,457	62,217
Total Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	10,022	10,169
Total Consumer | Other consumer | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	8,215	7,828
Total Consumer | Other consumer | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	$ 1,807	$ 2,341